FABRICATION OF STORAGE BUFFER VESSEL

BY

NISHANT RAO BODDEDA

ID NO (10101812)

Goals and Targets To learn, understand and to practically observe the machinery used, the design aspects inculcated and the fabrication processes involving Pressure Vessels (work order 558601-558602)

To practically indulge myself in all possible ways to gain the knowledge about tasks undertaken by the production units and the feeder shops.

To learn the welding technologies used for various materials and techniques involved in welding.

To learn the Non Destructive Testing methods used for quality inspection of all the materials during the course of their manufacture.

INTRODUCTION TO BHPV

PRODUCTION SECTOR:The Shop is divided into two main categories such as:•Feeder shop•Assembly shop

With the Board for Industrial and Financial Reconstruction’s (BIFR) sanction of the Modified Draft Rehabilitation Scheme envisaging merger of Bharat Heavy Plate and Vessels Limited (BHPV) with the Maharatna company Bharat Heavy Electricals Limited (BHEL), BHPV has become the 17th manufacturing unit of BHEL. The unit will hereafter be named as Heavy Plates and Vessels Plant (HPVP), Vishakhapatnam. The Appointed date for the merger is 1st October 2011. Till now, BHPV was a wholly owned subsidiary of BHEL. After the Union cabinet’s approval in February 2013, the merger scheme was filed with BIFR in March 2013 and the entire merger exercise was completed in a record time of 5 months thereafter. The merger will pave the way for BHEL in further diversifying its product portfolio. HPVP derives strength from numerous esteemed references in the Oil, Steel, Cement & Fertilizer sectors. Compact Heat Exchangers for the Light Combat Aircraft ‘Tejas’ meeting all technical requirements mandated by the relevant Military Standards of Govt. of India will continue to be manufactured at HPVP.

M.P : Material Preparation L.M.S: Lathe Machine Shop H.M.S: Heavy Machine Shop Press: Press Shop SH: Shells Shop Nozzle: Nozzle Section

Feeder Shop: The parts that are used for assembling in production shop are made in feeder shops. The feeder shops are of six types:

Assembly Shop: The parts are being assembled at the shop. The parts are prepared at the feeder shop. There are mainly five assembly shops:

H.E: Heat Exchangers P.V: Pressure Vessels C.P: Cryogenic Production C.S.P 1: Combustion System Products 1. C.S.P 2: Combustion System Products 2.

A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the gauge pressure.

Pressure Vessels are defined in ASME Section VIII, Div 1 & 2 introduction:

“ Pressure Vessels are containers for the containment of pressure either external or internal. The pressure may be obtained from an external source, or by the application of heat from a direct or indirect source, or any combination of both.”

DEFINITION

CLASSIFICATION OF PRESSURE VESSELS

Based on Manufacturing Methods:1) Welded Vessels2) Forged Vessels3) Multiwall Vessels4) Multiwall Wrapped Vessels5) Band Wrapped Vessels Based on Manufacturing

Materials:1) Steel Vessels2) Non Ferrous Vessels3) Non Metallic Vessels Based on Geometric Shapes:1) Cylindrical Vessels2) Spherical Vessels3) Rectangular Vessels

4) Combined VesselsBased on Installation Methods:1) Vertical Vessels2) Horizontal Vessels Based on Pressure-Bearing Situation:1) Internal Pressure Vessels2) External Pressure Vessels Based on Wall Thickness:1) Thin Wall Vessel2) Thick Wall Vessel Based on Technological Processes:1) Reaction Vessel2) Heat Exchanger Vessel3) Separation Vessel4) Storage Container Vessel

Based on Operating Temperature:1) Low Temperature Vessels(less than or equal to -

20°C)2) Normal Temperature Vessels(Between -20°C to

150°C)3) Medium Temperature Vessels(Between 150°C to

450°C)4) High Temperature Vessels(more than or equal to

450°C) Based on Design Pressure:1) Low Pressure Vessels(0.1MPa to 1.6MPa)2) Medium Pressure Vessels(1.6MPa to 10MPa)3) High Pressure Vessels(10MPa to 100MPa)4) Ultra High Pressure Vessels(More than 100MPa) Based on Usage Mode:1) Fixed Pressure Vessel2) Mobile Pressure Vessel

TYPICAL COMPONENTS

1. Cylindrical or Spherical shell 2. Formed Heads(Dished ends)3. Blind Flanges, Cover Plates,

Flanges4. Openings And Nozzles5. Supports

ASME CODES USED FOR PRESSURE VESSELS

The BHPV company strictly abides by the“ASME SECTION VIII DIVISION 1” & “ASME SECTION VIII DIVISION 2”(ASME Boiler and Pressure Vessel Code) for fabrication and quality testing methods of pressure vessels.

ASME BPVC Section II:Part A - Ferrous Material SpecificationsPart B - Nonferrous Material SpecificationsPart C - Specifications for Welding Rods, Electrodes, and Filler MetalsPart D - Properties (Customary)Part D - Properties (Metric)•ASME BPVC Section V - Non destructive Testing.

DESIGN CRITERIA AT BHPV Selection Of The Type Of Vessel:i. The operating temperature and

pressure. ii. Function and location of the vessel.iii. Nature of fluid.iv. Necessary volume for storage or

capacity for processing Design Loads Materials Allowable Stress

DESIGN CONSIDERATION

•Internal and external pressure.•Self-weight.•Static reactions from the attached components.•Cyclic and Dynamic reactions due to pressure or thermal variations.•Wind Pressure and Seismic forces.•Impact reaction due to fluid shock.

DESIGN SOFTWAREThe company is mainly using PV Elite software for the design of Pressure Vessel.

PV Elite is a comprehensive program for the complete structural design or analysis of pressure vessels according to latest standards from ASME.

PV Elite evaluates the entire vessel, analyzing the effects of vessel deadweight and bending due to wind and seismic loads.

The main objective:•To analyze the safety parameters for allowable working pressure using PV Elite which comply to ASME VIII standard.•To fabricate the pressure vessel as per the reference standards.

PURCHASE OBJECTIVE of BHPV:

The main objective of procurement activity is to purchase the required materials, equipment and related or associated services, at the right time, at an optimum price, consistent with quality requirements, with transparency in order to adhere to commitments made to customers.

Planning and Technology:Planning and Technology department prepares Master Technology, Route card and Job cards for the Work-order as per the design.

Route card: This card indicates the details of operations that are needed to be carried out in the production shop. This helps the operator to decide the sequence of operations and machining tools that are needed.

Master Technology: This indicates the technology involved in the fabrication of work order. Details about the material, machinery etc are prepared on this card.

Job card: This card is prepared and provided to each and every section in the production shop. It gives detail to the worker who is working on the job. Various operations and machine tools needed as per dimension are provided on it. The time spent by the worker for doing the operation is explained in detail.

ORDER OF FABRICATION

Bevelling of metal plates Rolling into shells Welding into Longitudinal seam Re-rolling Welding into circumferential seam Cutting slots for nozzles and fitments Machining and grinding Welding the nozzles and fitments

NON DESTRUCTIVE TESTING

Non –destructive testing is one of the part of the function of quality function.By defining non destructive testing is the testing of materials, for surface or internal flaws or metallurgical conditions.

Being a high technology concept, evolution of the equipment has made it robust enough for application in any industrial environment at any stage of from steel making to applying site inspection of components already in service. A certain degree of skills is required to apply the technique properly with consequent feed back to the production facility.

Non-destructive testing is not just a method for rejection standard material it is also an assurance that the supposedly good to good.

There are basically many types of destructing test are held in the shops but in BHPV there are four major types of tests done on Pressure Vessels those are as follows:-

1) Radiography2) Magnetic particle crack detection3) Dye penetrate testing4) Ultrasonic flaw detection

RADIOGRAPHY TESTING:

Radiographic Testing (RT), or industrial radiography, is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials.

Either an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137) can be used as a source of photons. Neutron radiographic testing (NR) is a variant of radiographic testing which uses neutrons instead of photons to penetrate materials. This can see very different things from X-rays, because neutrons can pass with ease through lead and steel but are stopped by plastics, water and oils.

Since the amount of radiation emerging from the opposite side of the material can be detected and measured, variations in this amount (or intensity) of radiation are used to determine thickness or composition of material. Penetrating radiations are those restricted to that part of the electromagnetic spectrum of wavelength less than about 10 nanometers.

Procedure:

•Select the object to be tested under radiography.•Clean/grind the weld surface to remove any irregularities.•Depending upon the maximum length of the film available divide weld into no of parts.• Depending upon the material type and thickness suitable isotope or X-ray voltage is selected.•Now place the film on the surface of work piece with the help of magnetic clips in such a way that work piece comes in between source and film.•A lead symbol ‘B’ with minimum dimensions of ½ inch in height and 1/16 in thickness is attached to the back of each film holder to determine whether back scatter radiation is exposing the film.•Now the source to film distance is decided and required voltage and current are applied and source is transferred to site using a remote.•Work piece is exposed to Source for a required time.•Now cut the film as per required length and keep it between lead screens and place it in a film holder.Now the film is analyzed in the dark room and various defects are noted. •Now stick lead letters indicating date, work order number on the corners of the work piece so that they will be reflected on the film.

MAGNETIC-PARTICLE INSPECTION

Magnetic particle inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and subsurface discontinuities in ferrous materials. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electrical current is passed through the test object and a magnetic field is formed in the material. Indirect magnetization occurs when no electrical current is passed through the test object, but a magnetic field is applied from an outside source. The magnetic lines of force are perpendicular to the direction of the electrical current which may be either alternating current (AC) or some form of direct current (DC) (rectified AC).

The presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak. Ferrous iron particles are applied to the part. The particles may be dry or in a wet suspension. If an area of flux leakage is present the particles will be attracted to this area. The particles will build up at the area of leakage and form what is known as an indication. The indication can then be evaluated to determine what it is, what may have caused it, and what action should be taken if any.

ULTRASONIC TESTING:

In ultrasonic testing (UT), very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz and occasionally up to 50 MHz are launched into materials to detect internal flaws or to characterize materials. The technique is also commonly used to determine the thickness of the test object, for example, to monitor pipe work corrosion.Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is a form of non-destructive testing used in many industries including aerospace, automotive and other transportation sectors.

Working Principle:In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a coolant (such as oil) or by water, as in immersion testing.

There are two methods of receiving the ultrasound waveform, reflection and attenuation. In reflection (or pulse-echo) mode, the transducer performs both the sending and the receiving of the pulsed waves as the “sound” is reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the object or from an imperfection within the object.

DYE PENETRANT INSPECTION:

Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials, but for inspection of ferrous components magnetic-particle inspection is preferred for its subsurface detection capability.

LPI is used to detect casting and forging defects, cracks, and leaks in new products, and fatigue cracks on in-service components.Inspection Steps:

1. Pre-cleaning:

The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may “work over” small discontinuities in the part, and an etching bath is recommended as a post-bath treatment.

2.Application of Penetrant:The penetrant is then applied to the surface of the item being tested. The penetrant is allowed time to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being testing and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.

3.Excess Penetrant Removal:The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray.

4.Application of Developer:After excess penetrant has been removed a white developer is applied to the sample. Several developer types are available, including: non-aqueous wet developer, dry powder, water suspend able, and water soluble. Choice of developer is governed by penetrant compatibility (one can’t use water-soluble or suspend able developer with water-washable penetrant), and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspend able developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface.

Bill of materialA bill of materials is a list of the raw materials, sub-assemblies, intermediate assemblies, sub-components, parts and the quantities of each needed to manufacture an end product.

Creating a Bill of Materials should include:•BOM Level•Part Number•Part Name•Phase•Description•Quantity•Unit of Measure•Procurement Type•Reference Designators•BOM Notes

WELDING PROCEDURE SEQUENCE (WPS)

A WPS is a document that describes how welding is to be carried out in production. They are recommended for all welding operations and many application codes and standards make the mandatory.

WPS information required is generally similar to that recorded on a Procedure Qualification Record (PQR) or Welding Procedure Approval Record (WPAR), except that ranges are usually permitted on thicknesses, diameters, welding current, materials, joint types etc.If a WPS is used in conjunction with approved welding procedures then the ranges stated should be in accordance with the approval ranges permitted by the welding procedure.However careful consideration should be given to the ranges specified to ensure they are achievable, as the ranges given by welding procedure standards do not always represent good welding practice.

Fabrication Procedure A shell is made from a metal plate of the required dimension and required material. The plate is cut to the required length and breadth and later on all four sides a bevel is prepared as per the drawing. The square cutting and the bevel preparation is carried out by oxyacetylene flame for carbon steels and plasma arc process for stainless and high alloy steels. The cut edges are then ground back to sound metal by 1 to 1.5 mm so that all the adversely affected material in the cut zone is removed. The dressed are then examined for defects due to incorrect cutting parameters. If irregularities are found the surface is cleaned and again dressed. The plate is now ready for bending; once the shell is fed to the bending machine, first both ends are pressed to the required shape by the rollers. This is called Prepinging. After prepinging, the profile at the ends is checked using a template, and if satisfactory, full bending is carried out. Usually, the bending is carried out in a few stages so that the elongation is negligible and no further trimming of the plate is needed.

Now the shells after bending is joined to its ends by the process called longitudinal seam welding or L-seam welding. It is a butt weld with full penetration and the electrode used is E7018 which is a low alloy and high tensile steel electrode.

The following sequence of operations is done for the joining of shells.•ASSEMBLY•Arrange the shells on the rollers or roller positioners.•Measure the circumference of the mating parts•Grind the bevels of the mating parts to bright metal•Mark the orientation lines on shell with respect to L-seam welds.•Set the shells together and match as per orientation•Assemble and tack weld the shells from outside as per approved Welding Procedure Specification and maintain a uniform gap up to 2 mm maintaining tack weld length, weld size pitch

•GOUGING Gouge out the clamps welded on the shell for assembly. Do not dig out the parent material.•GRINDING Grind the clamps removed areas to smoothness. Grind the bevel from inside to remove spatter penetrated due to tack welding from outside and sander 50 mm on either side of the joints.•Manual arc welding (MAW) Weld the joint between the shells with two layers from inside to get 5 mm weld layer with approved WPS. De slag the top surface thoroughly.•Submerged arc welding (SAW) Submerge arc weld the joint between shells with approved WPS and complete it.

•Back Gauging Back gouge from outside to sound metal circumference.•Grinding Grind the Back gouge area from outside to sound metal circumference.•Dye Penetration test Conduct D.P. test on Back gouge portion if required by inspection.•Welding Weld manually one layer on the joint between the shells with approved WPS and de-slag the top surface thoroughly.•Submerged Arc Welding Submerge arc weld from outside of the joint between the shells with approved WPS and de slag the top surface thoroughly.•Grinding Grind the circumferential weld from inside and outside to smoothness.•Manual Arc Welding (MAW) Rectify the spots by build-up on the joints between shells with approved WPS.•Grinding Grind the built up spot to smoothness.•D.P. Test Conduct D.P. test•Radiography Conduct 100% radiography on circumferential joint.

Dished ends:A vessel dished end is a concave end of a vessel. Vessel dished ends are mostly used in storage or pressure vessels in industry. These ends, which in upright vessels are the bottom and the top, use less space than a hemisphere (which is the ideal form for pressure containments) while requiring only a slightly thicker wall.The manufacturing of such an end is easier than that of a hemisphere. The starting material is first pressed to a radius r1 and then curled at the

edge creating the second radius r2. Vessel dished ends can also

be welded together from smaller pieces. There is no compulsion that all the industries should go for the same type of dish ends or spheres (including sizes). Hence we need different types and sizes of tools while manufacturing the plates.

Shell to Shell Assembly:Any completed shell shall have a reference centerline on the shell, which shall be marked at least in 0º, 90º, 180º and 270º and shall extend through the full length of the shell. Consider a shell with only one longitudinal seam whose circularity is maintained satisfactorily by providing spiders at both the open ends. Obviously the seam can be made a reference line. However to mark the same on the shell, the following methodology shall be adopted.1. Put a centre punch on the centre of the weld at one end of the shell.2. Stretch a measuring tape from there and measure the outside circumference of the shell at that end.3. Divide by 4 to get one-quarter measurement and mark it along the circumference to obtain 90º, 180º and 270º at the same end. The difference in dimension of each quarter shall be limited to 2 or 3 mm maximum, depending on the internal diameter of the vessel.4. Transfer the centre punch put on the centre of the weld at one end of the shell to the other end. The rotators are to be leveled by adjusting the rollers at both ends separately.5. Make the same divisions at this end also.6. Connect these points to obtain the four centerlines which will be the four major longitudinal axis of the shell.7. The same methodology has to be repeated for all the shells.

Shell to dished end Assembly:

The axis on the shell is marked as specified in drawing. In order to align the end to shell, the centre point and the four circumferential points on the head have to be marked. This is done as follows:1. At the straight face of the end, take the outer circumference and locate the four centre points by dividing the circumference by 4.2. Put the dish end upside-down on the thick levelled plate and place two tri-squares at opposite centre-points marked. Stretch a chalked thread on top just gracing the top most point on the dish end to put am impression of the line. Repeat the same at 90º to the first line, which will result in a point that is the centre of the dish end.3. Connect the four centre-points representing 0º, 90º, 180º and 270º to the centre of the dish end.4. By the same method, any angle on the dish end can be located for the placement of nozzles or other attachments.As per drawing, Proper assembly is only possible by having a dimension check of the diameter of shell and the circumference of the dished end, and then only assembly is done.

Fitting of Subassemblies:

Marking of the centre of attachment and cutting line:The marking of all the attachments like the nozzles, manholes, and other fittings are preferably to be done simultaneously so that any fouling of these components with existing weld seams or among them could be checked. This is checked with respect to orientation plan/ elevation for vertical vessels and end view/ elevation for horizontal vessels.

Suppose a nozzle is provided at an angle of 350. Measure the outside circumference of the shell approximately at the position where the nozzle is to be fitted. This corresponds to 3600. Proportionately, the outside circumference to 350 is C x (35/360). Measure out this from the reference centerline at 00 and mark a parallel line at 350. The location of the nozzle can be anywhere on this line. Mark out the distance of 1500 mm according to drawing. Take the reference tangent line to locate the centre-point of the nozzle. Later the cutting line of the opening is also marked taking into consideration the curvature of the shell and that of the nozzle.

HYDRO-TESTING After stress relieving, the vessel has to be tested for any leakage. Water displaces air and chances are there for Air-Locks to form. This is very dangerous and could lead to bursting of vessel. The pressure is kept for 6 to 8 hours. A testing pressure of 1.3 times the design pressure is acceptable as per the drawing. The pressure should be increased in steps of 1/10 of the test pressure as it takes some time for stabilization. Mostly the vessel is kept horizontal so that proper inspection of the weld can be done while testing.The Vessel is completely filled with water such that the building up of pressure is very fast. Air vents are provided at high points to prevent air locking. The pressure gauge is attached at the topmost point and two gauges are attached.

SAND-BLASTING

Sandblasting is a act of propelling very fine bits of material at high-velocity to clean or etch a surface. Sand used to be the most commonly used and other materials are now used in its place. Any small, relatively uniform particles will work, such as steel grit, copper slag, walnut shells, powdered abrasives, even bits of coconut shell. Due to the dangers of inhaling dust during the process, sandblasting is carefully controlled, using an alternate air supply, protective wear, and proper ventilation.This process is used to remove the dust and rust from top layer of the vessel to facilitate for proper painting process. There is a pressure tank that supplies pressurized air to offer drum that is filled with copper slag, then the pipe with nozzle end is attached to offer drum. The copper slag comes in contact to the Vessel with a lot of force and scrapes away the rust leaving a clean and shiny surface nozzle.

ACTIVITIES/ACHIEVEMENTS Getting to know the work orders. L-seam welding of shells. Cold rolling on 50mm bending rolling machine. Assembly of shells. Radiography Test. Quality inspection of Shells. Calculation of volume of Ellipsoidal Dished End. Determining the length of sheet for rolling.

General mechanical maintenance Hydraulic Press , LMS & HMS shops. L-seam welding prior rolling Magnetic Particle test HMT CNC deep hole drilling machine Hydro-testing of shells Quality control & Inspection of Shells Study of Shells Welding of Shells. Marking of Shells