IS 15935 (2011): Composite Cylinders for on-board Storage ...impregnated continuous filament wound over a metallic or non-metallic liner. NOTE — Composite cylinders using non-metallic

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IS 15935 (2011): Composite Cylinders for on-board Storageof Compressed Natural Gas(CNG) as a Fuel for AutomotiveVehicle [MED 16: Mechanical Engineering]

© BIS 2011

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

December 2011 Price Group 14

IS 15935 : 2011

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Indian Standard

COMPOSITE CYLINDERS FOR ON-BOARD STORAGEOF COMPRESSED NATURAL GAS (CNG) AS A FUEL

FOR AUTOMOTIVE VEHICLE — SPECIFICATION

ICS 23.020;43.060.40

Gas Cylinders Sectional Committee, MED 16

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Gas CylindersSectional Committee had been approved by the Mechanical Engineering Division Council.

Cylinders for the on-board storage of fuel for natural gas vehicle service are required to be light-weight, at thesame time maintaining or improving on the level of safety currently existing for other pressure vessels.

The purpose of this standard is to specify minimum requirements for serially produced light-weight, compositerefillable gas cylinder intended for the on-board storage for high pressure compressed natural gas as a fuel forautomotive vehicles. This standard covers the metal and non-metal lined composite cylinders of the following types:

a) CNG 2 : Metal lined hoop wrapped composite cylindersb) CNG 3 : Metal lined full wrapped composite cylindersc) CNG 4 : Non-metal lined full wrapped composite cylinders

The CNG 1 metal cylinders are covered in IS 15490 : 2004 ‘Cylinders for on-board storage of compressednatural gas as a fuel for automotive vehicles — Specification’.

Considerable assistance has been taken from the following:

a) ISO 11439 : 2000 Gas cylinder — High pressure cylinders for the on-board storage of natural gas asa fuel for automotive vehicles;

b) ISO 11119-1 : 2002 Gas cylinders of composite construction — Specification and test methods —Part 1: Hoop wrapped composite cylinders;

c) ISO 11119-2 : 2002 Gas cylinders of composite construction — Specification and test methods —Part 2: Fully wrapped fiber reinforced composite gas cylinders with load sharingmetal liners;

d) ISO 11623 : 2002 Transportable gas cylinders — Periodic inspection and retesting of compositecylinders;

e) ANSI/CSA NGV2 Basic Requirements for compressed natural gas vehicle (NGV2) fuel containers;f) ISO 7866 : 1999 Gas Cylinders — Refillable seamless aluminum alloy gas cylinders — Design,

construction and testing;g) ISO 14130 : 1997 Fiber reinforced plastic composite — Determination of apparent interlaminar shear

strength by short-beam method;h) NACE-6 Testing of metals for resistance to sulfide stress cracking at ambient temperature;

andj) ISO 7539-6 : 2003 Corrosion of metals and alloys — Stress corrosion testing — Part 6: Preparation and

use of pre-cracked specimens for tests under constant load or constant displacement.

While implementing this standard, the manufacturer and the inspection agency shall ensure compliance withstatutory regulations.

Owners and users of cylinders should note that cylinders designed according to this standard are to operatesafely, if used in accordance with specified service conditions for a specified finite service life only. The expirydate is marked on each cylinder and it is the responsibility of the owner and user to ensure that cylinders areperiodically tested as per norms laid down by statutory authorities.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960‘Rules for rounding off numerical values (revised)’. The number of significant places retained in the rounded offvalue should be the same as that of the specified value in this standard.

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IS 15935 : 2011

Indian Standard

COMPOSITE CYLINDERS FOR ON-BOARD STORAGEOF COMPRESSED NATURAL GAS (CNG) AS A FUEL

FOR AUTOMOTIVE VEHICLE — SPECIFICATION

1 SCOPE

This standard specifies minimum requirements forserially produced light-weight, refillable gas cylinderintended for the on-board storage of high pressurecompressed natural gas as a fuel for automotivevehicles to which the cylinders are to be fixed. Theservice conditions do not cover external loadings whichmay arise from vehicle collisions, etc. This standardcovers metal and non-metal lined composite cylindersof the following types:

a) CNG 2 : Metal lined hoop wrappedcomposite cylinders

b) CNG 3 : Metal lined full wrapped compositecylinders

c) CNG 4 : Non-metal lined full wrappedcomposite cylinders

2 REFERENCES

The following standards contain provisions whichthrough reference in this text, constitute provisions ofthis standard. At the time of publication, the editionsindicated were valid. All standards are subject torevision and parties to agreements based on thisstandard are encouraged to investigate the possibilityof applying the most recent editions of the standardsindicated below:

IS No./ TitleInternational

Standard

1500 : 2005 Method for Brinell hardness test formetallic materials (third revision)

1608 : 2005/ Metallic materials — Tensile testingISO 6892 : 1998 at ambient temperature (third

revision)1757 : 1988 Method for Charpy impact test (V

notch) for metallic material3224 : 2002 Valve fittings for compressed gas

cylinders exceeding liquefiedpetroleum gas (LPG) cylinders —Specification (third revision)

13360 Plastics — Methods of testing: Part 5(Part 5/Sec 1) : Mechanical properties, Section 11996 Determination of tensile properties

— General principles

IS No./ TitleInternational

Standard

13360 Plastics — Methods of testing: Part 5(Part 5/Sec 2) : Mechanical properties, Section 21996 Determination of tensile properties

— Test conditions for moulding andextrusion plastics

13360 Plastics — Methods of testing: Part 6(Part 6/Sec 1) : Thermal properties, Section 1

1999 Determination of vicat softeningtemperature of thermoplasticmaterials

13411 : 1992 Glass reinforced polyester doughmoulding compounds (DMC)

15490 : 2004 Cylinders for on-board storage ofcompressed natural gas as a fuel forautomotive vehicles — Specification

ASTM D3170 : Standard test method for chipping2003 resistance of coating

ASTM D3418 : Standard test method for transition2008 temperatures and enthalpies of fusion

and crystallization of polymers bydifferential scanning calorimetry

3 TERMINOLOGY

For the purpose of this standard, the following termsand definitions shall apply.

3.1 Authorized Inspection Authority — An inspectionagency having qualification and wide experience in thefield of design, manufacture and testing of gas cylindersand recognized by the statutory authority for inspectionand certification of gas cylinders.

3.2 Auto-Frettage — Pressure application procedureused in manufacturing composite cylinders with metalliners, which strains the liner past its yield pointsufficient to cause permanent plastic deformation. Thisresults in the liner having compressive stresses and thefibres having tensile stresses at zero internal pressure.Auto-frettage is a part of the manufacturing operationand is conducted on the metal lined filament woundcylinders prior to hydrostatic pressure testing.

3.3 Auto-Frettage Pressure — Pressure within theover-wrapped cylinder at which the required

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distribution of stresses between the liner and the over-wrap is established.

3.4 Batch (of Composite Cylinders) — Group ofcylinders successively produced from qualified linershaving the same size, design, specified material ofconstruction and process of manufacture. A batch shallbe a group of 200 cylinders plus cylinders fordestructive testing or one shift of successive production,whichever is greater.

3.5 Batch (of Metallic Liners) — Group of linerssuccessively produced having the same nominaldiameter, wall thickness, design, specified material ofconstruction, process of manufacture, equipment formanufacture and heat treatment, and conditions of time,temperature and atmosphere during heat treatment. Abatch shall be a group of 200 liners plus liners fordestructive testing or one shift of successive production,whichever is greater.

3.6 Batch (of Non-metallic Liners) — Group of non-metallic liners successively produced having the samenominal diameter, wall thickness, design, specifiedmaterial of construction, process of manufacture. Abatch shall be a group of 200 liners plus liners fordestructive testing or one shift of successive production,whichever is greater.

3.7 Burst Pressure — The highest pressure reachedin a cylinder during a burst test.

3.8 Composite Cylinder — Cylinder made of resin-impregnated continuous filament wound over a metallicor non-metallic liner.

NOTE — Composite cylinders using non-metallic liners arereferred to as all composite cylinders.

3.9 Controlled Tension Winding — Process used inmanufacturing hoop-wrapped composite cylinders withmetal liners by which compressive stresses in the linerand tensile stresses in the over-wrap at zero internalpressure are obtained by winding the reinforcingfilaments under significant high tension.

3.10 Filling Pressure — Pressure to which a cylinderis filled.

3.11 Finished Cylinders — Completed cylinderswhich are ready for use, typical of normal production,complete with identification marks and externalinsulation specified by the manufacturer, but free fromnon-integral insulation or protection.

3.12 Full Wrapped Cylinder — Cylinder with anoverwrap having a filament wound reinforcement bothin the circumferential and axial direction of the cylinderover the entire liner including the domes.

3.13 Gas Temperature — Temperature of gas in acylinder.

3.14 Hoop Wrapped Cylinder — Cylinder with anoverwrap having a filament wound reinforcement in asubstantially circumferential pattern over thecylindrical portion of the liner so that the filament doesnot carry any significant load in a direction parallel tothe cylinder longitudinal axis.

3.15 Liner — Gas tight inner shell, on whichreinforcing fibres are filament wound to reach thenecessary strength. Two types of liner are described inthis standard; metallic and non-metallic liners. Metallicliners are designed to share the load with thereinforcement and non-metallic liners do not carry anypart of the load.

3.16 Manufacturer — Person or organizationresponsible for the design, fabrication and testing ofthe cylinders.

3.17 Pre-stress or Pre-stressing — The process ofapplying auto-frettage or controlled tension winding.

3.18 Overwrap — Reinforcement system of filamentand resin applied over the liner.

3.19 Service Life — Life, in years, during which thecylinders may safely be used in accordance with thestandard service conditions.

3.20 Settled Pressure — Gas pressure when a givensettled temperature is reached.

3.21 Settled Temperature — Uniform gastemperature after the dissipation of any change intemperature caused by filling.

3.22 Test Pressure — Required pressure appliedduring a pressure test.

3.23 Working Pressure — Settled pressure of 200 barat a uniform temperature of 15°C.

4 SERVICE CONDITIONS

4.1 General

4.1.1 Standard Service Conditions

The standard service conditions in this clause areprovided as the basis for the design, manufacture,inspection, testing and approval of cylinders that areto be mounted permanently on vehicles and used tostore natural gas at ambient temperature for use as afuel on the vehicles.

4.1.2 Use of Cylinders

The service conditions specified are also intended toprovide information on how cylinders aremanufactured in accordance with this standard maysafely be used; this information is intended for:

a) Manufacturers of cylinders;b) Owners of cylinders;

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c) Designers or contractors responsible for theinstallation of cylinders;

d) Designers or owners of equipment used torefuel vehicle cylinders;

e) Suppliers of natural gas; andf) Regulatory authorities who have jurisdiction

over cylinder use.

4.1.3 Service Life

The service life for the cylinders shall be specified bythe manufacturer and shall not exceed 20 years.

For metal lined cylinders, the service life shall be basedupon the rate of fatigue crack growth. The ultrasonicinspection, or equivalent, of each liner shall ensure theabsence of flaws which exceed the maximum allowablesize. This approach permits the optimized design andmanufacture of light weight cylinders for natural gasvehicle service.

For all composite cylinders with non-metallic non-loadbearing liners, the service life shall be demonstratedby appropriate design methods, design qualificationtesting and manufacturing controls.

The requirements for periodic re-qualification byinspection or testing during the service life shall bespecified by the cylinder designer in consultation withstatutory authority on the basis of use under serviceconditions specified herein. The manufacturer shouldclearly specify the user’s obligation to observe therequired cylinder inspection requirements (for examplere-inspection interval by authorized personnel). Thisinformation should be in agreement with the designapproval requirements and should cover the followingaspects:

a) Cylinders involved in collisions — Cylinderswhich have been involved in vehicle collisionshould be re-inspected by an authorizedinspection agency. Cylinders which have notexperienced any impact damage from thecollision may be returned to service, otherwisethe cylinder should be returned to themanufacturer for evaluation.

b) Cylinders involved in fires — Cylinders whichhave been subject to the action of fire should bere-inspected by an authorized inspection agencyor condemned and removed from service.

Periodic inspection of cylinders shall be done as perthe requirements of statutory authority.

4.2 Maximum Pressures

This standard is based upon a working pressure of200 bar settled at 15°C for natural gas as a fuel with amaximum filling pressure of 260 bar. Other workingpressures may be accommodated by adjusting the

pressure by the appropriate factor (ratio), for example,a 250 bar working pressure system will requirepressures to be multiplied by 1.25. Except wherepressures have been adjusted in this way, the cylindershall be designed to be suitable for the followingpressure limits:

a) A pressure that would settle to 200 bar at asettled temperature of 15°C; and

b) The maximum pressure shall not exceed260 bar regardless of filling conditions ortemperature.

4.3 Design Number of Filling Cycles

Cylinders shall be designed to be filled up to a settledpressure of 200 bar at a settled gas temperature of 15°Cfor up to 1 000 times per year of service.

4.4 Temperature Range

4.4.1 Gas Temperature

Cylinder shall be designed to be suitable for thefollowing gas temperature limits:

a) The settled temperature of gas in cylinders,which may vary from a low of –20°C to ahigh of +65°C.

b) The developed gas temperatures during fillingand discharge, which may vary beyond theselimits.

4.4.2 Cylinder Temperature

Cylinder shall be designed to be suitable for thefollowing material temperature limits:

a) Temperature of the cylinder materials mayvary from –20°C to +82°C.

b) Temperatures over +65°C shall be sufficientlylocal, or of short enough duration, that thetemperature of gas in the cylinder neverexceeds +65°C, except under the conditionsof 4.4.1 (b).

4.5 Gas Composition

4.5.1 General

Cylinders shall be designed to tolerate being filled withnatural gas meeting the specification either of dry gasor wet gas as follows. Methanol and/or glycol shallnot be deliberately added to the natural gas.

4.5.2 Dry Gas

Water vapour shall be limited to less than 32 mg/m3

(that is a pressure dew point of –9°C at 200 bar).Constituent maximum limits shall be:

Hydrogen sulphide and other soluble sulphides

: 23 mg/m3

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Oxygen : 1 percent (volume fraction)

Hydrogen, when cylinders are manufactured from a steel with an ultimate tensile strength exceeding 950 MPa

: 2 percent (volume fraction)

4.5.3 Wet Gas

This is gas that has higher water content than that ofdry gas. Constituent maximum limits shall be:

Hydrogen sulphide and other soluble sulphides

: 23 mg/m3

Oxygen : 1 percent (volume fraction) Carbon dioxide : 4 percent (volume fraction) Hydrogen : 0.1 percent (volume fraction)

4.6 External Surfaces

It is not necessary for cylinders to be designed forcontinuous exposure to mechanical or chemical attack,for example leakage from cargo that may be carried onvehicles or severe abrasion damage from road conditions.However, cylinder external surfaces shall be designed towithstand inadvertent exposure to the following,consistent with installation being carried out in accordancewith the instructions to be provided with the cylinder:

a) Water, either by intermittent immersion orroad spray;

b) Salt, due to the operation of the vehicle nearthe ocean or where ice-melting salt used;

c) Ultra-violet radiation from sunlight;d) Impact of gravel;e) Solvents, acids and alkalis, fertilizers;f) Automotive fluids, including petrol, hydraulic

fluids, battery acid, glycol and oils; andg) Exhaust gases.

5 APPROVAL AND CERTIFICATION

5.1 Inspection and Testing

In order to ensure that the cylinders are in compliancewith this standard, they shall be subjected to designapproval in accordance with 5.2, and inspection andtesting in accordance with either 6 or 7 or 8 asappropriate to the construction. This shall be carriedout by an authorized inspection authority. Testprocedures are detailed in Annex A and Annex B.

5.2 Type Approval Procedure

5.2.1 General

Type approval consists of following two parts:

a) The design submission comprising ofinformation furnished by the manufacturer to

the inspector for appraisal/scrutiny and furtherrecommendations to the statutory authorityfor approval, as detailed in 5.2.2.

b) Prototype testing, comprising testing carriedout under the supervision of the inspector. Thecylinder material, design, manufacture andexamination shall be proved to be adequatefor their intended service by meeting therequirements of the prototype tests specifiedin 6.5 or 7.5 or 8.5 as appropriate for theparticular cylinder design.

The test data shall also document the dimension, wallthicknesses and weights of each of the test cylinders.

5.2.2 Design Approval

Cylinder designs shall be approved by the statutoryauthority. The following information shall be submittedby the manufacturer to the inspector for examinationand further approval by statutory authority:

a) Statement of service, in accordance with 5.2.3;b) Design data, in accordance with 5.2.4;c) Manufacturing data, in accordance with 5.2.5;d) Quality system, in accordance with 5.2.6;e) Fracture performance and NDE (non-

destructive examination) defect size, inaccordance with 5.2.7;

f) Specification sheet, in accordance with 5.2.8;and

g) Additional supporting data, in accordancewith 5.2.9.

5.2.3 Statement of Service

The purpose of this statement of service is to guide theuser and the installer of cylinders as well as to informthe inspector. The statement of service shall include:

a) A statement that the cylinder design is suitablefor use in the service conditions defined in 4for the service life of the cylinder;

b) A statement of the service life;c) A specification for minimum in-service

inspection and testing requirements;d) A specification for the pressure relief devices;e) A specification for the support methods,

protective covering and any other itemsrequired but not provided;

f) A description of the cylinder design; andg) Any other information necessary to ensure the

safe use and inspection of the cylinder.

5.2.4 Design Data

5.2.4.1 Drawings

Drawings shall show at least the following:

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a) Title, reference number, date of issue, andrevision numbers with dates of issue, ifapplicable;

b) Reference to this standard and the cylindertype;

c) All dimensions complete with tolerances,including details of end closure shapes withminimum thicknesses and of openings;

d) Mass, complete with tolerance of cylinders;e) Material specifications, complete with

minimum mechanical and chemical propertiesor tolerance ranges and, for metal liners, thespecified hardness range; and

f) Other data such as, auto-frettage pressurerange, minimum test pressure details of thefire protection system and of any exteriorprotective coating.

5.2.4.2 Stress analysis report

A finite element stress analysis or other stress analysisshall be carried out. A table summarizing the calculatedstresses shall be provided.

5.2.4.3 Material property data

A detailed description of the materials and tolerancesof the materials properties used in the design shall beprovided. Test data shall also be presentedcharacterizing the mechanical properties and thesuitability of the materials for service under theconditions specified in 4.

5.2.4.4 Fire protection

The arrangement of pressure relief devices that willprotect the cylinder from sudden rupture when exposedto the fire conditions specified in A-14 shall bespecified. Test data shall substantiate the effectivenessof the specified fire protection system.

5.2.5 Manufacturing Data

Details of all fabrication processes, non-destructiveexaminations, production tests and batch tests shall beprovided. The tolerances for all production processsuch as heat treatment, end forming resin-mix ratio,filament tension and speed for controlled tensionwinding, curing times and temperatures, and auto-frettage procedures, surface finish, thread details,acceptance criteria for ultrasonic scanning (orequivalent) and maximum lot sizes for batch tests shallalso be specified.

5.2.6 Quality Control Programme

The manufacturer shall specify methods andprocedures in accordance with a quality assurancesystem.

5.2.7 Fracture Performance and Non-destructiveExamination (NDE) Defect Size

The manufacturer shall specify the maximum defectsize for non-destructive examination which will ensureleak-before-break (LBB) fracture performance and willprevent failure of the cylinder during its service lifedue to fatigue, or failure of the cylinder by rupture.

The maximum defect size shall be established by amethod suitable to the design; an example of a suitablemethod is given in Annex C.

5.2.8 Specification Sheet

A summary of the documents providing theinformation required in 5.2.2 shall be listed on aspecification sheet for each cylinder design. The title,reference number, revision numbers and dates oforiginal issue and version issues of each document shallbe given. All documents shall be signed or initialed bythe issuer. The specification sheet shall be given anumber and revision numbers if applicable, that canbe used to designate the cylinder design and shall carrythe signature of the engineer responsible for the design.Space shall be provided on the specification sheet fora stamp indicating registration of the design.

5.2.9 Additional Supporting Data

Additional data which would support the application,such as the service history of material proposed foruse, or the use of a particular cylinder design in otherservice conditions shall be provided, where applicable.

5.3 Type Approval Certificate

If the results of the design approval according to 5.2and the prototype testing according to 6.5 or 7.5 or 8.5as appropriate to the particular cylinder design aresatisfactory, the inspector shall foreword the test reportfor approval of the statutory authority.

6 REQUIREMENTS FOR METAL-LINEDHOOP WRAPPED CYLINDERS (CNG 2)

6.1 General

This standard does not provide design formula nor listpermissible stresses or strains, but requires theadequacy of the design to be established by appropriatecalculations and demonstrated by cylinders beingcapable of consistently passing the materials, designqualification, production and batch tests specified inthis standard.

During pressurization, this type of cylinder designexhibits behaviour in which the displacements of thecomposite overwrap and the metal liner are linearlysuperimposed. Due to different techniques of themanufacture, this standard does not give definitemethod for design.

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The design shall ensure a leakage-before-break failuremode under feasible degradation of pressure partsduring normal services. If leakage of the metal lineroccurs, it shall be only by the growth of a fatigue crack.

6.2 Materials

6.2.1 General Requirements

Material used shall be suitable for the serviceconditions specified in 4. The design shall ensure thatincompatible materials are not in contact.

6.2.2 Controls on Chemical Composition

6.2.2.1 Steel

Steel shall be aluminium and/or silicon-killed andproduced to pre-dominantly fine grain practice. Thechemical composition of all steel shall be declared anddefined by at least,

a) carbon, manganese, aluminium, and siliconcontents in all cases; and

b) chromium, nickel, molybdenum, boron andvanadium contents and that of any otheralloying elements intentionally added.

The sulphur and phosphorus content in the cast analysisshall not exceed the values given in Table 1.

Table 1 Maximum Sulphur and PhosphorusLimits in Steel

Tensile Strength < 950 MPa ≥ 950 MPa Sl No. Percent Percent (1) (2) (3) (4)

i) Level of sulphur 0.020 0.010 ii) Level of phosphorus 0.020 0.020

iii) Level of sulphur + phosphorus 0.030 0.025

6.2.2.2 Aluminium

Aluminium alloys may be used to produce linersprovided they meet all requirements of this standardand have maximum lead and bismuth contents notexceeding 0.003 percent.

6.2.3 Composite Materials

6.2.3.1 Resins

The material for impregnation may be thermosettingor thermoplastic resin. Examples of suitable matrixmaterials are epoxy, modified epoxy, polyester andvinylester thermosetting plastics, and polyethylene andpolyamide thermoplastic material.

The glass transition temperature of the resin materialshall be determined in accordance with ASTM D3418.

6.2.3.2 Fibres

Structural reinforcing filament material types shall be

glass fibre, aramid fibre or carbon fibre. If carbon fibrereinforcement is used, the design shall incorporatemeans to prevent galvanic corrosion of the metalliccomponents of the cylinder.

The manufacturer shall keep on file the publishedspecification for composite material, the materialmanufacturer’s recommendations for storage,conditions and shelf life and the materialmanufacturer’s certification that each shipmentconforms to said specification requirements.

The fibre manufacturer shall certify that the fibrematerial properties conform to the manufacturer’sspecification for the product.

6.3 Design Requirements

6.3.1 Test Pressure

The minimum test pressure used in manufacture shallbe 300 bar (1.5 times working pressure).

6.3.2 Burst Pressure and Fibre Stress Ratio

The metal liner shall have a minimum actual burstpressure of 260 bar.

The minimum actual burst pressure of the finishedcylinder shall be not less than the values given inTable 2. The composite overwrap shall be designedfor high reliability under sustained loading and cyclicloading. This reliability shall be achieved by meetingor exceeding the composite reinforcement stress ratiovalues given in Table 2. Stress ratio is defined as thestress in the fibre at the specified minimum burstpressure divided by the stress in the fibre at workingpressure. The burst ratio is defined as the actual burstpressure of the cylinder divided by the workingpressure. The stress ratio calculations shall includethe following:

a) An analysis method with capability for non-linear materials (special purpose computerprogramme or finite element analysisprogramme);

b) Correct modelling of the elastic-plastic stress-strain curve for a known liner material;

c) Correct modelling of the mechanicalproperties of composite material;

d) Calculations at auto-frettage pressure, zeropressure after auto-frettage, working pressureand minimum burst pressure;

e) Account for the prestresses from windingtension;

f) The minimum burst pressure, chosen such thatthe calculated stress at minimum burstpressure divided by the calculated stress at

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working pressure meets the stress ratiorequirements for the fibre used; and

g) Consideration of the load share between thedifferent fibres based on the different elasticmoduli of the fibres when analyzing cylinderswith hybrid reinforcement (two or moredifferent fibres). The stress ratio requirementsfor each individual fibre type shall be inaccordance with the values given in Table 2.

Verification of the stress ratios may also be performedusing strain gauges. An acceptable method is outlinedin Annex D.

Table 2 Minimum Actual Burst Values and StressRatios for Metal-Lined Hoop Wrapped

Cylinders (CNG 2)(Clauses 6.3.2 and 6.5.2.4)

Sl No.

Fibre Type Stress Ratio Burst Pressure

(bar) (1) (2) (3) (4)

i) Glass 2.75 5001) ii) Aramid 2.35 470

iii) Carbon 2.35 470 iv) Hybrid2) — —

1) Minimum actual burst pressure. In addition, calculations shall be performed in accordance with 6.3.2 to confirm that the minimum stress ratio requirements are also met.

2) Stress ratios and burst pressure shall be calculated in accordance with 6.3.2.

6.3.3 Stress Analysis

The stresses in the composite and in the liner afterprestress shall be calculated for 0 bar, 200 bar, testpressure and design burst pressure. The calculationsshall use suitable analysis techniques taking intoaccount non-linear material behaviour of the liner whenestablishing stress distributions.

For designs using auto-frettage to provide pre-stress,the limits within which the auto-frettage pressure shallfall and shall be calculated and specified. For designsusing controlled tension winding to provide prestress,the temperature at which it is performed, the tensionrequired in each layer of composite and the consequentprestress in the liner shall be calculated.

6.3.4 Maximum Defect Size

The maximum defect size at any location in the metalliner is such that the cylinder meets pressure cyclingand LBB requirements shall be specified. The NDEmethod shall be capable of detecting the maximumdefect size allowed.

The allowable defect size for NDE shall be determinedby an appropriate method, for example, as describedin Annex C.

6.3.5 Openings

Openings are permitted in heads only. The centre lineof openings shall coincide with the longitudinal axisof the cylinder.

6.3.6 Fire Protection

The cylinder design shall be protected with pressurerelief devices. The cylinder, its materials, pressure reliefdevices and any added protective material shall bedesigned collectively to ensure adequate safety duringfire conditions in the test specified in A-14. Amanufacturer may specify alternative PRD locationswhich shall be approved by statutory authority.Pressure relief devices shall be as per Gas CylinderRules, 2004.

6.4 Construction and Workmanship

6.4.1 General

The composite cylinder shall be manufactured from aseamless metallic liner overwrapped with continuousfilament windings. Fibre winding operations shall becomputer or mechanically controlled. The fibres shallbe applied under controlled tension during winding.After winding is completed, thermosetting resins shallbe cured by heating using a pre-determined andcontrolled time-temperature profile.

6.4.2 Liner

The manufacture of a metallic liner shall meet therequirements given in 6.2, 6.3.2 and either 6.5.2.2or 6.5.2.3 for the appropriate type of liner construction.

6.4.3 Neck Threads

The cylinder neck shall be threaded to suit the type ofvalves as given in IS 3224 or any other specificationas approved by the statutory authority. Threads shallbe clean cut, even, without chatter, answering togauges and concentric with the axis of the cylinder.

6.4.4 Overwrap

6.4.4.1 Fibre winding

The cylinders shall be manufactured by a fibre windingtechnique. During winding the significant variablesshall be monitored within specified tolerances anddocumented in a winding record. These variables caninclude but are not limited to,

a) fibre type including sizing;b) manner of impregnation;c) winding tension;d) winding speed;e) number of rovings;f) band width;g) type of resin and composition;

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h) temperature of the resin;j) temperature of the liner; andk) winding angle.

6.4.4.2 Curing of the thermosetting resins

If a thermosetting resin is used, the resin shall be curedafter filament winding. During the curing, the curingcycle (that is the time temperature history) shall bedocumented.

The maximum curing time and temperature forcylinders with aluminium alloy liners shall be belowthe time and temperature, which adversely affect metalproperties.

6.4.4.3 Auto-frettage

Auto-frettage, if used, shall be carried out before thehydrostatic pressure test. The auto-frettage pressureshall be within the limits established in 6.3.3 and themanufacturer shall establish the method of verifyingthe appropriate pressure.

6.4.5 Exterior Environmental Protection

The exterior of cylinders shall meet the requirementof the acid environment test described in A-13. Exteriorprotection may be provided by using any of thefollowing:

a) A surface finish giving adequate protection(for example, metal sprayed on to aluminium,anodizing); or

b) The use of a suitable fibre and matrix material(for example, carbon fibre in resin); or

c) A protective coating (for example, organiccoating, paint); if exterior coating is part ofthe design, the requirements of A-9 shall bemet; or

d) A covering impervious to the chemicals listedin A-14.

Any coatings applied to cylinders shall be such thatthe application process does not adversely affect themechanical properties of the cylinder. The coating shallbe designed to facilitate subsequent in-serviceinspection and the manufacturer shall provide guidanceon coating treatment during such inspection to ensurethe continued integrity of the cylinder.

Manufacturers are advised that an environmentalperformance test that evaluates the suitability of coatingsystems is provided in Annex E.

6.5 Prototype Testing Procedure


Prototype testing shall be conducted on each newdesign, on liners or finished cylinders, which are

representative of normal production and complete withidentification marks. The test liners or cylinders shallbe selected and the prototype tests detailed in 6.5.2witnessed by the inspector. If more cylinders or linersare subjected to the tests than are required by thisstandard, all results shall be documented.

6.5.2 Prototype Tests

6.5.2.1 Test required

In the course of the type approval, the inspector shallselect the necessary cylinders or liners for testing andwitness the following tests:

Liner material tests specified in 6.5.2.2 or 6.5.2.3

: As appropriate on 1 liner

Hydrostatic pressure burst test specified in 6.5.2.4

: On 1 liner and 3 cylinders

Ambient temperature pressuring cycling test specified in 6.5.2.5

: On 2 cylinders

LBB test specified in 6.5.2.6

: On 3 cylinders

Bonfire test specified in 6.5.2.7

: On 1 or 2 cylinders as appropriate

Penetration test specified in 6.5.2.8

: On 1 cylinder

Acid environment test specified in 6.5.2.9

: On 1 cylinder

Flaw tolerance test specified in 6.5.2.10

: On 1 cylinder

High temperature creep test specified in 6.5.2.11

: Where appropriate on 1 cylinder

Accelerated stress rupture test specified in 6.5.2.12

: On 1 cylinder

Extreme temperature pressure cycling test specified in 6.5.2.13

: On 1 cylinder

Resin shear strength test specified in 6.5.2.14

: On 1 sample coupon representative of the composite overwrap

6.5.2.2 Material tests for steel liners

Material tests shall be carried out on steel liners asfollows:

a) Tensile test — The material properties of thesteel in the finished liner shall be determinedin accordance with A-1 and shall meet therequirements therein.

b) Impact test — The impact properties of thesteel in the finished liner shall be determinedin accordance with A-2 and shall meet therequirements therein.

c) Sulphide stress cracking resistance test — Ifthe upper limit of the specified tensile strength

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for the steel exceeds 950 MPa, the steel froma finished cylinder shall be subjected to asulphide stress cracking resistance test inaccordance with A-3 and meet therequirements therein.

6.5.2.3 Material tests for aluminium alloy liners

Material tests shall be carried out on aluminium alloyliners as follows:

a) Tension test — The material properties of thealuminium alloy in the cylinder shall bedetermined in accordance with A-1 and shallmeet the requirements therein.

b) Corrosion test — Aluminum alloys shall meetthe requirement of the corrosion test carriedour in accordance with A-4.

c) Sustained load cracking tests — Aluminumalloys shall meet the requirements of thesustained load cracking test carried out inaccordance with A-5.

6.5.2.4 Hydrostatic pressure burst test

a) One liner shall be hydrostatically pressurizedto failure in accordance with A-11. The burstpressure shall exceed the minimum burstpressure specified for the liner design.

b) Three cylinders shall be hydrostaticallypressurized to failure in accordance withA-11. The burst pressure shall exceed theminimum burst pressure calculated by thestress analysis for the design, in accordancewith Table 2, and in no case be less than thevalue necessary to meet the stress ratiorequirements of 6.3.2.

6.5.2.5 Ambient temperature pressure cycling test

Two cylinders shall be pressure cycled to failure atambient temperature in accordance with A-12, or toa minimum of 45 000 cycles. The cylinders shallnot fail before reaching the specified service life inyears multiplied by 1 000 cycles. Cylindersexceeding 1 000 cycles multiplied by the specifiedservice life in years shall fail by leakage and not byrupture. Cylinders which do not fail within 45 000cycles shall be destroyed either by continuing thecycling until failure occurs, or by hydrostaticallypressurizing to burst. Cylinders exceeding 45 000cycles are permitted to fail by rupture. The numberof cycles to failure and the location of the failureinitiation shall be recorded.

6.5.2.6 Leak-before-break (LBB) test

The LBB test shall be carried out in accordancewith A-6 and shall meet the requirement therein.

6.5.2.7 Bonfire test

One or two cylinders as appropriate shall be tested inaccordance with A-14 and meet the requirementtherein.

6.5.2.8 Penetration test

One cylinder shall be tested in accordance with A-15and meet the requirement therein. An optionalenvironmental test is included in Annex E.

6.5.2.9 Acid environment test


6.5.2.10 Flaw tolerance test

One cylinder shall be tested in accordance with A-16and meet the requirement therein.

6.5.2.11 High temperature creep test

In designs, where the glass transition temperature ofthe resin does not exceed 102°C, one cylinder shall betested in accordance with A-17 and meet therequirements therein.

6.5.2.12 Accelerated stress rupture test

One cylinder shall be tested in accordance with A-18and meet the requirements therein.

6.5.2.13 Extreme temperature pressure cycling test


6.5.2.14 Resin shear strength

Resin material shall be tested in accordance with A-24and meet the requirements therein.

6.5.3 Change of Design

A design change is any change in the selection ofstructural materials or dimensional change notattributable to normal manufacturing tolerances. Minordesign changes shall be permitted to be qualifiedthrough a reduced test programme. Changes of designspecified in Table 3 shall require only the prototypetesting as specified in the table.

6.6 Batch Tests


Batch testing shall be conducted on finished cylinderswhich are representative of normal production and arecomplete with identification marks. The cylinders andliners required for testing shall be randomly selectedfrom each batch. If more cylinders are subjected to the

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Table 3 Change of Design for Metal-Lined-Hoop Wrapped Cylinders (CNG 2)(Clause 6.5.3)

Type of Test

Hydro-static Burst

Pressure Cycling at Ambient

Temperature

Bonfire

Penetra- Tion

Environ-mental

Flaw Tolerance

High Temper-

ature Creep

Stress Rupture

Sl No.

Design Change

See A-11 See A-12 See A-14 See A-15 See A-13 See A-16 See A-17 See A-18 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

i) Fibre manufacturer X X — — — — X X ii) Metallic liner material X X X X X X X X iii) Fibre material X X X X X X X X iv) Resin material — — — X X X X X v) Diameter change ≤ 20% X X — — — — — — vi) Diameter change >20% X X X X — X — — vii) Length

Change ≤50% X — X1) — — — — —

viii) Length Change >50%

X X X1) — — — — —

ix) Working pressure change ≤20%2)

X X — — — — — —

x) Dome shape X X — — — — — — xi) Opening size X X — — — — — — xii) Change in manufacturing

process X X — — — — — —

xiii) Pressure relief device — — X — — — — —

1) Test only required when length increases. 2) Only when thickness change proportional to diameter and/or pressure change.

tests than are required by this standard, all results shallbe documented. Where defects are detected inoverwrapping before any auto-frettage or hydrostaticpressure testing, the over wrapping may be completelyremoved and replaced.

6.6.2 Required Tests

6.6.2.1 At least the following tests shall be carried outon each batch of cylinders:

a) One hydrostatic pressure burst test on onecylinder in accordance with A-11. If the burstpressure is less than the minimum calculatedburst pressure, the procedures specified in 6.9shall be followed.

b) On a further cylinder, or liner, or heat treatedwitness sample representative of a finishedcylinder:1) A check of the critical dimensions against

the design (see 5.2.4.1);2) One tensile test in accordance with A-1;

the test result shall satisfy the requirementsof the design (see 5.2.4.1); and

3) For steel liners, three impact tests inaccordance with A-2; the test results shallsatisfy the requirements specified in A-2.

All cylinders or liners represented by a batch test whichfails to meet the specified requirements shall followthe procedures specified in 6.9.

6.6.2.2 Additionally, a periodic pressure cycling testshall be carried out on finished cylinders in accordancewith A-12 at a test frequency defined as follows:

a) Initially, one cylinder from each batch shallbe pressure cycled for a total of 1 000 timesthe specified service life in years, with aminimum of 15 000 cycles;

b) If on 10 sequential production batches of adesign family (that is similar material andprocess within the definition of a minordesign change (see 6.5.3), none of thepressure cycled cylinders in (a) leaks orruptures in less than 1 500 cycles multipliedby the specified life in years (minimum22 500 cycles) then the pressure cycle testmay be reduced to one cylinder from every5 batches of production;

c) If on 10 sequential production batches of adesign family, none of the pressure cycledcylinders in (a) leaks or rupture in less than2 000 cycles multiplied by the specifiedservices life in years (minimum 30 000cycles) then the pressure cycle test can bereduced to one cylinder from every 10 batchesof production;

d) Should more than 3 months have expiredsince the last pressure cycle test, then acylinder from the next batch of production

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shall be pressure cycle tested in order tomaintain the reduced frequency of batchtesting in (b) or (c);

e) should any reduced frequency pressure cycletest in (b) or (c) fail to meet the requirednumber of pressure cycles (minimum 22 500or 30 000 pressure cycles, respectively), thenit shall be necessary to repeat the batchpressure cycle test frequency in (a) for aminimum of 10 production batches in orderto re-establish the reduced frequency of batchpressure cycle testing in (b) or (c);

Should any cylinder in (a), (b) or (c) above failto meet the minimum cycle life requirement of1 000 cycles multiplied by the specified servicelife in years (minimum 15 000 cycles), then thecause of failure shall be determined andcorrected in accordance with the procedure in6.9. The pressure cycle test shall then berepeated on an additional three cylinders fromthat batch. Should any of the three additionalcylinders fail to meet the minimum pressurecycling requirement of 1 000 cycles multipliedby the specified service life in years, then thebatch shall be rejected.

6.7 Tests on Every Cylinder

Production examinations and tests shall be carried outas follows on all cylinders produced in batch. Non-destructive examinations shall be carried out inaccordance with a standard acceptable to the inspector.

Each cylinder shall be examined during manufactureand after completion as follows:

a) By NDE of metallic liners in accordance withAnnex B or demonstrated equivalent methodto verify that the maximum defect size doesnot exceed the size specified in the design asdetermined in accordance with 6.3.4. TheNDE method shall be capable of detectingthe maximum size allowed;

b) To verify that critical dimensions and massof the completed cylinders and of the linersand overwrapping are within designtolerances;

c) To verify compliance with specified surfacefinish with special attention to deep drawnsurfaces and folds or laps in the neck orshoulder of forged or spun end enclosures oropenings;

d) To verify the markings;e) By hardness tests of metallic liners in

accordance with A-8 carried out after the finalheat treatment. The values thus determined

shall be in the range of specified for thedesign; and

f) By hydraulic test of finished cylinders inaccordance with A-10.1. The manufacturershall establish the appropriate limit ofpermanent volumetric expansion for the testpressure used, but in no case shall thepermanent expansion exceed 5 percent of thetotal volumetric expansion measured underthe test pressure.

6.8 Batch Acceptance Certificate

If the results of batch testing according to 6.6 and 6.7are satisfactory, the manufacturer and the inspectorshall sign an acceptance certificate.

6.9 Failure to Meet Test Requirements

In the event of failure to meet test requirements,re-testing or re-heat treatment and re-testing shall becarried out as follows to the satisfaction of the inspector.

a) If there is evidence of a fault in carrying out atest, or an error of measurement, a further testshall be performed; if the result of this test issatisfactory, the first test shall be ignored;

b) If the test has been carried out in a satisfactorymanner, the cause of test failure shall beidentified as follows:

1) If the failure is considered to be due to theheat treatment applied, the manufacturermay subject all the liners implicated bythe failure to a further heat treatment, thatis, if the failure is in a test representingthe batch, test failure shall require re-heattreatment of all the represented cylindersprior to re-testing; however if the failureoccurs sporadically in a test applied toevery cylinder, then only those cylinderwhich fail the test shall require re-heattreatment and re-testing.i) Whenever liners are re-heat treated,

the minimum guaranteed wallthickness shall be maintained.

ii) Only the relevant batch test neededto prove the acceptability of the newbatch shall be performed again. Ifone or more tests prove evenpartially unsatisfactory, allcylinders of the batch shall berejected.

2) If the failure is due to a cause other thanthe heat treatment applied, all defectivecylinders shall be either rejected orrepaired by an approved method.Provided that the repaired cylinders pass

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the tests required for the repair, they shallbe re-instated as part of the originalbatch.

7 REQUIREMENTS FOR METAL-LINED FULLWRAPPED CYLINDERS (CNG 3)

7.1 General

This standard does not provide design formulae norlist permissible stresses or strain, but requires theadequacy of the design to be established byappropriate calculations and demonstrated by testingto show that cylinders are capable of consistentlypassing the materials, design qualification, productionand batch tests specified in this standard.

During pressurization, this type of cylinder exhibitsbehavior in which the displacements of the compositeoverwrap and the liner are superimposed. Due todifferent techniques of manufacture, this standard doesnot give a definite method for design.

The design shall ensure a leakage-before-break failuremode under feasible degradation of pressure partsduring normal service. If leakage of the metal lineroccurs, it shall be only by the growth of a fatigue crack.

7.2 Materials


Materials used shall be suitable for the serviceconditions specified in 4. The design shall ensure thatincompatible materials are not in contact.

7.2.2 Controls on Chemical Composition

7.2.2.1 Steel

Steel shall be aluminum and/or silicon-killed andproduced to predominantly fine grain practice. Thechemical composition of all steels shall be declaredand defined by at least:

a) Carbon, manganese, aluminium, and siliconcontents in all cases; and

b) Chromium, nickel, molybdenum, boron andvanadium contents, and that of any otheralloying elements intentionally added.

The sulphur and phosphorus content in the castanalysis shall not exceed the values in Table 4.

Table 4 Maximum Sulphur andPhosphorus Limits

Tensile Strength < 950 MPa ≥ 950 MPa Sl No. Percent Percent (1) (2) (3) (4)

i) Level of sulphur 0.020 0.010 ii) Level of phosphorus 0.020 0.020 iii) Level of sulfur +

phosphorus 0.030 0.025

7.2.2.2 Aluminium

Aluminium alloys may be used to produce linersprovided they meet all requirements of this standardand have maximum lead and bismuth contents notexceeding 0.003 percent.

7.2.3 Composite Materials

7.2.3.1 Resin



7.2.3.2 Fibres

Structural reinforcing filament material types shall beglass fibre, aramid fibre or carbon fibre. If carbon fibrereinforcement is used the design shall incorporatemeans to prevent galvanic corrosion of the metalliccomponents of the cylinder.

The manufacturer shall keep on file the publishedspecification for composite material, the materialmanufacturer’s recommendations for storage, conditionsand shelf life and the material manufacturer’scertification that each shipment conforms to saidspecification requirements.

The fibre manufacturer shall certify that the fibrematerial properties conform to the manufacturer’sspecifications for the product.


7.3.1 Test Pressure


7.3.2 Burst Pressure and Fibre Stress Ratios

The minimum actual burst pressure shall be not lessthan the values given in Table 5. The compositeoverwrap shall be designed for high reliability undersustained loading and cyclic loading. This reliabilityshall be achieved by meeting or exceeding thecomposite reinforcement stress ratio values given inTable 5. Stress ratio is defined as the stress in the fibreat the specified minimum burst pressure divided bythe stress in the fibre at working pressure. The burstratio is defined as the actual burst pressure of thecylinder divided by the working pressure.

The stress ratio calculations shall include:

a) an analysis method with capability for non-linear materials (special purpose computer

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programme or finite element analysisprogramme);

b) correct modelling of the elastic-plastic stress-strain curve for a known liner material;

c) correct modelling of the mechanicalproperties of composite material;

d) calculations at auto-frettage pressure, zeropressure after auto-frettage, working pressureand minimum burst pressure;

e) account for the pre-stresses from windingtension;

f) minimum burst pressure, chosen such that thecalculated stress at minimum burst pressuredivided by the calculated stress at workingpressure meets the stress ratio requirementsfor the fibre used; and

g) consideration of the load share between thedifferent fibres based on the different elasticmoduli of the fibres when analyzing cylinderswith hybrid reinforcement (two or moredifferent fibres). The stress ratio requirementsfor each individual fibre type shall be inaccordance with the values given in Table 5.

Verification of the stress ratios may also be performedusing strain gauges. An acceptable method is outlinedin Annex D.

Table 5 Minimum Actual Burst Values andStress Ratios for Metal-Lined Full

Wrapped Cylinders (CNG 3)

Sl No.

Fibre Type Stress Ratio Burst Pressure, bar

(1) (2) (3) (4)

i) Glass 3.65 7001) ii) Aramid 3.10 600

iii) Carbon 2.35 470

iv) Hybrid2) — —

1) Minimum actual burst pressure. In addition, calculations shall be performed in accordance with 7.3.2 to confirm that the minimum stress ratio requirements are also met.

2) Stress ratios and burst pressure shall be calculated in accordance with 7.3.2.


A stress analysis shall be performed to justify theminimum design wall thicknesses. It shall include thedetermination of the stresses in liners and fibres ofcomposite designs. The stresses in the tangential andlongitudinal direction of the cylinder in the compositeand in the liner after pre-stress shall be calculated for0 bar, 200 bar, test pressure and design burst pressure.The calculations shall use suitable analysis taking intoaccount non-linear material behaviour of the liner whenestablishing stress distributions. The limits within

which the auto-frettage pressure shall fall shall becalculated.

7.3.4 Maximum Defect Size

The maximum defect size at any location in the metalliner such that the cylinder meets pressure cycling andLBB requirements shall be specified. The NDE methodshall be capable of detecting the maximum defect sizeallowed.

The allowable defect size for NDE shall be determinedby an appropriate method (see Annex C).

7.3.5 Openings

Openings are permitted in heads only. The centre lineof openings shall coincide with the longitudinal axisof the cylinder.


The cylinder design shall be protected with pressurerelief devices. The cylinder, its materials, pressure reliefdevices and any protective material shall be designedcollectively to ensure adequate safety during fireconditions in the test specified in A-14. A manufacturermay specify alternative PRD locations for specificvehicle installations in order to optimize safetyconsiderations. Pressure relief devices shall beapproved as per Gas Cylinder Rules, 2004.


7.4.1 General

The composite cylinder shall be manufactured from aseamless metallic liner overwrapped with continuousfilament windings. Fibre winding operations shall becomputer or mechanically controlled. The fibres shallbe applied under controlled tension during winding.After winding is complete, thermosetting resins shallbe cured by heating, using a predetermined andcontrolled time-temperature profile.

7.4.2 Liner

The manufacture of a metallic liner shall meet therequirements given in 7.2, 7.3.2 and either 7.5.2.2or 7.5.2.3 for the appropriate type of liner construction.

7.4.3 Neck Threads

The cylinder neck shall be threaded to suit the type ofvalves as given in IS 3224 or any other specificationas approved by the statutory authority. Threads shallbe clean cut, even, without chatter, answering to gaugesand concentric with the axis of the cylinder.

7.4.4 Over wrap

7.4.4.1 Fibre winding

The cylinders shall be manufactured by a fibre winding

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technique. During winding the significant variablesshall be monitored within specified tolerances anddocumented in a winding record. These variables caninclude but are not limited to:

a) Fibre type including sizing;b) Manner of impregnation;c) Winding tension;d) Winding speed;e) Number of rovings;f) Band width;g) Type of resin and composition;h) Temperature of the resin;j) Temperature of the liner; andk) Winding angle.

7.4.4.2 Curing of the thermosetting resins

If a thermosetting resin is used, the resin shall be curedafter filament winding. During curing, the curing cycle(that is, the time temperature history) shall bedocumented.

The maximum curing time and temperature forcylinders with aluminium alloy liners shall be belowthe time and temperature, which adversely affect metalproperties.

7.4.4.3 Auto-frettage

Auto-frettage, if used, shall be carried out before thehydrostatic pressure test. The auto-frettage pressureshall be within the limits established in 7.3.3 and themanufacturer shall establish the method of verifyingthe appropriate pressure.


The exterior of cylinders shall meet the requirementof the acid environment test described in A-13. Exteriorprotection may be provided by using any of thefollowing:

a) A surface finish giving adequate protection(for example metal sprayed on to aluminum,anodizing); or

b) The use of a suitable fibre and matrix material(for example carbon fibre in resin); or

c) A protective coating (for example organiccoating, paint); if exterior coating is part ofthe design, the requirements of A-9 shall bemet; or

d) A covering impervious to the chemicals listin A-14.

Any coatings applied to cylinders shall be such thatthe application process does not adversely affect themechanical properties of the cylinder. The coating shallbe designed to facilitate subsequent in-service

inspection and the manufacturer shall provide guidanceon coating treatment during such inspection to ensurethe continued integrity of the cylinder.




Prototype testing shall be conducted on each newdesign, on finished cylinders, which are representativeof normal production and complete with identificationmarks. The test cylinders or liners shall be selectedand the prototype tests detailed in 7.5.2 witnessed bythe inspector. If more cylinders or liners are subjectedto the tests than are required by this standard, all resultsshall be documented.




Liner material tests specified in 7.5.2.2 or 7.5.2.3

: As appropriate on 1 liner

Hydrostatic pressure burst test specified in 7.5.2.4

: On 3 cylinders


: On 2 cylinders

LBB test specified in 7.5.2.6 : On 3 cylinders Bonfire test specified in 7.5.2.7

: On 1 or 2 cylinders as appropriate

Penetration test specified in 7.5.2.8

: On 1 cylinder

Acid environment test specified in 7.5.2.9

: On 1 cylinder


: On 1 cylinder


: Where appropriate on 1 cylinder


: On 1 cylinder


: On 1 cylinder



Drop test specified in 7.5.2.15

: On 1 cylinder

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IS 15935 : 2011

7.5.2.2 Material tests for steel liners

Material tests shall be carried out on steel liners asfollows:

a) Tensile test — The material properties of thesteel in the finished liner shall be determinedin accordance with A-1 and shall meet therequirements therein.

b) Impact test — The impact properties of thesteel in the finished liner shall be determinedin accordance with A-2 and shall meet therequirements therein.

c) Sulphide stress cracking resistance test — Ifthe upper limit of the specified tensile strengthfor the steel exceeds 950 MPa, the steel froma finished cylinder shall be subjected to asulphide stress cracking resistance test inaccordance with A-3 and meet therequirements therein.

7.5.2.3 Material tests for aluminium alloy liner

Material tests shall be carried out on aluminium alloyliners as follows:

a) Tension test — The material properties of thealuminium alloy in the cylinder shall bedetermined in accordance with A-1 and shallmeet the requirements therein.

b) Corrosion test — Aluminum alloys shall meetthe requirement of the corrosion test carriedout in accordance with A-4.

c) Sustained load cracking tests — Aluminumalloys shall meet the requirements of thesustained load cracking test carried out inaccordance A-5.


Three cylinders shall be hydrostatically pressurized tofailure in accordance with A-11. The cylinder burstpressure shall exceed the specified minimum burstpressure established by the stress analysis for the designin accordance with Table 5 and in no case be less thanthe value necessary to meet the stress ratio requirementsof 7.3.2.


Two cylinders shall be pressure cycled to failure atambient temperature in accordance with A-12, or to aminimum of 45 000 cycles. The cylinders shall notfail before reaching the specified service life in yearsmultiplied by 1 000 cycles. Cylinders exceeding 1 000cycles multiplied by the specified service life in yearsshall fail by leakage and not by rupture. Cylinderswhich do not fail within 45 000 cycles shall bedestroyed either by continuing the cycling until failureoccurs, or by hydrostatically pressurizing to burst.

Cylinders exceeding 45 000 cycles are permitted tofail by rupture. The number of cycles to failure andthe location of the failure initiation shall be recorded.




One or two cylinders as appropriate shall be tested inaccordance with A-14 and meet the requirement therein.








In designs, where the glass transition temperature ofthe resin does not exceed 102°C, one cylinder shall betested in accordance with A-17 and meet therequirements therein.






Resin material shall be tested in accordance with A-24,and meet the requirements therein.

7.5.2.15 Drop test

One (or more) finished cylinders shall be drop tested inaccordance with A-19 and meet the requirements therein.


A design change is any change in the selection ofstructural materials or dimensional change notattributable to normal manufacturing tolerances.

Minor design changes shall be permitted to be qualifiedthrough a reduced test programme. Changes of designspecified in Table 6 shall require design qualificationtesting as specified in Table 6.

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7.6 Batch Tests


Batch testing shall be conducted on finished cylinderswhich are representative of normal production and arecomplete with identification marks. The cylinders andliner required for testing shall be randomly selectedfrom each batch. If more cylinders are subjected to thetests than are required by this standard, all results shallbe documented. Where defects are detected in overwrapping before any auto-frettage or hydrostaticpressure testing, the overwrapping may be completelyremoved and replaced.



a) One hydrostatic pressure burst test on onecylinder in accordance with A-11. If the burstpressure is less than the minimum calculatedburst pressure, the procedures specified in 7.9shall be followed.

b) On a further cylinder, or liner, or heat treatedwitness sample representative of a finishedcylinder:1) A check of the critical dimensions against

the design (see 5.2.4.1);2) One tensile test in accordance with A-1;

the test result shall satisfy the require-ments of the design (see 5.2.4.1); and

Table 6 Change of Design for Metal-Lined Full Wrapped Cylinders (CNG 3)(Clause 7.5.3)

Type of Test

Hydrostatic Burst

Pressure Cycling at Ambient

Temperature

Bonfire Penetra-tion

Environ-mental

Flaw Tolerance

High Temperature

Creep

Stress Rupture

Drop

Sl No.

Design Change

See A-11 See A-12 See A-14 See A-15 See A-13 See A-16 See A-17 See A-18 See A-19 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

i) Fibre manufacturer X X — — — — X X X ii) Metallic liner material X X X X X X X X X

iii) Fibre material X X X X X X X X X iv) Resin material — — — X X X X X X v) Diameter change ≤ 20% X X — — — — — — —

vi) Diameter change > 20% X X X X — X — — X vii) Length change ≤ 50% X — X1) — — — — — —

viii) Length change > 50% X X X1) — — — — — X ix) Working pressure

change ≤ 20%2) X X — — — — — — —

x) Dome shape X X — — — — — — — xi) Opening size X X — — — — — — —

xii) Change in manufacturing process

X X — — — — — — —

xiii) Pressure relief device — — X — — — — — —


3) For steel liners, three impact tests inaccordance A-2; the test results shallsatisfy the requirements specified in A-2.



a) Initially, one cylinder from each batch shallbe pressure cycled for a total of 1 000 timesthe specified service life in years, with aminimum of 15 000 cycles;

b) If on 10 sequential production batches of adesign family (that is similar material andprocess within the definition of a minor designchange, see 7.5.3), none of the pressure cycledcylinders in (a) leaks or ruptures in less than1 500 cycles multiplied by the specified lifein years (minimum 22 500 cycles) then thepressure cycle test may be reduced to onecylinder from every 5 batches of production;

c) If on 10 sequential production batches of adesign family, none of the pressure cycledcylinders in (a) leaks or rupture in less than2 000 cycles multiplied by the specifiedservices life in years (minimum 30 000 cycles)then the pressure cycle test can be reduced toone cylinder from every 10 batches ofproduction;

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d) Should more than 3 months have expiredsince the last pressure cycle test, then acylinder from the next batch of productionshall be pressure cycle tested in order tomaintain the reduced frequency of batchtesting in (b) or (c); and

e) Should any reduced frequency pressure cycletest in (b) or (c) fail to meet the requirednumber of pressure cycles (minimum 22 500or 30 000 pressure cycles, respectively), thenit shall be necessary to repeat the batchpressure cycle test frequency in (a) for aminimum of 10 production batches in orderto re-establish the reduced frequency of batchpressure cycle testing in (b) or (c).

Should any cylinder in (a), (b) or (c) fail to meet theminimum cycle life requirement of 1 000 cyclesmultiplied by the specified service life in years(minimum 15 000 cycles), then the cause of failure shallbe determined and corrected in accordance with theprocedure given in 7.9. The pressure cycle test shallthen be repeated on an additional three cylinders fromthat batch. Should any of the three additional cylindersfail to meet the minimum pressure cycling requirementof 1 000 cycles multiplied by the specified service lifein years, then the batch shall be rejected.


Production examinations and tests shall be carried outas follows on all cylinders produced in batch. Non-destructive examinations shall be carried out inaccordance with a standard acceptable to the inspector.

Each cylinder shall be examined during manufactureand after completion as follows:

a) By NDE of metallic liners in accordance withAnnex B or demonstrated equivalent methodto verify that the maximum defect size doesnot exceed the size specified in the design asdetermined in accordance with 7.3.4. TheNDE method shall be capable of detecting themaximum size allowed;

b) To verify that critical dimensions and mass ofthe completed cylinders and of the liners andover wrapping are within design tolerances;

c) To verify compliance with specified surfacefinish with special attention to deep drawnsurfaces and folds or laps in the neck or shoulderof forged or spun end enclosures or openings;

d) To verify the markings;e) By hardness tests of metallic liners in

accordance with A-8 carried out after the finalheat treatment. The values thus determinedshall be in the range of specified for the design;and

f) By hydraulic test of finished cylinders inaccordance with A-10.1. The manufacturershall establish the appropriate limit ofpermanent volumetric expansion for the testpressure used, but in no case shall thepermanent expansion exceed 5 percent of thetotal volumetric expansion measured underthe test pressure.




In the event of failure to meet test requirements, re-testing or re-heat treatment and re-testing shall be carriedout as follows to the satisfaction of the inspector;


b) If the test has been carried out in a satisfactorymanner, the cause of test failure shallbe identified.1) If the failure is considered to be due to

the heat treatment applied, themanufacturer may subject all thecylinders implicated by the failure to afurther heat treatment, that is, if thefailure is in a test representing the batchcylinders, test failure shall require re-heattreatment of all the represented cylindersprior to re-testing; however if the failureoccurs sporadically in a test applied toevery cylinder, then only those cylinderwhich fail the test shall require re-heattreatment and re-testing.i) Whenever liners are re-heat treated,

the minimum guaranteed wallthickness shall be maintained.

ii) Only the relevant batch test neededto prove the acceptability of the newbatch shall be performed again. Ifone or more tests prove evenpartially unsatisfactory, all cylindersof the batch shall be rejected.

2) If the failure is due to a cause other thanthe heat treatment applied, all defectivecylinders shall be either rejected orrepaired by an approved method.Provided that the repaired cylinders passthe tests required for the repair, they shallbe re- instated as part of the original batch.

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IS 15935 : 2011

8 REQUIREMENTS FOR NON-METAL-LINEDCOMPOSITE CYLINDERS (CNG 4)

8.1 General

This standard does not provide design formulae norlist permissible stresses or strain, but requires theadequacy of the design to be established by appropriatecalculations and demonstrated by testing to show thatcylinders are capable of consistently passing thematerials, design qualification, production and batchtests specified in this standard.

The design shall ensure a leakage-before-break failuremode under feasible degradation of pressure partsduring normal service.

8.2 Materials


Materials used shall be suitable for the serviceconditions specified in 4. The design shall ensure thatincompatible materials are not in contact.

8.2.2 Resins



8.2.3 Fibres

Structural reinforcing filament material types shall beglass fibre, aramid fibre or carbon fibre. If carbon fibrereinforcement is used the design shall incorporatemeans to prevent galvanic corrosion of the metalliccomponents of the cylinder.

The manufacturer shall keep on file the publishedspecification for composite material, the materialmanufacturer’s recommendations for storage, conditionsand shelf life and the material manufacturer’scertification that each shipment conforms to saidspecification requirements.

The fibre manufacturer shall certify that the fibrematerial properties conform to the manufacturer’sspecification for the product.

8.2.4 Plastic Liners

The polymeric material shall be compatible with theservice conditions specified in 4.

8.2.5 Metal End Bosses

The metal end bosses connected to the non-metallicliner shall be of a material compatible with the serviceconditions specified in 4.


8.3.1 Test Pressure


8.3.2 Burst Pressure and Fibre Stress Ratios

The minimum actual burst pressure shall be not lessthan the values given in Table 7. The compositeoverwrap shall be designed for high reliability undersustained loading and cyclic loading. This reliabilityshall be achieved by meeting or exceeding thecomposite reinforcement stress ratio values given inTable 7. Stress ratio is defined as the stress in the fibreat the specified minimum burst pressure divided bythe stress in the fibre at working pressure. The burstratio is defined as the actual burst pressure of thecylinder divided by the working pressure. For non-metal lined full wrapped designs, the stress ratio isequal to the burst ratio. Verification of the stress ratiosmay also be performed using strain gauges. Anacceptable method is outlined in Annex D.

Table 7 Minimum Actual Burst Values and StressRatios for Non-metal-Lined Full Wrapped

Cylinders (CNG 4)(Clauses 8.3.2 and 8.5.2.3)

Sl No.

Fibre Type Stress Ratio Burst Pressure, bar

(1) (2) (3) (4) i) Glass 3.65 730

ii) Aramid 3.10 620 iii) Carbon 2.35 470 iv) Hybrid1)

1) Stress ratios and burst pressures shall be calculated in accordance with 8.3.2.


A stress analysis shall be performed to justify theminimum design wall thicknesses. It shall include thedetermination of the stresses in liners and fibres ofcomposite designs.

The stresses in the tangential and longitudinal directionof the cylinder composite and in the liner shall becalculated. The pressure used for these calculationsshall be 0 bar, 200 bar, test pressure and design burstpressure. The calculations shall use suitable analysistechniques to establish stress distribution throughoutthe cylinder.

8.3.4 Openings

Openings are permitted in the end bosses only. Thecentre line of openings shall coincide with thelongitudinal axis of the cylinder.


The cylinder design shall be protected with pressure

19

IS 15935 : 2011

relief devices. The cylinder, its materials, pressure reliefdevices and any protective material shall be designedcollectively to ensure adequate safety during fireconditions in the test specified in A-14. A manufacturermay specify alternative PRD locations for specificvehicle installations in order to optimize safetyconsiderations. Pressure relief devices shall be approvedas per Gas Cylinder Rules, 2004.


8.4.1 General

The composite cylinder shall be manufactured from anon-metallic liner overwrapped with continuousfilament windings. Fibre winding operations shall becomputer or mechanically controlled. The fibre shallbe applied under controlled tension during winding.After winding is complete, thermosetting resins shallbe cured by heating, using a predetermined andcontrolled time-temperature profile.

8.4.2 Neck Threads

The cylinder neck shall be threaded to suit the type ofvalves as given in IS 3224 or any other specificationas approved by the statutory authority. Threads shallbe clean cut, even, without surface discontinuities andconcentric with the axis of the cylinder.

8.4.3 Curing of the Thermosetting Resins

The curing temperature for thermosetting resin shallbe at least 10°C below the softening temperature ofthe plastic liner.


The exterior of cylinders shall meet the requirement ofthe acid environment test described in A-13. Exteriorprotection may be provided by using any of the following:

a) A surface finish giving adequate protection(for example, metal sprayed on to aluminum,anodizing); or

b) The use of a suitable fibre and matrix material(for example, carbon fibre in resin); or

c) A protective coating (for example, organiccoating, paint); if exterior coating is part of thedesign, the requirements of A-9 shall be met; or

d) A covering impervious to the chemicals listin A-14.

Any coatings applied to cylinders shall be such thatthe application process does not adversely affect themechanical properties of the cylinder. The coating shallbe designed to facilitate subsequent in-serviceinspection and the manufacturer shall provide guidanceon coating treatment during such inspection to ensurethe continued integrity of the cylinder.



8.5.1 General

Prototype testing shall be conducted on each newdesign, on finished cylinders, which are representativeof normal production and complete with identificationmarks. The test cylinder or liners shall be selected andthe prototype tests detailed in 8.5.2 witnessed by theinspector. If more cylinders or liners are subjected tothe tests than are required by this standard, all resultsshall be documented.




Liner material tests specified in 8.5.2.2 : On 1 liner Hydrostatic pressure burst test specified in 8.5.2.3

: On 3 cylinders


: On 2 cylinders

LBB test specified in 8.5.2.5 : On 3 cylinders

Bonfire test specified in 8.5.2.6 : On 1 or 2 cylinders as appropriate

Penetration test specified in 8.5.2.7 : On 1 cylinder Acid environment test specified in 8.5.2.8

: On 1 cylinder


: On 1 cylinder


: On 1 cylinder as appropriate


: On 1 cylinder


: On 1 cylinder



Drop test specified in 8.5.2.14 : On at least 1 cylinder

Boss torque test specified in 8.5.2.15 : On 1 cylinder Permeation test specified in 8.5.2.16 : On 1 cylinder Natural gas cycling test specified in 8.5.2.17

: On 1 cylinder

8.5.2.2 Material tests for plastic liners

The tensile yield strength and ultimate elongation shall

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IS 15935 : 2011

be determined in accordance with A-21 and shall meetthe requirements therein.

The softening temperature shall be determined inaccordance with A-22 and shall meet the requirementstherein.


Three cylinders shall be hydrostatically pressurized tofailure in accordance with A-11. The cylinder burstpressure shall exceed the specified minimum burstpressure established by the stress analysis for the linerdesign, in accordance with Table 7, and in no case lessthan the value necessary to meet the stress ratiorequirements of 8.3.2.


Two cylinders shall be pressure cycle tested at ambienttemperature in accordance with A-12 to failure, or to aminimum of 45 000 cycles. The cylinders shall notfail before reaching the specified service life in yearsmultiplied by 1 000 cycles. Cylinders exceeding 1 000cycles multiplied by the specified service life in yearsshall fail by leakage and not by rupture. Cylinderswhich do not fail within 45 000 cycles shall bedestroyed either by continuing the cycling until failureoccurs, or by hydrostatically pressurizing to burst.Cylinders exceeding 45 000 cycles are permitted tofail by rupture. The number of cycles to failure andthe location of the failure initiation shall be recorded.




One or two cylinders as appropriate shall be tested inaccordance with A-14 and meet the requirementtherein.














Resin material shall be tested in accordance with A-24,and meet the requirements therein.

8.5.2.14 Drop test

One (or more) finished cylinders shall be drop testedin accordance with A-19 and meet the requirementstherein.

8.5.2.15 Boss torque test


8.5.2.16 Permeation test

One cylinder shall be tested for permeation inaccordance with A-20 and meet the requirementstherein.

8.5.2.17 Natural gas cycling test



A design change is any change in the selection ofstructural materials or dimensional change notattributable to normal manufacturing tolerances.

Minor design changes shall be permitted to be qualifiedthrough a reduced test programme. Changes of designspecified in Table 8 shall require design qualificationtesting as specified in Table 8.

8.6 Batch Tests


Batch testing shall be conducted on finished cylinderswhich are representative of normal production and arecomplete with identification marks. The cylinders andliners required for testing shall be randomly selectedfrom each batch. If more cylinders are subjected to thetests than are required by this standard, all results shallbe documented.



a) On one cylinder, a hydrostatic pressure bursttest is carried out in accordance with A-11. If

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IS 15935 : 2011

Table 8 Change of Design for Non-metal-Lined Full Wrapped Cylinders (CNG 3)(Clause 8.5.3)

Type of Test

Hydro-static Burst

Pressure Cycling

at Ambient Tempera-

ture

Bonfire Penetra-tion

Environ-mental

Flaw Toler-ance

High Tempera-

ture Creep

Stress Rupture

Drop Boss Torque

Perme-ation

CNG Cycling

Sl No.

Design Change

See A-11

See A-12

See A-14

See A-15

See A-13

See A-16

See A-17

See A-18

See A-19

See A-23

See A-20

See A-25

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

i) Fibre manufacturer X X — — — — X X X X X X ii) Plastic liner X X X X X X X X X X X X

iii) Fibre material X X X X X X X X X X X X iv) Resin material — — — X X X X X X — — — v) Diameter change ≤ 20% X X — — — — — — — — — —

vi) Diameter change >20% X X X X — X — — X — — — vii) Length change ≤50% X — X1) — — — — — — — — —

viii) Length change >50% X X X1) — — — — — X — — — ix) Working pressure

change ≤ 20%2) X X — — — — — — — — — —

x) Dome shape X X — — — — — — — X X X xi) Opening size X X — — — — — — — — — —

xii) End boss design — — — — — — — — — X X X xiii) Change in

manufacturing process X X — — — — — — — — — —

xiv) Pressure relief device — — X — — — — — — — — —


the burst pressure is less than the minimumcalculated burst pressure, the proceduresspecified in 8.9 shall be followed.

b) On a further cylinder or liner or witnesssample representative of a finished cylinder:1) A check of the critical dimensions against

the design (see 5.2.4.1);2) One tensile test of the plastic liner in

accordance with A-21; the test result shallsatisfy the requirements of the design (see5.2.4.1); and

3) The melt temperature of the plastic linershall be tested in accordance with A-22;and meet the requirements of the design.



a) Initially, on one cylinder from each batch theend boss shall be torque tested in accordancewith A-23. The cylinder shall then be pressurecycled for a total of 1 000 times the specifiedservice life in years, with a minimum of

15 000 cycles. Following the requiredpressure cycling, the cylinder shall be leaktested in accordance with the methoddescribed in A-9, and meet the requirementstherein;

b) If on 10 sequential production batches of adesign family (that is similar material andprocess within the definition of a minordesign change) (see 8.5.3), none of thepressure cycled cylinders in (a) leaks orruptures in less than 1 500 cycles multipliedby the specified life in years (minimum 22500 cycles) then the pressure cycle test maybe reduced to one cylinder from every 5batches of production;

c) If on 10 sequential production batches of adesign family, none of the pressure cycledcylinders in (a) leaks or rupture in less than2 000 cycles multiplied by the specifiedservices life in years (minimum 30 000 cycles)then the pressure cycle test can be reduced toone cylinder from every 10 batches ofproduction;

d) Should more than 3 months have expiredsince the last pressure cycle test, then acylinder from the next batch of production

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IS 15935 : 2011

shall be pressure cycle tested in order tomaintain the reduced frequency of batchtesting in (b) or (c); and

e) Should any reduced frequency pressure cyclecylinder in (b) or (c) fail to meet the requirednumber of pressure cycles (minimum 22 500or 30 000 pressure cycles, respectively), thenit shall be necessary to repeat the batchpressure cycle test frequency in (a) for aminimum of 10 production batches in orderto re-establish the reduced frequency of batchpressure cycle testing in (b) or (c).

Should any cylinder in (a), (b) or (c) fail to meet theminimum cycle life requirement of 1 000 cyclesmultiplied by the specified service life in years(minimum 15 000 cycles), then the cause of failureshall be determined and corrected following theprocedures in 8.9. The pressure cycle test shall then berepeated on an additional three cylinders from thatbatch. Should any of the three additional cylinders failto meet the minimum pressure cycling requirement of1 000 cycles multiplied by the specified service life inyears, then the batch shall be rejected.


Production examinations and tests shall be carried outas follows on all cylinders produced in batch. Eachcylinder shall be examined during manufacture andafter completion as follows:

a) By inspection of liners to confirm that themaximum defect size present is smaller thanthe specified in the design;

b) To verify that critical dimensions and massof the completed cylinders and of any linerand overwrapping are within designtolerances;

c) To verify compliance with specified surfacefinish.

d) To verify the markings;e) By hydraulic test of finished cylinders in

accordance with A-10.1. The manufacturershall define the appropriate limit of elasticexpansion for the test pressure used, but inno case shall the elastic expansion of anycylinder exceed the average batch value bymore than 10 percent; and

f) By leak test in accordance with A-9, and shallmeet the requirements therein.




In the event of failure to meet test requirements, re-testing shall be carried out as follows:


b) If the test has been carried out in a satisfactorymanner, the cause of test failure shall beidentified by the following:1) All defective cylinders shall be rejected

or repaired by an approval method.Provided that the repaired cylinders passthe test(s) required for the repair, theyshall be re-instated as part of the originalbatch.

2) The new batch shall be re-tested. All therelevant prototype or batch test needed toprove the acceptability of the new batchshall be performed again. If one or moretests prove even partially unsatisfactory,all cylinders of the batch shall be rejected.

9 MARKING

On each cylinder the manufacturer shall provide clearpermanent markings not less than 6 mm high. Markingshall be made either by labels incorporated into resincoatings, labels attached by adhesive or anycombination of the above. Multiple labels are allowedand should be located such that they are not obscuredby mounting brackets.

Each cylinder complying with this standard shall bemarked as follow:

a) The words ‘CNG only’;b) The words ‘DO NOT USE AFTER XX/

XXXX’, where XX/XXXX identifies themonth and year of expiry. The period betweenthe dispatch date and the expiry date shall notexceed the specified service life. The expirydate may be applied to the cylinder at the timeof dispatch, provided that the cylinders havebeen stored in a dry location without internalpressure;

c) Manufacturer’s identification;d) Cylinder identification (a serial number

unique for every cylinder);e) Working pressure at temperature;f) Reference to this standard, along with cylinder

type and statutory authority’s approvalnumbers;

g) The words ‘Use only an approvedmanufacturer’s PRD’;

23

IS 15935 : 2011

h) Date of manufacture (month and year);j) Periodical retesting on XX – XX – XXXX;k) Expiry date; andm) When labels are used, a unique identification

number and the manufacturer’s identificationstumped on an exposed metal surface topermit tracing in the event that the label isdestroyed.

The marking shall be placed in the listed sequence butthe specific arrangement may be varied to match thespace available. An acceptable example is:

CNG onlyDo not use after 3/2009Manufacturer/Identification number200 bar/15°CIS 15935 : 2011 CNG-2 (registration No.)‘Use only BIS-Approved PRD’Manufacturer date 08/98Warning: Vehicles with CNG 4 cylinder shall

not be parked in enclosed space for

extended periods of time.Permention of gas through thecylinder wall or leakage between theend connections and the liner shallbe considered in the design.

10 PRIOR TO DISPATCH

Preparation of dispatch from the manufacturer’s shop,every cylinder shall be internally cleaned and dried.Cylinders which are not immediately closed by thefitting of a valve, and safety devices if applicable, shallhave plugs, which will prevent entry of moisture andprotect threads, fitted to all openings. A corrosioninhibitator (for example oil-containing) shall besprayed into all steel liners prior to dispatch.

The manufacturer’s statement of service and allnecessary information and instructions to ensure theproper handling, use and in-service inspection of thecylinder shall be supplied to the purchaser. Thestatement of service shall be in accordance with 5.2.3.Guidance on the content of the instructions is given inAnnex F.

ANNEX A(Clauses 5.1, 6.3.6, 6.4.5, 6.5.2.2, 6.5.2.6, 6.5.2.7 to 6.5.2.14, 6.6.2.1, 6.6.2.2, 6.7,

7.3.6, 7.4.4.4, 7.5.2.2, 7.5.2.3, 7.5.2.4, 7.5.2.5, 7.5.2.6 to 7.5.2.15, 7.6.2.1, 7.6.2.2, 7.7,8.3.5, 8.4.4, 8.5.2.2, 8.5.2.3, 8.5.2.5 to 8.5.2.17, 8.6.2.1, 8.6.2.2 and 8.7 )

TEST METHODS AND CRITERIA

A-1 TENSILE TESTS FOR STEEL ANDALUMINIUM LINERS

A tensile test shall be carried out on material takenfrom the cylindrical part of the finished liner using arectangular test piece shaped in accordance with themethod described in IS 15490 for steel and IS 15660for aluminum. The two faces of the test piecerepresenting the inside and outside surfaces of the linershall not be machined. The tensile test shall be carriedout in accordance with IS 1608.

The tensile strength shall meet the manufacturer’sdesign specifications. The elongation of steel liner shallbe at least 14 percent. The elongation of aluminiumalloy liners for hoop wrapped construction shall be atleast 12 percent. The elongation of aluminium alloyliners for full wrapped construction shall meet themanufacturer’s design specifications.

A-2 IMPACT TEST FOR STEEL LINERS

The impact test shall be carried out on material takenfrom the cylindrical part of the liner on three test piecesin accordance with IS 1757.

The impact test pieces shall be taken in the directionas required in Table 9 from the wall of the cylinder.The notch shall be perpendicular to the face of thecylinder wall. For longitudinal tests, the test piece shallbe machined all over (on six faces). If the wall thicknessdoes not permit a final test piece width of 10 mm, thewidth shall be as near as practicable to the nominalthickness of the cylinder wall. Test pieces taken in thetransverse direction shall be machined on four facesonly, the inner and outer face of the cylinder wall shallbe unmachined. The impact values shall be not lessthan those specified in Table 9.

24

IS 15935 : 2011

Table 9 Impact Test Acceptance Values(Clause A-2)

Cylinder Diameter D, mm >140 ≤140 Direction of Testing Transverse Longitudinal Width of Test Piece, mm 3-5 >5-7.5 >7.5-10 3-10 Test Temperature, °C -50 -50

Means of 3 specimens

30 35 40 60 Impact Strength, J/cm2 Individual

specimens 24 28 32 48

A-3 SULPHIDE STRESS CRACKING TEST FORSTEEL

If the upper limit of the specified tensile strength forthe steel exceeds 950 MPa, the steel from a finishedcylinder shall be subjected to a sulphide stress crackingresistance test.

The sulphide stress cracking resistance testing shallbe conducted in accordance with Annex B of IS 15490.Tests shall be conducted on a minimum of three tensilespecimens with a gauge diameter of 3.81mm machinedfrom the wall of a liner. The specimens shall be placedunder a constant tensile load equal to 60 percent ofthe specified minimum yield strength of the steel,immersed in a solution of distilled water buffered with0.5 percent (mass fraction) sodium acetate trihydrateand adjusted to an initial pH of 4.0 using acetic acid.The solution shall be continuously saturated at roomtemperature and pressure with 0.414 kPa hydrogensulphide (balance nitrogen). The tested specimensshall not fail within test duration of 144 h.

A-4 CORROSION TESTS FOR ALUMINIUM

Corrosion tests for aluminium alloy shall be carriedout in accordance with the procedure given in A-4.1and A-4.2 and meets the requirements given therein.

A-4.1 Tests for Assessing Susceptibility toIntercrystalline Corrosion

A-4.1.1 Principle

The method described below consists ofsimultaneously immersing the specimen taken fromthe finished cylinder liner under test in a corrosivesolution and examining them after a specified etchingtime in order to detect any signs of intercrystallinecorrosion and determine the nature and degree of suchcorrosion. The propagation of intercrystallinecorrosion is determined metallographically onpolished surfaces cut transversally to the etchedsurface.

A-4.1.2 Specimen Size

Specimens are taken from the head, body and base of

the cylinder (see Fig. 1). Each specimen shall be of thegeneral shape and the dimensions indicated in Fig. 2.

The faces a1-a2-a3-a4, b1-b2-b3-b4, a1-a2-b2-b1 anda4-a3-b3-b4 are all cut with a band saw and thencarefully trimmed with a fine file. The surfaces a1-a4-b4-b1 and a2-a3-b3-b2 which correspond respectivelyto the inner and outer faces of the cylinder liner areleft in their rough state.

A-4.1.3 Preparation of Specimen Surface BeforeCorrosive Etching

A-4.1.3.1 Reagents — Nitric acid, HNO3, analyticalgrade, density 1.33 g/cm3.

Hydroflouric acid, HF, analytical grade, density1.14 g/cm3 (at 40 percent) and Deionized or distilledwater

A-4.1.3.2 Prepare the following solution in a beaker:

HNO3 : 63 cm3

HF : 6 cm3

H2O : 931 cm3

a) Bring the solution to a temperature of 95oC.Treat each specimen, suspended on a wiremade of aluminium or another inert material,in this solution for 1 min.

b) Wash in running water and then in deionizedor distilled water.

c) Immerse the specimen in nitric acid for 1 minat room temperature to remove any copperdeposit, which may have formed.

d) Rinse in deionized or distilled water.e) To prevent oxidation of specimens they should

be plunged, as soon as they have beenprepared, into the corrosion bath intended forthem.

A-4.1.4 Preparation of Corrosive Solution

The corrosive solution to be used contains 57 g/l ofsodium chloride and 3 g/l of hydrogen peroxide.

A-4.1.4.1 Reagents

Sodium chloride, NaCl, crystallized, analyticalgrade;Hydrogen peroxide, H2O2, 100 to 110 volumes;Potassium permanganate, KMnO4; analyticalgrade;Sulphuric acid, H2SO4, analytical grade, density1,83 g/cm3;Deionized or distilled water; andTitration of hydrogen peroxide.

A-4.1.4.2 Since hydrogen peroxide is not very stable,it is essential to check its titre before use. To do this,

a) Take 10 cm3 of hydrogen peroxide using a

25

IS 15935 : 2011

FIG. 1 LOCATION OF SPECIMENS

FIG. 2 SPECIMEN SHAPE AND DIMENSIONS

Key1 — hole Ø 32 — thickness of the cylinder

All dimensions in millimetres.

26

IS 15935 : 2011

pipette and dilute to 1 000 cm3 (in a gaugedflask) with deionized or distilled water, thusobtaining a hydrogen peroxide solutionwhich will be called ‘C’. Using a pipette, placein a conical flask;

b) 10 cm3 of hydrogen peroxide solution C; andc) 2 cm3 approximately of sulphuric acid.

A solution of permanganate at 1.859 g/l is used for thetitration. The permanganate itself acts as an indicator.The reaction of the permanganate on the hydrogenperoxide in a sulfuric medium is expressed as:

2 KMnO4 + 5 H2O2 + 3 H2SO4 → K2SO4 + 2 MnSO4

+ 8 H2O + 5O2

Which gives the equivalence: 316 g KMnO4 = 170 gH2O2

Therefore 1 g of pure hydrogen peroxide reacts with1.859 g of potassium permanganate, hence the use ofa 1.859 g/l solution of potassium permanganate, whichsaturates volume, 1 g/l of hydrogen peroxide. Sincethe hydrogen peroxide was diluted 100 times to beginwith, the 10 cm3 of the test sample represents 0.1 cm3

of the original hydrogen peroxide.

Multiplying by ten the number of cubic centimetres ofpotassium permanganate solution used for titration, thetitre T of the original hydrogen peroxide in g/l is obtained.

Method for 10 litres Corrosive Solution Preparation:Dissolve 570 g of sodium chloride in deionized ordistilled water to obtain a total volume of about 9 litre.Add the quantity of hydrogen peroxide calculatedbelow. Mix and then make up the volume to 10 litreswith deionized or distilled water.

Calculate the volume of hydrogen peroxide to be putinto the solution as follows:

Quantity of hydrogen peroxide required 30 g.

If the hydrogen peroxide contains ‘T’ g of H2O2/litre,the volume required, expressed in cm3 will be

1 000 30¥T

A-4.1.5 Etching Conditions

The corrosive solution is placed in a crystallizer (orpossibly a large beaker), itself placed in a water bath.The water bath is stirred with a magnetic stirrer andthe temperature is regulated with a contactthermometer.

The specimen is either suspended in the corrosivesolution by a wire made of aluminium (or other inertmaterial) or placed in a solution so that it rests only onthe corners, the second method being preferable. The

etching time is 6 h and the temperature fixed at 30 ±1°C. Care shall be taken to ensure the quantity ofreagent is at least 10 cm3 per cm2 of specimen surface.

After etching, the specimen is washed in water,immersed for about 30 s in 50 percent dilute nitric acid,washed again in water and dried using compressed airfree of oil.

A number of specimens may be etched at the sametime provided that they are of the same type of alloyand that they are not in contact. The minimum quantityof reagent per unit of specimen surface area shall beadhered to.

A-4.1.6 Preparation of Specimens for Examination

Each specimen is placed vertically in a casting dish sothat it rests on face a1-a2-a3-a4. The casting dish can be ofexternal diameter 40 mm, height 27 mm, wall thickness2.5 mm. Around it is poured a mixture of epoxy resin andhardener (or equivalent) in the appropriate proportion.The usual setting time is about 24 hours.

A certain amount of material is removed from face a1-a2-a3-a4 preferably by lathe, so that the section a'1-a'2-a'3-a'4 when examined under the microscope, cannotshow corrosion from a1-a2-a3-a4. The distance betweenfaces a1-a2-a3-a4 and a'1-a'2-a'3-a'4 that is the thicknessremoved by the lathe, shall be at least 2 mm (see Fig. 2and Fig. 3).

KEY1 — casting mould2 — test piece3 — epoxy resin and hardner

FIG. 3 SPECIMEN IN CASTING DISH

Alternatively, prepare a section by sawing throughplane a'1-a'2-a'3-a'4 (see Fig. 2) to remove a specimenbetween 5 mm and 10 mm thick (that is such that thethickness from a'1 to a1 is between 5 mm and 10 mm).

27

IS 15935 : 2011

Mount this specimen in a thermosetting orthermoplastic mounting compound with face a'1-a'2-a'3-a'4 exposed to allow mechanical polishing.

The section for examination is polished mechanicallywith abrasive paper, a diamond compound and/ormagnesia polishing compound.

A-4.1.7 Micrographic Examination of Specimens

The examination is intended to assess the degree ofpenetration of intercrystallization corrosion into eachof the two faces, which make up the outer and innersurfaces of the cylinder.

The section is first examined at low magnification(for example X40) in order to locate the most corrodedareas, and then at a higher magnification, usuallyabout X 300, in order to assess the nature and extentof the corrosion.

A-4.1.8 Interpretation of Micrographic Examination

a) For alloys with an equiaxed crystal structurethe depth of corrosion shall not exceed thegreater of the following two values:1) Three grains in the direction

perpendicular to the face examined.2) 0.2 mm.

But in no case shall the depth exceed 0.3mm. However, it is permissible for these valuesto be exceeded locally provided that they arenot exceeded in more than four fields ofexamination at X 300 magnification.

b) For alloys with a crystal structure oriented inone direction through cold working, the depthof corrosion into each of the two faces, whichmake up the internal and external surfaces ofthe cylinder shall not exceed 0.1 mm.

A-4.2 Tests for Assessing Susceptibility to StressCorrosion

A-4.2.1 Principle

The method described below consists of the subjectionto stress of rings cut from the cylindrical part of thecylinder, their immersion in brine for a specified period,followed by removal of the brine and exposure to theair for a longer period and repetition of this cycle for30 days. If there are no cracks after the period of 30days, the alloy can be considered suitable for themanufacture of gas cylinders.

A-4.2.2 Tests Specimens

Six rings with a width of four times the actual wallthickness or 25 mm, whichever is the greater, are cutfrom the cylindrical part of the cylinder (see Fig. 4).The specimens shall have a 60° cut-out and besubjected to stress by means of a threaded bolt andtwo nuts (see Fig. 5).

Neither inner nor outer surfaces of the specimens shallbe machined.

A-4.2.3 Surface Preparation Before Corrosion Test

All traces of grease, oil and adhesive used with stressgauges shall be removed with a suitable solvent.

A-4.2.4 Preparation of Corrosive Solution

The brine is prepared by dissolving 3.5 parts ± 0.1parts (m/m) of sodium chloride in 96.5 parts (m/m) ofwater.

The pH of the freshly prepare solution shall be in therange 6.4 to 7.2.The pH may be corrected only by usingdilute hydrochloric acid or dilute sodium hydroxide.

The solution shall not be topped up by adding the saltsolution described, but only by adding distilled water


FIG. 4 SPECIMEN RING LOCATION

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up to the initial level in the vessel. Topping up maybe carried out daily if required. The solution shall becompletely replaced every week.

A-4.2.5 Applying Stress to Rings

Three of the rings shall be compressed so that the outersurface is under tension. The other three rings shall beexpanded so that the inner surface is under tension.

The rings shall be stressed to a maximum as givenby:

Re . F

where

Re = guaranteed minimum yield stress in MPa;and

F = design stress factor (variable).

The actual stress may be measured by electric stressgauges.

The diameter of the ring to achieve the required stressmay be calculated using the following equation:

2( )4

R D tD D

EtZπ −= −′

D' = diameter of the ring when compressed (orexpanded), in mm;

D = outside diameter of the cylinder, in mm;

t = cylinder wall thickness, in mm;

E = modulus of elasticity in MPa = 70 000 MPaapproximately;

Z = correction factor (see Fig. 6); and

R = (F . Re), in MPa.

It is essential for the nuts and bolts be electricallyinsulated from the rings and protected from corrosionby the solution. The six rings shall be completelyimmersed in the salt solution for 10 min. They are thenremoved from the solution and exposed to the air for50 min. This cycle shall be repeated for 30 days oruntil a ring break, whichever happens first. Thespecimens shall be visually inspected for any cracks.

A-4.2.6 Interpretation of Results

The alloys shall be considered acceptable for themanufacture of gas cylinder if none of the ringssubjected to stress develops any cracks visible to thenaked eye or visible at low-magnification (X 10 toX 30), at the end of the 30 day test period.

A-4.2.7 Possible Metallographic Examination

In the event of doubt about the presence of cracks (forexample line of pitting), uncertainty may be removedby means of an additional metallographic examinationof a section taken perpendicular to the axis of the ringsin the suspect area. A comparison is made of the form(inter-or trans-crystalline) and depth of penetration the

FIG. 5 STRESSED SPECIMENS

Key1 — threaded bar2 — insulating bush3 — nut

5A Stressed Internally 5B Stressed Externally

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corrosion on the faces of the ring subjected to tensileand compressive stress.

The alloys shall be considered accepted if the corrosionon each face of the ring is similar. If, however, the faceof the ring under tension reveals inter-crystalline crackswhich are clearly deeper than those in the face undercompression, the ring shall be considered to have failedthe test.

A-5 SUSTAINED LOAD CRACKING (SLC)TESTS FOR ALUMINIUM

A-5.1 Principle

A fatigue precracked specimen is loaded by a constantload or constant displacement method to stress intensityKIAPP equal to a defined value. The specimen is kept inthe loaded condition for a specified time andtemperature. After the test period, the specimen isexamined to assess whether the initial fatigue crackdid or did not grow.

KIAPP = applied elastic stress-intensity, in MPa ;m

V = crack-mouth opening displacement(CMOD), in mm, defined as the mode 1(also called opening mode) component ofcrack displacement due to elastic and plasticdeformation, measured at the location on acrack surface that has the greatest elasticdisplacement per unit load;

ReSLC = average of measured yield stress of twospecimens from the test cylinder

representing the SLC test specimenslocation at room temperature, in MPa;

r = notch radius;

Kt = theoretical elastic stress concentrationfactor;

Kt’ = apparent crack tip stress intensity factorcalculated on the basis of the notch depthand applied load;

M = bending moment;

µ = Poisson’s ratio;

SLC = Sustained load cracking; and

KISCC = threshold stress intensity factor forsusceptibility to stress corrosion cracking.

Liners with nominal neck and shoulder wall thickness≤ 7 mm are exempt from the sustained load crackingtests. The inspector shall ensure that the neck/shoulderwall thickness of the actual cylinders reasonablyrepresents the quoted nominal figure. Figure 7illustrates the neck and shoulder thickness.

A-5.2 Specimen Configurations and Number of Tests

A-5.2.1 Any one or a combination of specimengeometries of the following listed specimens shall beused for the tests:

a) Compact tension test (CTS) specimen, seeFig. 8;

b) Double cantilever beam (DCB) specimen, seeFig. 9;

FIG. 6 CORRECTION FACTOR Z PLOTTED AGAINST D/a

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IS 15935 : 2011

c) T-type wedge opening loaded (T-WOL)specimen, see Fig. 10; and

d) C shaped specimen, see Fig. 11.

A-5.2.2 Specimen orientation shall be Y-X or Y-Z asshown in Fig. 12.

A-5.2.3 At least three specimens from the cylinder walland if possible three specimens from the shoulder andthree from the neck shall be tested. At each location,three specimens shall be taken as close to each otheras possible. One specimen from each location shall beused for SLC testing and two from each location fortensile testing.

Key1 — normal neck thickness2 — nominal shoulder thickness

NOTE — a-b, c-d, e-f and g-h are tangents initiating atintersecting surfaces.

FIG. 7 ILLUSTRATION OF NECK AND SHOULDER THICKNESS

A-5.2.4 Flattening of specimen blanks is not allowed.

A-5.2.5 If test specimen thickness cannot be obtainedfrom the specified location or locations to meet thevalidity requirements given below, then the thickestpossible specimen shall be tested. The specimen shallbe taken when the mechanical properties have beenfully developed in the cylinder but before any externalmachining of the neck/shoulder area. Validityrequirement for the specimen is given as:

2

IAPPn

eSLC

, , , ( ) 1.27 1 000 Ê ˆ

- ≥ ¥Á ˜Ë ¯K

a B B W aR

The notations are as indicated in the specimen sketchesgiven Fig. 8 to Fig. 11. Bn refers the reduced thicknessat side groove (minimum side-side dimension betweenthe notches in side grooved specimens).

A-5.2.6 When it is impossible to obtain full size tensilespecimens, small size specimens are permitted fordetermination of yield stress.

A-5.3 Fatigue Pre-cracking

A-5.3.1 The machine used for fatigue cracking shallhave a means of loading such that the stress distributionis symmetrical about the notch and the applied loadshall be known to an accuracy of ± 2.5 percent.

A-5.3.2 The environmental conditions apparent duringfatigue pre-cracking, as well as the stressing conditions,can influence the subsequent behaviour of the specimenduring stress corrosion testing. In some materials, theintroduction of the stress corrosion test environmentduring the pre-cracking operation will promote achange from the normal ductile transgranular mode offatigue cracking to one that more closely resemblesstress corrosion cracking. This may facilitate thesubsequent initiation of stress corrosion cracking andlead to the determination of conservation initiationvalues of KISCC. However, unless facilities are availableto commence stress corrosion testing immediatelyfollowing the pre-cracking operation, corrodentremaining at the crack top may promote blunting dueto corrosive attack. Furthermore, the reproducibilityof results may suffer when pre-cracking is conductedin the presence of an aggressive environment becauseof the greater sensitivity of the corrosion fatiguefracture mode to the cyclic loading conditions. Inaddition, more elaborate facilities may be needed forenvironmental control purposes during pre-cracking.For these reasons, it is recommended that, unless agreedotherwise between the parties, fatigue pre-crackingshall be conducted in the normal laboratory airenvironment.

A-5.3.3 The specimens shall be pre-cracked by fatigueloading with an R value in the range 0 to 0.1 until thecrack extends at least 2.5 percent W or 1.25 mm beyondthe notch at the side surfaces, whichever is greater.

A-5.3.4 The final length of the fatigue crack shall besuch that the requirement for plane strain predominanceis satisfied by the following equation:

2

IAPP

eSLC

1.27 1 000K

aR

> ×

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IS 15935 : 2011


FIG. 8 PROPORTIONAL DIMENSIONS AND TOLERANCES FOR COMPACT TENSILE TEST PIECE

Net width = WTotal width, C = 1.25 W, MinThickness, B = 0.5 WHalf height, H = 0.6 WHole diameter, D = 0.25 WHalf distance between = 1.6 DHole outer Edges, FNotch width, N = 0.065 W, MaxEffective notch, length, ! = 0.25 W to 0.40 WEffective crack, length, a = 0.45 W to 0.55 W

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FIG. 9 PROPORTIONAL DIMENSIONS AND TOLERANCES FOR DOUBLE CANTILEVER BEAM TEST PIECE

Half height = HThickness, B = 2 HNet width, W = 10 H, MinTotal width, C = W + dScrew diameter, d = 0.75 H, MinNotch width, N = 0.14 H, MaxEffective notch, length, ! = 2 H

NOTES1 “A” surfaces should be perpendicular and parallel as applicable to within 0.002 H TIR.2 At each side point “B” should be equidistant from the top to bottom surface to within 0,001 H.3 The bolt centreline should be normal to the specimen centreline to within 1°.4 The bolt material should be similar to that of the specimen, fine threaded with a square or allen-screw head.5 Surface roughness values in microns.

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FIG. 10 PROPORTIONAL DIMENSIONS AND TOLERANCE FOR MODIFIED WEDGE OPENING LOADED TEST PIECES

NOTES1 Surfaces should be perpendicular and parallel as applicable to within 0.002 H TIR.2 The bolt centreline should be normal to the specimen centreline to within 1°.3 The bolt material should be similar to that of the specimen, fine threaded with a square or allen-screw head.4 Surface roughness values in microns.

Thickness = BNet width, W = 2.55 BTotal width, C = 3.20 + BHalf height, H = 1.24 BHole diameter, D = 0.718 B ± 0.003 BEffective notch, length, ! = 0.77 BNotch width, N = 0.06 BThread diameter, T = 0.625 BDistance from hole = 0.239 BCentreline to notchCentreline, F

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FIG. 11 PROPORTIONAL DIMENSIONS AND TOLERANCES FOR C SHAPED TEST PIECES

NOTES1 All surfaces should be perpendicular and parallel as applicable to within 0.002 W TIR and “E” surface should beperpendicular to “Y” surfaces to within 0.02 W TIR.2 Surface roughness values in microns.

Net width = WThickness, B = 0.5 W ± 0.01 WDistance from hole axes to = 0.50 W ± 0.005 WTangent with the inner surface, XNotch width, N = 1.5 Min (0.1 W, Max)Notch length, ! = 0.3 WDistance from the hole = 0.25 W ± 0.01 WAxes to face of the specimen, ZDistance from the hole axes to outer surface, T = 0.25 W ± 0.01 WDiameter of holes, D = 0.25 W ± 0.005 W

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NOTES1 Specimen should be taken as close as possible to neck.2 Notch direction shall be toward the neck, as shown.

FIG. 12 ORIENTATION OF NECK, SHOULDER AND

CYLINDER WALL SPECIMEN

A-5.4 Specimen Testing Procedure

A-5.4.1 Before testing, the thickness B and either widthW or half-height H [in the case of (W–a) in differentspecimens] shall be measured to within 0.1 percent W(or H) from the crack plane.

A-5.4.2 Load the fatigue pre-cracked specimens to astress-intensity KIAPP determined from the followingequation:

KIAPP = 0.056 ReSLC

Specimens shall be loaded by a suitable constantdisplacement or constant load method.

A-5.4.3 For specimens loaded by a constantdisplacement method, the loading shall be either thenon-monitored load method or the monitored loadmethod and shall meet the following requirements.

a) For non-monitored load method:1) Record the crack mouth opening

displacement (CMOD) at the end of thetest, before unloading;

2) Unload the specimen; and3) Reload the specimen up to the measured

CMOD in a device suitable for loadmeasurement, Record the load and usethis load in the KIAPP calculations. Thiscalculated KIAPP shall be equal to orgreater than the calculated KIAPP valuefrom A-5.4.2.

b) For monitored load method:1) The final load at the end of the test period

shall be applied in the KIAPP calculations;2) This calculated KIAPP shall be equal to or

greater than the calculated KIAPP valuefrom A-5.4.2.

A-5.4.4 Testing Using the Constant DisplacementMethod

a) For testing of compact tension specimen(CTS) specimens at a constant displacementloading, use the following equations todetermine V:

IAPP

N

( )

(0.032)( )( ( ))( / )

K WV

E f x B B=

2

2

2.24(1.72 0.9 )( 1 )( )

(9.85 0.17 11 )

x x xf x

x x

− + −=− +

x = a/W.

b) For testing of C-shaped specimens at aconstant displacement loading, use thefollowing equations:For specimens with X/W = 0

V = IAPP 1 1 2 1( )( )( )[0.43(1 / ) ](0.032)( )( )

K W P r r QE Y

− +

For specimens with X/W = 0.5

V = IAPP 2 1 2 2( )( )( )[0.45(1 / ) ](0.032)( )( )

K W P r r QE Y

− +

where

Y =3 5

18.23 106.2 397.7Ê

- +ÁË

a a aW W W

7 9

582.0 369.1ˆ

- - ¥˜¯

a aW W 1 1.54

Ê +ÁËXW

1

2

0.5 1 0,22 1 1È ˘Ê ˆ Ê ˆˆ+ ¥ + - -Í ˙˜ Á ˜ Á ˜¯ Ë ¯Ë ¯Í ˙Î ˚

ra aW W r

P1 = (1 + a/W)/(1– a/W)2 ;

Q1 = 0.542 + 13.137 (a/W) – 12.316 (a/W)2

+ 6.576 (a/W)3

Key1 — Neck specimen Y - Z2 — Neck specimen Y - X3 — Shoulder specimeny Y - Z4 — Cylinder wall specimeny Y - X

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IS 15935 : 2011

P2 = (2 + a/W) / (1– a/W)2;

Q2 = 0.399 + 12.63 (a/W) – 9.838 (a/W)2 +4.66 (a/W)3

c) The stress intensity factor equations for DCBand T-WOL specimens are:

The stress intensity factor equations fordouble cantilever beam specimen (DCB)

2 3yLL

1 3 2

3 ( 0.6 )

4 ( 0.6 )

¥ + +=

È ˘+ +Î ˚

E V H H a H HK

a H H a

The stress intensity factor equations for wedge openingloaded specimen (WOL)

1

YPK

B a=

where2 3

4 5

30.96 195.8 730.6

1186.3 754.6

Ê ˆ Ê ˆ Ê ˆ= - + +Á ˜ Á ˜ Á ˜Ë ¯ Ë ¯ Ë ¯Ê ˆ Ê ˆ+Á ˜ Á ˜Ë ¯ Ë ¯

a a aY

W W Wa aW W

A-5.4.5 Testing Using the Constant Loading Method

a) For testing DCB specimens at a constant load(P), the following equation shall be used:

IAPP 3/2

2.383.46

Pa HK

aBH = +

The above equation shall satisfy thefollowing validity requirements.

2 ≤ a/H ≤ 10

W/a + 2H

b) For testing of CTS, T-WOL and C shapedspecimens at a constant load, the stressintensity factor equations given in theprevious section (see 5.4.4) shall be used.

A-5.4.6 The loaded specimens shall be tested for90 days at room temperature.

A.5.4.7 If the additional test referred to in A-5.5.4 isrequired then repeat the entire procedure using onlyconstant load conditions for a period of 180 days atroom temperature.

A-5.5 Crack Growth Examination

A-5.5.1 After the specified test period, unload thespecimen, fatigue the specimen at maximum stressintensity not exceeding 0.6 KIAPP till the crack

advances by at least one millimeter. After fatiguecracking, break open the specimen.

A-5.5.2 Measure the distance between the two pre-and post-fatigue cracks using a scanning electronmicroscope (SEM). Measurements shall be takenperpendicular to the pre- and post-fatigue cracks at25 percent B, 50 percent B and 75 percent B locations.Calculate the average of these three values.

A-5.5.3 If the average measured distance between thetwo fatigues cracks does not exceed 0.16 mm, thespecimen passes the test. If all the specimens pass, thealloy is qualified.

A-5.5.4 If the average measured values exceed0.16 mm, the alloy may be qualified if, when subjectedto the test described in A-5.4.8, the average measureddistance between the two fatigue cracks does notexceed 0.3 mm. A-5.5.1 and A-5.5.2 shall also apply.

A-5.6 Interpretation of Results

If the test specimen exhibits less than or equal to aspecified amount of crack growth, then the material ischaracterized as suitable for gas cylinders with respectto the sustained-load-cracking resistance requirement.

Following the initial qualification for resistance tosustained-load-cracking, this procedure shall only berepeated, if it applies any one of the followingconditions:

a) It is manufactured in a different factory;b) It is manufactured by a different process such

as,1) Cold or hot extrusion, from cast or

extruded or rolled billet;2) Cold or hot extrusion followed by cold

drawing from cast or extruded or rolledbillet;

3) Cupping, flow forming, spinning andcold drawing sheet or plate; and

4) Open necking at both ends of an extrudedor cold drawn tube.

c) It is manufactured from an alloy of differentcomposition limits from that used in theoriginal prototype tests; and

d) It is given a different heat treatment that isoutside the temperature range of 20°C and/or for times shorter than those used for theoriginal type approval less 10 percent.

A-5.7 Cylinder Thickness Qualification

If the specimen validity requirements are not met, thenthe material is suitable upto a maximum thickness ofthe cylinder location from where the specimens weretaken provided the specimens meet the other

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IS 15935 : 2011

requirements of this test method. The material issuitable for all thicknesses if the specimens meet thevalidity requirements and the other requirements ofthis test method.

A-6 LEAK-BEFORE-BREAK (LBB) TEST

Three finished cylinders shall be pressure cycledbetween 20 bar and 300 bar at a rate not to exceed 10cycles per minute in accordance with A-12. Allcylinders shall either fail by leakage or exceed 45 000pressure cycles.

A-7 EXTREME TEMPERATURE PRESSURECYCLING

Finished cylinders, with the composite wrapping free ofany protective coating, shall be cycle tested, as follows:

a) Condition for 48 h at zero pressure, 65°C orhigher and 95 percent or greater relativehumidity. The intent of this requirement shallbe deemed met by spraying with a fine sprayor mist of water in a chamber held at 65°C;

b) Hydrostatically pressurize for 500 cyclesmultiplied by the specified service life in yearbetween 20 bar and 260 bar at 65°C or higher,and 95 percent or greater relative humidity;

c) Condition the cylinder and fluid at –40°C orlower as measured in the fluid and on thecylinder surface; and

d) Pressurize from 20 bar to 200 bar for 500 cyclesmultiplied by the specified service life in yearsat –40°C or lower. Adequate recordinginstrumentation shall be provided to ensure theminimum temperature of the fluid ismaintained during the low temperature cycling.

The pressure cycling rate of (b) shall not exceed10 cycles per minute. The pressure cycling rate of (d)shall not exceed 3 cycles per minute unless a pressuretransducer is installed directly within the cylinder.

During this pressure cycling, the cylinder shall showno evidence of rupture, leakage or fibre unravelling.

Following pressure cycling at extreme temperatures,cylinder shall be hydrostatically pressured to failurein accordance with A-11, and achieve a minimum burstpressure of 85 percent of the minimum design burstpressure. For non-metal lined full wrapped designs,prior to the hydrostatic burst test, the cylinder shall beleak tested in accordance with A-9.

A-8 BRINELL HARDNESS TEST

Hardness test shall be carried out on the parallel wallof each liner in accordance with IS 1500 at the rate ofone test per metre length of parallel wall. The test shallbe carried out after the final heat treatment and the

hardness values thus determined shall be in the rangespecified for the design.

A-9 LEAK TEST FOR NON-METAL-LINEDFULL WRAPPED CYLINDERS

Non-metal-lined full wrapped designs shall be leaktested using the following procedure (or an alternativeacceptable to the inspector):

a) Thoroughly dry the cylinders;b) Pressurize the cylinders to working pressure

with dry air or nitrogen containing adetectable gas such as helium.

Any leakage detected shall be cause for rejection.

NOTE — Leakage is the release of gas through a crack, pore,unbond or similar defect.Permeation through the wall in compliance with A-20 is notconsidered to be leakage.

A-10 HYDRAULIC TEST

Any internal pressure applied after auto-frettage andprior to the hydrostatic test shall not exceed 90 percentof the hydrostatic test pressure.

One of the following two options shall be used.

A-10.1 Volumetric Expansion Test

a) The cylinder shall be hydrostatically testedto at least 1.5 times working pressure. In nocase shall the test pressure exceed theauto-frettage pressure.

b) Pressure shall be maintained for 30s andsufficiently longer to ensure completeexpansion. Any internal pressure applied afterauto-frettage and prior to the hydrostatic testshall not exceed 90 percent of the hydrostatictest pressure. If the test pressure cannot bemaintained due to failure of the test apparatus,it is permissible to repeat the test at a pressureincreased by 7 bar. No more than 2 such repeattests are permitted.

c) Any cylinders not meeting the definedrejection limit shall be rejected and renderedunserviceable.

A-10.2 Proof Pressure Test

The hydrostatic pressure in the cylinder shall beincreased gradually and regularly until the testpressure, at least 1.5 times working pressure is reached.The cylinder test pressure shall be maintained for atleast 30s to establish that there are no leaks.

A-11 HYDROSTATIC PRESSURE BURST TEST

The rate of pressurization shall not exceed 14 bar/s atpressures in excess of 80 percent of the design burst

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IS 15935 : 2011

pressure. The rate of pressurization at pressures inexcess of 80 percent of the design burst pressureexceeds 3.5 bar/s, then either the cylinder shall beplaced schematically between the pressure source andthe pressure measurement device, or there shall be a5s hold at the minimum design burst pressure.

The minimum required (calculated) burst pressure shallbe at least 450 bar, and in no case less than the valuenecessary to meet the stress ratio requirements. Actualburst pressure shall be recorded. Rupture may occur ineither the cylindrical region or the dome region of thecylinder.

A-12 AMBIENT TEMPERATURE PRESSURECYCLING

Pressure cycling shall be performed in accordance withthe following procedure:

a) Fill the cylinder to be tested with a non-corrosive fluid such as oil, inhibited water orglycol; and

b) Cycle the pressure in the cylinder between20 bar and 260 bar at a rate not exceeding10 cycles per minute.

The number of cycles to failure shall be reported, alongwith the location and description of the failureinitiation.

A-13 ACID ENVIRONMENT TEST

On a finished cylinder the following test procedureshall be applied:

a) Expose a 150 mm diameter area on thecylinder surface for 100 h to a 30 percentsulphuric acid solution (battery acid with aspecific gravity of 1.219) whilst the cylinderis hydrostatically pressurized to 260 bar; and

b) Pressurize the cylinder to burst in accordancewith the procedure defined in A-11.

The burst pressure shall exceed 85 percent of theminimum design burst pressure.

A-14 BONFIRE TEST

A-14.1 General

The bonfire test is designed to demonstrate that finishedcylinders, complete with the fire protection system(cylinder valve, pressure relief devices and/or integralthermal insulation) specified in the design, will preventthe rupture of the cylinder when tested under the specifiedfire conditions. Precautions shall be taken during firetesting in the event that cylinder rupture occurs.

A-14.2 Cylinder Set-up

The cylinder shall be placed horizontally with the

cylinder bottom approximately 100 mm above the firesource.

Metallic shielding shall be used to prevent direct flameimpingement on cylinder valves, fittings, and/orpressure relief devices. The metallic shielding shall notbe in direct contact with the specified fire protectionsystem (pressure relief device or cylinder valve).

Any failure during the test of a valve, fitting or tubingthat is not part of the intended protection system forthe design shall invalidate the result.

A-14.3 Fire Source

A uniform fire source of 1.65 m length shall providedirect flame impingement on the cylinder surfaceacross its entire diameter.

Any fuel may be used for the fire source provided itsupplies uniform heat sufficient to maintain thespecified test temperatures until the cylinder is vented.The selection of a fuel should take into considerationair pollution concerns. The arrangement of the fireshall be recorded in sufficient detail to ensure that therate of heat input to the cylinder is reproducible.

Any failure or inconsistency of the fire source duringa test shall invalidate the result.

A-14.4 Temperature and Pressure Measurements

Surface temperature shall be monitored by the leastthree thermocouples located along the bottom of thecylinder and spaced not more than 0.75 m apart.

Metallic shielding shall be used to prevent direct flameimpingement on the thermocouples. Alternatively,thermocouples may be inserted into blocks of metalmeasuring less than 25mm2.

Thermocouple temperature and the cylinder pressureshall be recorded at intervals of every 30 s or less duringthe test.

A-14.5 General Test Requirements

The cylinder shall be pressurized to working pressurewith natural gas or compressed air and tested in thehorizontal position at working pressure and at25 percent of working pressure if a thermally activatedPRD is not used.

Immediately following ignition, the fire shall produceflame impingement on the surface of the cylinder alongthe 1.65 m length of the fire source and across thecylinder diameter.

Within 5 min of ignition, the temperature in at leastone thermocouple shall indicate a temperature ≥590°C. This minimum temperature shall be maintainedfor the remainder of the test.

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IS 15935 : 2011

For cylinders of length 1.65 m or less, the centre of thecylinder shall be positioned over the centre of the firesource.

For cylinders of length greater than 1.65 m, thecylinder shall be positioned as follows:

a) If the cylinder is fitted with a pressure reliefdevice at one end, the fire source shallcommence at the opposite end of the cylinder;

b) If the cylinder is fitted with a pressure reliefdevice at both ends, or at more than onelocation along the length of the cylinder, thecentre of the fire source shall be centeredmidway between the pressure relief devicesthat are separated by the greatest horizontaldistance; and

c) If the cylinder is additionally protected usingthermal insulation, then two fire tests atservice pressure shall be performed, one withthe fire centered midway along the cylinderlength, and the other the fire commencing atone of the ends of a second cylinder.

A-14.6 Acceptable Results

The cylinder shall vent through a pressure reliefdevice.

A-15 PENETRATION TESTS

A cylinder pressurized to 200 ± 10 bar with compressedgas shall be penetrated by an armour piercing bulletwith a diameter of 7.62 mm or greater. The bullet shallcompletely penetrate at least one side wall of thecylinder. The projectile shall impact the sidewall atan approximate angle of 45°. The cylinder shall notrupture.

A-16 COMPOSITE FLAW TOLERANCE TESTS

One finished cylinder, complete with protectivecoating, shall have flaws cut into the composite inthe longitudinal direction. The flaws shall be greaterthan visual inspection limits as specified by themanufacturer. As a minimum, one flaw shall be25 mm long and 1.25 mm in depth and another flawshall be 200 mm long and 0.75 mm in depth, cut inthe longitudinal direction into the cylindersidewall.

The flawed cylinder shall then be pressure cycledbetween 20 bar and 260 bar at ambient temperature,initially for 3 000 cycles, then followed by anadditional 12 000 cycles.

The cylinder shall not leak or rupture within the first3 000 cycles, but may fail by leakage during the further12 000 cycles. All cylinders which complete this testshall be destroyed.

A-17 HIGH TEMPERATURE CREEP TEST

This test is required for designs in which the glasstransition temperature of the resin matrix does not exceed102°C. One finished cylinder shall be tested as follows:

a) The cylinder shall be pressurized to 260 barand held at a temperature of 100°C for notless than 200 h; and

b) Following the test, the cylinder shall meet therequirements of the hydrostatic expansion test(see A-10), the leak test (see A-9) and thehydrostatic pressure burst test (see A-11).

A-18 ACCELERATED STRESS RUPTURETEST

One cylinder shall be hydrostatically pressurized to 260bar at 65°C. The cylinder shall be held at this pressureand temperature for 1 000 h. The cylinder shall thenbe pressured to burst in accordance with the proceduredescribed in A-12, except that the burst pressure shallexceed 85 percent of the minimum design burstpressure.

A-19 IMPACT DAMAGE TEST (DROP TEST)

One or more finished cylinders shall be drop tested atambient temperature without internal pressurization orattached valves. The surface on to which the cylindersare dropped shall be a smooth, horizontal concrete pador flooring. One cylinder shall be dropped in ahorizontal position with the bottom 1.8 m above thesurface on to which it is dropped. One cylinder shallbe dropped vertically on each end at a sufficient heightabove the floor or pad so that the potential energy is488 J, but in on case shall the height of the lower endbe greater than 1.8 m. One cylinder shall be droppedat a 45° angle on to a dome, from a height such thatthe center of gravity is at 1.8 m; however, if the lowerend is closer to the ground than 0.6 m, the drop angleshall be changed to maintain a minimum height of0.6 m and a center of gravity of 1.8 m.

Following the drop impact, the cylinders shall then bepressure cycled between 20 bar and 260 bar at ambienttemperature, initially for 3 000 cycles, then followedby an additional 12 000 cycles.

The cylinder shall not leak or rupture within the first3 000 cycles, but may fail by leakage during the further12 000 cycles. All cylinders which complete this testshall be destroyed.

A-20 PERMEATION TEST

This test is required only for non-metal lined fullwrapped cylinders. One finished cylinder shall be filledwith compressed nature gas to working pressure, placedin an enclosed sealed chamber at ambient temperature,

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and monitored for leakage for 500 h. The permeationrate shall be less than 0.25 ml of natural gas per hourper litre water capacity of the cylinder. The cylindershall be sectioned and the internal surfaces inspectedfor any evidence of cracking or deterioration.

A-21 TENSILE PROPERTIES OF PLASTICS

The tensile yield strength and ultimate elongationof plastic liner material shall be determined at –50°C. For the determination of tensile properties ofplastics, the general testing principles given inSection 1 and 2 of IS 13360 (Part 5) may be referred.The test results shall demonstrate the ductileproperties of the plastic l iner material attemperatures of –50°C or lower by meeting thevalues specified by the manufacturer.

A-22 SOFTENING TEMPERATURE OFPLASTICS

Polymeric materials from finished liners shall be testedin accordance with a method described in IS 13360(Part 6)/Sec 1. The softening temperature shall be atleast 100°C.

A-23 BOSS TORQUE TEST

The body of the cylinder shall be restrained againstrotation and a torque of twice the valve or PRDinstallation torque specified by the manufacturer shallbe applied to each end boss of the cylinder. The torqueshall be applied first in the direction of tightening athreaded connection, then in the enlighteningdirection and finally again in the tightening direction.The cylinder shall then be subjected to a leak test inaccordance with A-9.

A-24 RESIN SHEAR STRENGTH

Resin material shall be tested on a sample couponrepresentative of the composite overwrap inaccordance with the procedure given in this clause.Following 24 h boiling in water the composite shallhave minimum shear strength of 13.8 MPa.

A-24.1 Principle

A bar of rectangular cross-section is loaded as a simplebeam in flexure so that interlaminar shear failureoccurs. The bar rests on two supports and the load isapplied by means of a loading member midwaybetween the supports.

The result obtained is not an absolute value. For thisreason the term ‘apparent inter-laminar shear strength’is used to define the quantity measured. Test resultsfrom different-sized specimens, or from specimenstested under different conditions, are not directlycomparable.

A-24.2 Test Specimens

A-24.2.1 Standard Test Specimens

Test specimens shall comprise rectangular bars ofuniform thickness:

Thickness (h) : 2 ± 0.2 mmOverall length (l) : 20 ± 1 mmWidth (b) : 10 ± 0.2 mm

A-24.2.2 Other Test Specimens

When it is not desirable to use the standard specimen,the following rules shall be observed:

a) The length and the thickness of the testspecimen shall be in the same ratio as in thestandard specimen, that is, length (l) = 10 h.

b) The width shall be chosen in the same ratioto the thickness as in the standard specimen,that is, width (b) = 5 h.

Depending upon the material being tested, specimensof 2 mm thickness may fail by shear or experiencecompression failure under load or exhibit extremedeflection without shear failure. As specimen thickness(height) is increased, the probability of compressionfailure under the load increases and the probability ofextreme deflection with no failure decrease. Asspecimen thickness is decreased, the reverse is true. Itis important to select a specimen thickness that willcause specimens to fail by horizontal shear.

A-24.3 Test Set-up

The width of the loading member and the supports shallbe greater than the test specimen width (see Fig.13).The loading member shall apply the load mid-waybetween the supports. The span (distance between thesupports) shall be adjustable. The load indicator shallbe such that the error in the indicated loads is less than61 percent of full scale. The radius of the loadingmember r1 shall be 5 ± 0.2 mm and that of the supportsr2 shall be 2 ± 0.2 mm.

NOTE — Measure at the mid-point of each test specimen,the width b and the thickness h of the specimen to thenearest 0.02 mm using a micrometer or an equivalent.

A-24.4 Preparation of Specimens

Machine the test specimens from a moulded blank orsheet. The specimens shall be flat and free of twist.The surfaces and edges shall be free from defects. Thethickness along the whole length shall be within ± 5percent of the mean thickness. The width of individualspecimens shall be constant to within 0.2 mm.

Specimens showing measurable or observabledeparture from one or more of these requirements shallbe rejected or machined to the required size and shape

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before testing.

A-24.5 Number of Test Specimens

At least five test specimens shall be tested.

When the fiber orientation and distribution in thematerial to be tested does not differ significantlybetween the two principal directions, shear specimensshall be taken in each of these two directions. Whenthe material has a preferred orientation, the specimens

shall be taken in this direction (see Fig. 14).

A-24.6 Procedure

Set the span L to 5 h ± 0.3 mm, where h is the meanthickness of the set of specimens. For some materials,a shorter span may be necessary to produceinter-laminar shear failure. Place the test specimensymmetrically across the two parallel supports withan unmachined surface in contact with the supports.

FIG. 14 LOCATIONS OF SPECIMEN

FIG. 13 LOADING CONFIGURATION

r1

r2r2

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Apply the force uniformly across the width of the testpiece by means of the loading member, parallel to andmidway between the supports. Record the forcethroughout the test.

A-24.7 Mode of Failure

Record the mode of failure using the followingclassification.

A-24.7.1 Acceptable inter-laminar shear failure mode:

a) Single shear, multiple shear [see Fig. 15A]:Unacceptable failure modes;

b) Mixed modes of failure [see Fig. 15B]: Shearand tension, shear and compression;

c) Non-shear modes of failure [see Fig. 15C]:tension, compression; and

d) Plastic shear [see Fig. 15D].

NOTE —There are two possible failure cases:a) For failure by mode “a”, approximately in the plane

of the neutral axis, the apparent inter-laminar shearstrength can be calculated as shown in A-24.8.

b) For failure by mode “b” and “c”, the resultcalculated in accordance with A-24.8 is not inter-laminar shear strength and may only be used tocompare test specimens taken from the samematerial.

A-24.8 Calculation and Expression of Result

Calculate the apparent interlaminar shear strength tm,expressed in MPa:

mm

34

t = Fbh

where

Fm = failure (or) maximum load, in N;

b = width of the test specimen, in mm; and

h = thickness of the test specimen, in mm.

A-25 NATURAL GAS CYCLING TEST FOR NON-METAL-LINED FULL WRAPPED CYLINDER

Special consideration shall be given to safety whenconducting this test. Prior to conducting this test,cylinders of this design shall have successfully passedthe test requirements of A-9, A-11, A-12 and A-20.

One finished cylinder of non-metal lined full wrappedconstruction shall be pressure cycled using compressednatural gas between less than 20 bar and workingpressure for 1 000 cycles. The filling time shall be5 min maximum. Unless otherwise specified by themanufacturer, care should be taken to ensure thattemperatures during venting do not exceed the definedservice conditions.

The cylinder shall be leak tested in accordancewith A-9 and meet the requirements therein. Followingthe completion of the natural gas cycling, the cylindershall be sectioned and liner/end boss interface inspectedfor evidence of any deterioration, such as fatiguecracking or electrostatic discharge.

15A Shear Modes of Failure — Acceptable Inter-Laminar Shear Failure

15B Non-Shear Modes of Failure — Unacceptable Inter-Laminar Shear Failure

FIG. 15 MODES OF FAILURE — Continued

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FIG. 15 MODES OF FAILURE

15C Non-Shear Modes of Failure — Unacceptable Inter-Laminar Shear Failure

15D Plastic Chear — Unacceptable Inter-Laminar Shear Failure

ANNEX B(Clauses 5.1, 6.7 and 7.7)

ULTRASONIC INSPECTION

B-1 GENERAL

This Annex is based on techniques used by cylindermanufacturers. Other techniques of ultrasonic inspectionmay be used, provided these have been demonstrated tobe suitable for the manufacturing method.

B-2 GENERAL REQUIREMENTS

The outer and inner surfaces of any cylinder which isto be tested ultrasonically shall be in a conditionsuitable for an accurate and reproducible test.

For flaw detection, the pulse echo system shall be used.For thickness measurement either the resonance methodor the pulse echo system shall be used. Either contact orimmersion techniques of testing shall be used.

A coupling method which ensures adequatetransmission of ultrasonic energy between the testingprobe and the cylinder shall be used.

B-3 FLAW DETECTION OF THECYLINDRICAL PARTS

B-3.1 Procedure

The cylinders to be inspected and the search unit shallhave a rotating motion and translation relative to oneanother such that a helical scan of the cylinder isdescribed. The velocity of rotation and translation shall

be constant within ±10 percent. The pitch of the helixshall be less than the width covered by the probe (atleast a 10 percent overlap shall be guaranteed) and berelated to the effective beam width such as to ensure100 percent coverage at the velocity of rotation andtranslation used during the calibration procedure.

An alternative scanning method may be used fortransverse defect detection, in which the scanning orrelative movement of the probes and the work piece islongitudinal, the sweeping motion being such as toensure a 100 percent surface coverage with about 10percent overlap of the sweeps.

The cylinder wall shall be tested for longitudinaldefects with the ultrasonic energy transmitted in bothcircumferential directions and for transverse defectsin both longitudinal directions.

In this case or when optional testing is carried out onthe transition areas between the wall and neck and/orwall and base, this may be conducted manually if notcarried out automatically.

The effectiveness of the equipment shall be periodicallychecked by passing a reference standard through thetest procedure. This check shall be carried out at leastat the beginning and end of each shift. If during thischeck the presence of the appropriate reference notch

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is not detected then all cylinders tested subsequent tothe last acceptance check shall be retested after theequipment has been reset.

B-3.2 Reference Standard

A reference standard of convenient length shall beprepared from a cylinder of similar diameter and wallthickness range, and from material with the sameacoustic characteristic and surface finish as the cylinderto be inspected. The reference standard shall be freefrom discontinuities which may interfere with thedetection of the reference notches.

Reference notches, both longitudinal and transverse,shall be matched on the outer and inner surface of thestandard. The notches shall be separated such that eachnotch can be clearly identified.

The following dimensions and shape of notches are ofcrucial importance for the adjustment of the equipment(see Fig. 16 and Fig. 17):

a) Length of the notches (E) shall be no graterthan 50 mm;

b) Width (W) shall be no grater than twice thenominal depth (T). However, where thiscondition cannot be met a maximum of 1mmis acceptable;

c) Depth of the notches (T) shall be 5 percent ±0.75 percent of the nominal thickness (S) witha minimum of 0.2 mm and a maximum of1 mm, over the full length of the notch.Runouts at each end are permissible;

d) Notch shall be sharp edged at it’s intersectionwith surface of the cylinder wall. The crosssection of the notch shall be rectangularexcept where spark erosion machiningmethods are used; then it is acknowledged thatthe bottom of the notch will be rounded; and

e) Shape and dimensions of the notch shall bedemonstrated by an appropriate method.

B-4 CALIBRATION OF EQUIPMENT

Using reference standard described in B-3.2, theequipment shall be adjusted to produce clearlyidentifiable indications from inner and outer referencenotches. The amplitude of the indications shall be asnear equal as possible. The indication of smallestamplitude shall be used as the rejection level and forsetting visual, audible, recording or sorting devices.The equipment shall be calibrated with the referencestandard or probe, or both, moving in the same manner,in the same direction and at the same speed as will beused during the inspection of the cylinder. All visual,audible, recording or sorting devices shall operatesatisfactorily at the test speed.

B-5 WALL THICKNESS MEASUREMENT

If the measurement of the wall thickness is not carriedout at another stage of production, the cylindrical partshall be 100 percent examined to ensure that thethickness is not less than the guaranteed minimum value.

B-6 INTERPRETATION OF RESULT

Cylinders with indications which are equal to or greaterthan the lowest of the indications from the referencenotches shall be withdrawn. Surface defects may beremoved; after removal the cylinders shall be re-subjected to ultrasonic flaw detection and thicknessmeasurement.

Any cylinder which is shown to be below theguaranteed minimum wall thickness shall be rejected.

B-7 CERTIFICATION

The ultrasonic testing shall be certified by the cylindermanufacturer. Every cylinder, which has passed theultrasonic testing in accordance with this standard shallbe stamp-marked with the symbol ‘UT’.

FIG. 16 DESIGN DETAILS AND DIMENSIONS OF THE

REFERENCE NOTCHES FOR LONGITUDINAL DEFECTS

Key1 — external reference notch2 — internal reference notch

NOTET ! (5 ± 0.75)% S but ! 0.2 mm ! T ! 1 mmW ! 2T but if not possible then W ! 1 mmE ! 50 mm

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NOTET ! (5 ± 0.75)% S but 0.2 mm ! T ! 1 mmW ! 2T, but if not possible then W ! 1 mm E ! 50 mm

FIG. 17 SCHEMATIC REPRESENTATION OF THE REFERENCE NOTCHES FOR CIRCUMFERENTIAL DEFECTS

C-1 The following procedure can be used to determinethe NDE defect size for metal lined hoop wrapped andmetal lined full wrapped designs:

a) Introduce internal flaws in the metallic liner.Internal flaws may be machined prior to theheat treatment and closing of the end of thecylinder;

b) Size these artificial defects to exceed thedefect length and depth detection capability

ANNEX C(Clauses 5.2.7, 6.3.4 and 7.3.4)

NDE DEFECT SIZE BY FLAWED CYLINDER CYCLING

of the NDE inspection method; andc) Pressure cycle to failure three cylinders

containing these artificial defects inaccordance with the test method specified inA-12.

If the cylinders do not leak or rupture in less than 1 000cycles multiplied by the specified service life in years,then the allowable defect size for NDE is equal to orless than the artificial flaw size at that location.

ANNEX D(Clauses 6.3.2, 7.3.2 and 8.3.2)

VERIFICATION OF STRESS RATIOS USING STRAIN GAUGES

D-0 This Annex describes a procedure that may beused to verify stress ratios by use of strain gauges.

a) The stress-strain relationship for fibre isalways elastic and therefore the stress ratiosand the strain ratios are equal.

b) High elongation strain gauges are required.c) Strain gauges should be orientated in the

direction of the fibre on which they are

mounted (that is with hoop fibre on the outside of the cylinder, mount gauges in the hoopdirection).

D-1 METHOD 1 (APPLIES TO CYLINDERSTHAT DO NOT USE HIGH TENSIONWINDING)

a) Prior to auto-frettage, apply strain gauges andcalibrate.

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b) Measure strains at auto-frettage, at zeropressure after auto-frettage and at workingand minimum burst pressure.

c) Confirm that the strain at burst pressuredivided by the strain at working pressuremeets the stress ratio requirements. Forhybrid construction, the strain at operatingpressure is compared with the rupture strainof cylinders reinforced with a single fibretype.

D-2 METHOD 2 (APPLIES TO ALL CYLINDERS)

a) At zero pressure after winding andauto-frettage, apply strain gauges andcalibrate.

b) Measure strains at zero, working andminimum burst pressures.

c) At zero pressure, after strain measurementshave been taken at the working and minimumburst pressure, and with strain gaugesmonitored, cut the cylinder section apart sothat the region containing the strain gauge isapproximately 125 mm long. Remove theliner without damaging the composite.Measure the strains after the liner is removed.

d) Adjust the strain reading at zero, operating,and minimum burst pressure by the amountof strain measured at zero pressure with andwithout the liner.

e) Confirm that the strain at burst pressuredivided by strain at working pressure meetsthe stress ratio requirements. For hybridconstruction, the strain at operating iscompared with the rupture strain of cylindersreinforced with a single fibre type.

ANNEX E(Clauses 6.4.5, 6.5.2.9, 7.4.5 and 7.5.2.9)

ENVIRONMENTAL TEST

E-1 GENERAL

This optional test is applicable to all types of cylinderscovered in this standard.

E-2 CYLINDER SET-UP AND PREPARATION

Two cylinders are tested in a condition representativeof installed geometry including coating (if applicable),brackets and gaskets, and pressure fittings using thesame sealing configuration (that is O-rings) as that usedin service. Brackets may be painted or coated prior toinstallation in the immersion test if they are painted orcoated prior to vehicle installation.

The cylinders are subjected to pre-conditioning inaccordance with E-3 and then exposed to a sequenceof environments, pressures and temperatures inaccordance with E-5.

Although pre-conditioning and fluid exposure isperformed on the cylindrical section of the cylinder,all of the cylinder, including the domed sections, shouldbe as resistant to the exposure environments as are theexposed areas.

As an alternative, a single cylinder approach may beused in which both the immersion environment andother fluids exposure tests are carried out on onecylinder. In this case, care should be taken to preventcross contamination among the fluids.

E-3 PRE-CONDITIONING

E-3.1 Pre-conditioning Apparatus

The following types of apparatus are needed for pre-conditioning the test cylinder by pendulum and gravelimpact.

a) Pendulum impact apparatus, comprising,1) an impact body of steel having the shape

of a pyramid with equilateral triangle facesand a square base, the submit and theedges being rounded to a radius of 3 mm;

2) a pendulum, the centre of percussion ofwhich coincides with the centre of gravityof the pyramid; its distance from the axisof rotation of the pendulum being 1 mand the total mass of the pendulumreferred to its centre of percussion being15 kg;

3) a means of determining that the energyof the pendulum at the moment of impactis not less than 30 N.m and is as close tothat value as possible; and

4) a means of holding the cylinder inposition during impact by the end bossesor by the intended mounting bracket.

b) Gravel impact machine, comprising,

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IS 15935 : 2011

1) an impact machine, constructedaccording to the design specificationsshown in Fig. 18 and capable of beingoperated in accordance with ASTMD3170 except that the cylinder may beat ambient temperature during gravelimpact; and

2) gravel, comprising alluvial road gravelpassing through a 16 mm space screenbut retained on a 9.5 mm space screen.Each application is to consist of 550 mlof graded gravel (approximately 250 to300 stones).

E-3.2 Pre-conditioning Procedure

E-3.2.1 Pre-conditioning for the ImmersionEnvironment Test

Pre-conditioning by both pendulum impact and gravelimpact is required for the portion of the containerto be used for the ‘immersion environment’ test(see E-4.1).

With the cylinder unpressurized, pre-condition thecentral section of the cylinder that will be submerged,by an impact of the pendulum body at three locationsspaced approximately 150 mm apart. Following

impact, pre-condition each of the three locations bygravel impact application.

Additionally, pre-condition a location within thesubmerged portion of each domed section and 50 mm(measured axially) from the tangent by a single impactof the pendulum body.

E-3.2.2 Pre-conditioning for the Other Fluid ExposureTest

Pre-conditioning by gravel impact only is requiredfor the portion of the container to be used for the ‘otherfluid exposure’ test (see E-4.2).

Divide the upper section of the cylinder used for the‘other fluids exposure’ test into 5 distinct areas ofnominal diameter 100 mm and mark these forpre-conditioning and fluid exposure (see Fig. 19).Ensure that the areas do not overlap on the cylindersurface and, for the single cylinder approach, do notoverlap the immersed section of the cylinder. Whileconvenient for testing, the areas need not be orientedalong a single line.

With the cylinder unpressurized, pre-condition eachof the 5 areas identified in Fig. 19 for other fluidexposure on the cylinder by gravel impact application.

Key1 — funnel2 — fuel container3 — air inlet4 — 50 mm pipe5 — cabinet approximately 500 mm wide6 — sizing screen

FIG. 18 GRAVEL IMPACT MACHINE

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IS 15935 : 2011

Key1 — other fluid exposure area2 — immersion area (lower third)

FIG. 19 CYLINDER ORIENTATION AND LAYOUT OF

EXPOSURE AREAS

E-4 ENVIRONMENTS

E-4.1 Immersion Environment

At the appropriate stages in the test sequence (see Table10) orient the cylinder horizontally to immerse thelower third of the cylinder diameter in a simulated andrain/road salt water solution composed of the followingcompounds:

a) Deionized water;b) Sodium chloride: 2.5 percent (mass fraction):

± 0.1 percent;c) Calcium chloride: 2.5 percent (mass fraction):

± 0.1 percent;d) Sulphuric acid: sufficient to achieve a solution

pH of 4.0 ± 0.2.

Adjust the solution level and pH prior to each test stepwhich uses this liquid.

Maintain the temperature of the bath at 21 ± 5°C.During immersion, hold the unsubmerged section ofthe cylinder in ambient air.

E-4.2 Other Fluid Exposure

At the appropriate stages in test sequence (see Table

10) expose each marked area to one of five solutionsfor 30 min. Use the same environment for each locationthroughout the test. The solutions are:

a) Sulphuric acid : 19 percent (volume fraction) aqueous solution;

b) Sodium hydroxide : 25 percent (mass fraction) aqueous solution;

c) Methanol/gasoline : 30/70 percent con-centrations;

d) Ammonium nitrate : 29 percent (mass fraction) aqueous solution; and

e) Windscreen washer fluid.

During the exposure, orient the test cylinder with theexposure area uppermost. Place a pad of glass woolone layer thick (approximately 0.5 mm) and trimmedto the appropriate dimensions on the exposure area.Using a pipette, apply 5 ml of the test fluid to the glasswool. Ensure that the pad is wetted evenly across itssurface and through its thickness. Pressurize thecylinder and remove the gauge pad after pressurizationfor 30 min.

E-5 TEST CONDITIONS

E-5.1 Pressure Cycle

At the appropriate stage in the test sequence (see Table10), subject the cylinder to hydraulic pressure cyclesof between 20 bar and 260 bar for the ambient andhigh temperature steps, and between 20 bar and 160 barfor the lower temperature steps. Hold the maximumpressure for a minimum of 60 s and ensure that eachfull cycle takes no less than 66 s.

E-5.2 High and Low Temperature Exposure

At the appropriate stages in the test sequence (see Table10), bring the surface of the cylinder to a high or low

Table 10 Test Conditions and Sequence(Clauses E-4.1, E-4.2, E-5.1 and E-5.2)

Test Steps

Two Cylinder Approach Single Cylinder Approach

Immersion cylinder

Other fluids

Alternative single cylinder

Environments Number of Pressure Cycles

Temperature

— 1 1 Other fluids (40 min) — Ambient 1 — 2 Immersion 500 × service life (years) Ambient — 2 — Air 500 × service life (years) Ambient — 3 3 Other fluids (40 min) — Ambient 2 4 4 Air 250 × service life (years) Low — 5 5 Other fluids (40 min) — Ambient 3 6 6 Air 250 × service life (years) High

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temperature in air. The low temperature shall be nohigher than – 35°C and the high temperature shall be82 ± 5°C as measured on the surface of the cylinder.

E-6 TEST PROCEDURE

The test procedure is as follows:

a) Pre-condition the cylinders (or cylinder in thesingle cylinder approach) in accordancewith E-3.2;

b) Carry out the sequences of environmentalexposure, pressure cycling and temperature

exposure as defined in Table 10; do not washor wipe the cylinder surface between stages;and

c) Following completion of the sequences,subject the cylinders (or cylinder) to ahydrostatic pressure burst test to destructionin accordance with A-11.

E-7 ACCEPTABLE RESULTS

The test is considered to be satisfied if the burst pressureof the cylinders (or cylinder) is no less than 1.8 timesthe service pressure.

ANNEX F(Informative)

MANUFACTURER’S INSTRUCTIONS FOR HANDLING, USE ANDINSPECTION OF CYLINDERS

F-1 GENERAL

The primary function of the manufacturer’s instructionsis to provide guidance to the cylinder purchaser,distributor, installer and user for the safe use of thecylinder over its intended service life.

F-2 DISTRIBUTION

The manufacturer should advise the purchaser tosupply these instructions to all parties involved in thedistribution, handling, installation and use of thecylinders.

The document may be reproduced to provide sufficientcopies for this purpose; however, it should be markedto provide reference to the cylinders being delivered.

F-3 REFERENCE TO EXISTING CODES,STANDARDS AND REGULATIONS

Specific instructions may be stated by reference tonational or recognized codes, standards andregulations.

F-4 CYLINDER HANDLING

Handling procedures should be described which wouldensure that the cylinders will not suffer unacceptabledamage or contamination during handling.

F-5 INSTALLATION

Installation instructions should be provided whichwould ensure that the cylinders do not suffer

unacceptable damage during installation and duringnormal operation over the intended service life.

Where the mounting is specified by the manufacturer,the instructions should, where relevant, contain detailssuch as mounting design the use of the resilient gasketmaterials, the correct tightening torques and avoidanceof direct exposure of the cylinder to the environment,chemicals and mechanical contacts. Cylinder locationsand mountings should comply with recognizedinstallation standards.

Where the mounting is not specified by themanufacturer, the manufacturer should draw thepurchaser’s attention to possible long term impactsof the vehicle mounting system, for example vehiclebody movements and cylinder expansion/contractionunless the pressure and temperature conditions ofservice.

Where applicable the purchaser’s attention should bedrawn to the need to provide installations such thatliquids or solids cannot be collected to cause cylindermaterial damage.

The correct pressure relieve device to be fitted shouldbe specified.

Cylinder valves, pressure relief of devices andconnections should be protected against breakage in acollision. If this protection is the cylinder the decisionand method of attachment should be approved by thecylinder.

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ANNEX G(Foreword)

COMMITTEE COMPOSITION

Gas Cylinders Sectional Committee, MED 16

Organization Representative(s)

Petroleum and Explosive Safety Organization, Nagpur SHRI AJAI NIGAM (Chairman)SHRI D. K. GUPTA (Alternate)

All India Industrial Gases Manufacturers Association, New Delhi SHRI KARAN BHATIA

SHRIMATI VEENA PETER (Alternate )

Bharat Petroleum Corporation Ltd, Mumbai SHRI THARIYAN GEORGE

SHRI SANJAY PHULLI (Alternate )

Bharat Pumps and Compressors Ltd, Allahabad SHRI J. P. SINHA

SHRI P. G. CHOUDHURY (Alternate)

BOC India Ltd, Kolkata SHRI K. MANOHARAN

SHRI RAMANA VUTUKURU (Alternate)

Everest Kanto Cylinder Ltd, Mumbai SHRI P. M. SAMVATSAR

SHRI A. K. KHAMKAR (Alternate)

Hindustan Petroleum Corporation Ltd, Mumbai SHRI P. P. NADKARNI

SHRI ALOK KUMAR GUPTA (Alternate)

Indian Oil Corporation Ltd, Mumbai SHRI S. S. SAMANT

SHRI RAJESH HAZARNIS (Alternate)

International Industrial Gases Ltd, Kolkata SHRI DEVENDRA K. GARG

SHRI NIKHILESh K. GARG (Alternate)

Kabsons Gas Equipments Ltd, Hyderabad SHRI SATISH KABRA

SHRI S. GOPALAIAH (Alternate)

Kosan Industries Ltd, Mumbai/Surat SHRI S. K. DEY

SHRI S. B. BOMAL (Alternate)

LPG Equipment Research Centre, Bangalore SHRI G. P. GUPTA

SHRIMATI KAROBI MUKHERJEE (Alternate)

Mahanagar Gas Limited, Mumbai SHRI RAGHUNATH KULAI

SHRI ARUN NAYAK (Alternate)

Maruti Koatsu Cylinders Ltd, Mumbai SHRI NITIN J. THAKKAR

SHRI A. S. SARAN (Alternate)

Ministry of Defence (DGQA), Pune SHRI J. P. TIWARI

LT-COL B. V. RAVI KUMAR (Alternate)

Praxair India Ltd, Bangalore SHRI MILAN SARKAR

SHRI ARINDAM DAS (Alternate)

Research & Development Estt (Engineers), Pune SHRI P. K. CHATTOPADHYAY

SHRI A. BASU (Alternate)

Sakha Engineers Pvt Ltd, New Delhi SHRI AMARJIT S. KOHLI

SICGIL India Ltd, Chennai SHRI FAROOQUE DADABHOY

SHRI R. PADMANABAN (Alternate)

Steel Authority of India Ltd, Salem SHRI T. KALYANASUNDARAM

SHRI N. K. VIJAYAVARGIA (Alternate)

Steel Authority of India Ltd, Ranchi SHRI DEBASHIS KARMAKAR

DR B. K. JHA (Alternate)

Supreme Cylinders Ltd, Delhi SHRI M. L. FATHEPURIA

Tekno Valves, Kolkata SHRI Y. K. BEHANI

SHRI R. BEHANI (Alternate)

Trans Valves (India) Pvt Ltd, Hyderbad SHRI A. K. JAIN

SHRI ANUJ JAIN (Alternate)

Vanaz Engineers Ltd, Pune SHRI S. K. KHANDEKAR

SHRI S. R. SARVATE (Alternate)

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Organization Representative(s)

In personal capacity (Menon & Patel, 14/1, Mile, Mathura Road, SHRI EBRAHIM M. PATEL

Faridabad)

In personal capacity (303, Shantikunj, Pandav Bunglows Lane SHRI L. D. THAKKAR

Athwalines, Surat)

BIS Directorate General SHRI C. K. VEDA, Scientist ‘F’ and Head (MED)[Representing Director General (Ex-officio)]

Member SecretarySHRI VISHAL TOMER

Scientist ‘C’ (MED), BIS

Dissolved Acetylene Cylinders, Generators, Acetylene Pipe Lines and High PressureGas Cylinders Subcommittee, MED 16 : 3

BOC India Ltd, Kolkata SHRI VUTUKURU RAMANA (Convener)

Al-Can Exports Pvt Ltd, Distt Thane SHRI VIJAY K. PARIKH

SHRI D. C. DAVE (Alternate)

All India Industrial Gases Manufacturers Association, New Delhi SHRI KARAN BHATIA

SHRIMATI VEENA PETER (Alternate)

Bharat Pumps and Compressors Ltd, Allahabad SHRI J. P. SINHA

SHRI P. G. CHOUDHURY (Alternate)

Everest Kanto Cylinder Ltd, Mumbai SHRI P. M. SAMVATSAR

SHRI. A. G. KHAMKAR (Alternate)

Hindalo Industries Limited, Mumbai SHRI SUBHANKAR GUPTA

SHRI S. DEVADOSS (Alternate)

International Industrial Gases Ltd, Howrah SHRI D. K. GARG

SHRI N. K. GARG (Alternate)

Jai Maruti Gas Cylinders Gases Ltd, Gwalior SHRI ASHOK K. NIGAM

SHRI VAISHNAV NIGAM (Alternate)

Klas Technology Ventures Ltd, Bangalore SHRI K. G. KRISHNAMURTHY

SHRI K. J. KULKARNI (Alternate)

KVK Corporation, Mumbai SHRI R. CHANDGOTHIA

SHRI V. CHANDGOTHIA (Alternate)

Mahanagar Gas Limited, Mumbai SHRI RAGHUNATH KULAI

SHRI ARUN NAYAK (Alternate)

Maruti Koatsu Cylinders Ltd, Mumbai SHRI NITIN J. THAKKAR

SHRI A. S. SARAN (Alternate)

Ministry of Defence (DGQA), Pune SHRI J. P. TIWARI

LT COL RAVI KUMAR (Alternate)

Petroleum and Explosive Safety Organization, Nagpur SHRI AJAI NIGAM

SHRI D. K. GUPTA (Alternate)

Praxair India Ltd, Bangalore SHRI MILAN SARKAR

SHRI ARINDAM DAS (Alternate)

Rama Cylinders Pvt Ltd, Mumbai SHRI SANJAY R. NAPHADE

SHRI SANJAY S. MANDE (Alternate)

SICGIL India Ltd, Chennai SHRI RUQSHAD DADABHOY

SHRI R. PADMANABAN (Alternate)

Strategic Engineering (P) Ltd, Chennai DR M. RAMAKRISHNA

SHRI G. S. VISWANATH (Alternate)

Tekno Valves, Kolkata SHRI Y. K. BEHANI

SHRI R. BEHANI (Alternate)

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Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standardsshould ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of‘BIS Catalogue’ and ‘Standards : Monthly Additions’.

This Indian Standard has been developed from Doc No.: MED 16 (0815).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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Published by BIS, New Delhi

AMENDMENT NO. 1 JUNE 2013

TO

IS 15935 : 2011 COMPOSITE CYLINDERS FOR

ON-BOARD STORAGE OF COMPRESSED NATURAL

GAS (CNG) AS A FUEL FOR AUTOMOTIVE VEHICLE —

SPECIFICATION

[Page 37, clause A-7 (c), line 1] — Substitute ‘-20°C’ for ‘- 40°C’.

[Page 37, clause A-7 (d), line 3] — Substitute ‘-20°C’ for ‘- 40°C’. (MED 16)

Reprography Unit, BIS, New Delhi, India

Documents

IS 15935 (2011): Composite Cylinders for on-board Storage ...impregnated continuous filament wound over a metallic or non-metallic liner. NOTE — Composite cylinders using non-metallic