Global Pipe Australia Pty Ltd - HOBAS GRP Pipe Systems · Global Pipe Australia Pty Ltd has requested that GHD Pty Ltd prepare a ... thickness of the pipe, and the stress concentration

Global Pipe Australia Pty Ltd

Report for HOBAS PipeDurability Assessment

August 2011

Page 2 of 2341/24328/424573 HOBAS PipeDurability Assessment

This Report: has been prepared by GHD for Global Pipe Australia Pty Ltd and may only be usedand relied on by Global Pipe Australia Pty Ltd for the purpose agreed between GHD and GlobalPipe Australia Pty Ltd as set out in section 2 of this Report.

GHD otherwise disclaims responsibility to any person other than Global Pipe Australia Pty Ltdarising in connection with this Report. GHD also excludes implied warranties and conditions, tothe extent legally permissible.

This Report must not, without the prior written consent of GHD, be relied on by any other entityor person.

The services undertaken by GHD in connection with preparing this Report were limited to thosespecifically detailed in the Report and are subject to the scope limitations set out in the Report.

The opinions, conclusions and any recommendations in this Report are based on conditionsencountered and information reviewed at the date of preparation of the Report. GHD has noresponsibility or obligation to update this Report to account for events or changes occurringsubsequent to the date that the Report was prepared.

The opinions, conclusions and any recommendations in this Report are based on assumptionsmade by GHD described in this Report (refer sections 2, 3, 4 and 5). GHD disclaims liabilityarising from any of the assumptions being incorrect

GHD has prepared this Report on the basis of information provided by Global Pipe Australia PtyLtd and additional sources of literature, which GHD has not independently verified or checkedbeyond the agreed scope of work. GHD does not accept liability in connection with suchunverified information, including errors and omissions in the Report which were caused by errorsor omissions in that information.


Contents

1. Executive Summary 4

2. Background 5

3. Product 6

3.1 Pipe Material 6

3.2 Joints 7

4. Project Requirements 9

4.1 Design Life Duration 9

4.2 Design Life Definition 9

4.3 How Pipelines Fail 9

5. Exposure Conditions 10

6. Effect of Exposure Conditions on Product 12

6.1 Chemical Environment 12

6.2 Long Term Loads (and Effect of Creep) 13

6.3 Strain Corrosion 14

6.4 Cyclic or Repeated Load (Fatigue) 14

6.5 Biological Conditions & Tree Roots 14

6.6 Abrasion including Water Jet Cleaning 15

6.7 Stray Currents 16

6.8 UV (Sunlight) 16

6.9 Temperature 16

7. Summary Durability Assessment 19

8. References 22


1. Executive Summary

Global Pipe Australia Pty Ltd has requested that GHD Pty Ltd prepare a durability report for HOBASjacking pipe for sewer use with a focus on design life. A desktop durability analysis was conductedincluding a review of existing literature and test data.

Sewers are typically required to be 100 year life buried assets and thus the durability over 100 years wasassessed. Failure was defined as the point at which deterioration progresses to a level that makes thestructure unsafe or unserviceable; or when the level of maintenance necessary to maintain thefunctionality of the structure becomes uneconomical. Typically for pipelines this means structural failureor leakage.

This durability assessment has examined the conditions expected in underground sewer pipes andanalysed the effects of these on HOBAS jacking pipe system. It is recognised that poor water jet cleaningpractices could cause damage to pipes as can excessive ground movement. Under normal sewerconditions (chemical environment, loads, abrasives, tree roots incursion) this study has found that anexpected design life of HOBAS jacking pipe system of at least 100 years is reasonable. As differentconditions affect durability and thus design life, an assessment of project specific conditions needs to beundertaken to confirm the suitability of HOBAS jacking pipe for each application.


2. Background

Global Pipe Australia Pty Ltd is an importer of pipe for companies throughout Australia. One of theproducts imported is HOBAS jacking pipe for use in pressure water, sewage and drainage applications.

For a recent sewage pipe installation project in Queensland, for QLD Urban Utilities, HOBAS jacking pipehas been excluded from the preferences. For this project the design life of this pipe has come underconsideration. An important question is whether the design life of HOBAS is 50 years or closer to 100years.

Global Pipe Australia Pty Ltd has requested that GHD Pty Ltd prepare a durability report for HOBASjacking pipe. Of particular interest is the design life of the pipe. A durability analysis was conducted in theform of a desktop analysis of existing literature and test data. No physical research or testing work wasundertaken as part of this project.

The purpose of this report is to assess the durability of HOBAS pipe. It has been assumed that at thebeginning of its life the pipe, joints and fittings were free of faults due to manufacturing, packing,transport, delivery and installation. It also assumes that the pipeline was specified and supplied correctlyfor the loads and other conditions due to operation and maintenance and were installed in accordancewith good practice.


3. Product

3.1 Pipe MaterialHOBAS Jacking pipe is made of unsaturated polyester resin, silica sand, glass fibre and reinforcing fillermaterials. Through the centrifugal casting process, the raw materials are fed into a rotating mould andthe pipe wall is built up, layer by layer from the outside inwards. Centrifugal acceleration of up to 70 gcauses the layers to be compacted and removes air voids.

Figure 1: HOBAS wall structure

Composition Function

1 Sand encapsulated in resin 1mm thick.

External protective layer

2 Glass fibre, polyester resin Outer reinforced layer

3 Glass fibre, polyester resin, sand Transition layer/Structural

4 Sand, polyester resin, glass fibre Reinforcinglayer/Structural

5 Glass fibre, polyester resin, sand Transition layer/Structural

6 Glass fibre, polyester resin Inner reinforcedlayer/Structural

7 Glass fibre, polyester resin Barrier layer

8 Pure resin 1 mm thick. Inner protective layer

3.1.1 Diameter

HOBAS Jacking pipe is available in diameters from 200 mm to 3000 mm. The focus of this report hasbeen on DN1000 however; in general the findings of this report can apply to various diameters.

3.1.2 Pressure

Sewer pipelines fall into two categories: gravity sewer and rising mains. Both were considered here. Mostsewer jacking pipe is gravity pipe of PN1.

3.1.3 Stiffness

HOBAS Jacking pipe is available in stiffness from SN 32,000 to SN 1,000,000 i.e. 32,000 N/m2 to1,000,000 N/m2.


3.1.4 Length

HOBAS Jacking Pipes are produced in standard lengths of 1, 2, 3 and 6 m but can be made in anycustom length that the application requires from 0.2 up to 6 m.

3.2 JointsThree types of joints are available for HOBAS jacking pipe each with a coupling mounted onto one end ofthe pipe and an elastomeric gasket which seals the pipes. The choice of the different type of joint isdependent on pipe size and project conditions.

3.2.1 GRP Coupling

The GRP coupling is made of glass fibre reinforced polyester resin. Primarily used for larger diameters, itfeatures a sliding seal for leak tightness

3.2.2 FWC Coupling for Pressure Jacking Pipes

The FWC coupling is made of glass fibre reinforced polyester resin with an integral full width EPDMgasket and is fitted to the pipe wall. This coupling is used as standard for the various nominal pressureratings of HOBAS Pressure Pipes. Jacking pipes with this coupling can be operated as pressure pipesright away.


3.2.3 Stainless Steel Coupling

The stainless steel coupling consists of a stainless steel ring with an EPDM seal firmly attached to it. It isused as standard for smaller and medium nominal diameter pipes.


4. Project Requirements

4.1 Design Life DurationSewers are typically required to have a 100 year life.

4.2 Design Life DefinitionDesign life can be defined in different ways and there is no standard definition.

The end of sewer structures service life can be defined to occur when:

Deterioration progresses to a level that makes the structure unsafe or unserviceable.

The level of maintenance necessary to maintain the functionality of the structure becomesuneconomical.

The above service life definition recognises the need for ongoing inspection and maintenance to achievethe design life. In simple terms, the end of design life, i.e. failure in sewer pipes is when leakage occursor burst/structural failure.

AS 1254 states “It should be noted that, by convention, plastics pipe systems are often designed on thebasis of 50 years extrapolated test data. This is established international practice but is not intended toimply the service life of drainage pipes is limited to 50 years. For correctly manufactured and installedsystems, the actual life cannot be predicted, but can logically be expected to be well in excess of 100years before major rehabilitation is required.”

4.3 How Pipelines FailFailure of pipelines can typically be separated into structural failure and leakage. Structural failure occurswhen the loading regimes exceed the structural capability of the asset. For constant loading regimes,degradation or damage of the pipe material resulting in a reduction of the structural integrity of the assetis the dominant factor influencing the expected time to failure. For a structurally sound pipe, a change inthe loading regime due to variations in environment (e.g. ground movement, change in applied loadsabove the pipe, loss of support bedding) is the main factor governing the expected time to failure.

Leakage typically occurs where degradation or damage defects grow to a depth exceeding the wallthickness of the pipe, and the stress concentration associated with this defect is not sufficient to causerupture of the pipe under the loading regime. Leakage at fittings can be caused by degradation of theseal, damage by tree roots or misalignment due to environmental changes.

These factors apply to pipelines of all materials. From a durability approach, achieving the design life isreliant upon providing a constant loading regime of the pipe through correct installation of the pipe(bedding the pipe correctly, allowing for stress relief at joints, etc). Once this is done design life is reliantupon minimising the degradation and damage of the pipe material, both from internal and externalenvironments.


5. Exposure Conditions

This study considered HOBAS jacking pipe for use in sewage applications. Conditions during installation, testing, operation and maintenancehave been considered. Some exposure conditions were taken from Queensland Urban Utilities Water and Sewage Planning Guidelines 2010.

Table 1 Exposure Conditions of Sewage Pipe

CHEMICAL CONDITIONS- Internal

Contents Sewage, pH controlled to 7.0 to 11.0 however, pH down to ~2 possible

Contaminants & Products ofDecomposition

Gaseous Hydrogen Sulphide concentration in sewer headspace 15 ppm (based on the short termexposure limit for occupational exposure). Forms sulphuric acid on contact with bacteria & water.

Other Chemical dosing can occur (e.g. to limit H2S, odour and for pH control). This my include magnesiumhydroxide, oxygen injection or other chemicals

CHEMICAL CONDITIONS -External

Buried in contact with soil, ground water, saline groundwater. Acid sulphate soils in some locations, pH~ 4.5 but can be as low as 2, potential for contaminated soils in others.

THERMAL CONDITIONS - Internal Ambient (23±5)°C (as defined in ISO 10467)

THERMAL CONDITIONS - External Ambient (23±5)°C (as defined in ISO 10467)

PHYSICAL CONDITIONS - Internal

Pressure Gravity, PN1. Pressure is variable, depending on the project. Pressure spikes must be considered.

Vacuum Vacuum sewers are uncommon however, a vacuum can occur e.g. in pressure pipelines due tosudden closure or opening of valves (water hammer), in pipelines with insufficient ventilation, inpipelines with gradients after sudden filling or flushing.

Cyclic conditions. Surgepressures.

Localized surcharging is possible. Water hammer can occur due to sudden closure or opening ofvalves.

Mode of operation. Pipes in continuous operation. Rising mains experience pump starts and stops.


Velocity of the contents Rising Main: Ideal velocity 1.0 – 1.5 m/s, Minimum velocity 0.6 m/s, Maximum velocity 3 m/s. GravityMains also exist

Abrasive qualities of the contents(particle type, size, shape,hardness)

Total Dissolved Salts concentration <1000 mg/L. Consider particles of sewage, dirt, silt etc.

Capacity Gravity Sewer Requirements (Conventional): Maximum sewer capacity (Q manning): Conventional -Sewer flowing full with no surcharge, Nu-Sewer - 70% of the pipe diameter

Maintenance Water jet cleaning may be used (e.g. to remove dirt build up)

PHYSICAL CONDITIONS - External

Installation Jacking loads

Loads Soil, traffic

Supporting method Soil and grout

Other Consider ground movement

RADIATION CONDITIONS -External

Sunlight whilst stringing only

BIOLOGICAL CONDITIONS Bacteria, sulphate reducing bacteria, rodents, fungi, tree roots, insects

ELECTRICAL CONDITIONS Stray electric currents (e.g. chemical reactions or adjacent power lines).


6. Effect of Exposure Conditions on Product

6.1 Chemical EnvironmentThe internal and external chemical environment has been considered including the chemicals at ambienttemperature given in Table 1. Sulphuric acid can occur as a result of acid sulphate soils and in sewagewhen bacteria and water react with hydrogen sulphide. The concentration of sulphuric acid in the sewageand soil environment is weak; a pH of 2 corresponds to a sulphuric acid concentration of 0.1%. Dosingchemicals are also used in sewers, mainly magnesium hydroxide and oxygen injection. Magnesiumhydroxide is a weak base with pH less than 10.

The glass reinforcement, sand and fillers in HOBAS jacking pipe are encapsulated in resin. Thus thechemical resistance of the HOBAS is dependent on the resin. The outside layer contains sandencapsulated in resin with a thickness of at least 1 mm. The inside of HOBAS jacking pipe is made up ofan internal layer of resin with a thickness of at least 1 mm. An internal resin rich layer of a minimumthickness of 0.25 mm is required by AS 2634 to provide corrosion resistance. ISO 10467 requires athermosetting resin layer with or without aggregates and fillers and with or without reinforcement.HOBAS pipe meets these requirements through the provision of an internal layer of pure resin.

There are many types of resins used in composites and the datasheets of the two resins used in theinternal and external layers of HOBAS pipe have been provided. One is described as a “special polyesterresin” whilst the other is a tetrahydrophthalic anhydride and neopentylglycol based unsaturated polyesterresin. Both products fall under the umbrella group of unsaturated polyester resins. These resins are thegeneral purpose resins of the composites industry for use in mild environments. Typically unsaturatedpolyester resins are resistant to attack by weak acids and bases, at the concentrations commonly foundin sewers and in acid sulphate soils.

An analysis of the molecular structure of the resins was conducted as part of this report. Theneopentylglycol component of one of the resins gives slightly higher chemical resistance than othergeneral purpose unsaturated polyester resins. Being unsaturated polyester resins, ester and unsaturatedgroups are present in both resins. These groups can be attacked in strong acids and bases. Suchconcentrated chemicals would not normally be expected in a sewer environment.

Strain corrosion testing of HOBAS has been done in 0.5 mol sulphuric acid (pH ~0.1) and 0.5 molsodium hydroxide (pH 10), at room temperature. Test results show a test sample in the acid forapproximately 12 years and one in the base for over 1 year [HOBAS1]. These conditions are greaterthan those expected in normal sewer operating conditions. These results show a good degree ofresistance to chemical attack.

Experience of the author includes condition assessment of a HOBAS sewer rising main after 16 years inservice. Discoloration of the interior resin only, believed to be due to reaction with the sulphides/sulphuricacid was found. This is common for GRP and is not usually a life limiting factor. Overall the pipe wasfound to be in good condition with no significant chemical attack [GHD1].

Provided the chemical conditions in the sewer and soil are within the normal range (pH 2 to 11) chemicalattack is not expected to limit the design life.


6.2 Long Term Loads (and Effect of Creep)The ring stiffness of GRP pipes reduces over time due to the visco-elastic nature of GRP which causes itto creep under load over time. Ageing can also cause a very gradual breakdown of the material resultingin a change in stiffness. This change in properties has been widely tested and accounted for in design ofthe pipe. The stiffness after 50 years of HOBAS pipe has been measured as 0.3 to 0.6 that of the initialring stiffness [HOBAS1].

Whilst GRP sewer pipe is typically available with stiffness of SN 2500 and above, HOBAS jacking pipe isavailable with stiffness of SN 32,000 and above. The high stiffness of jacking pipe is required towithstand the loads imposed during jacking rather than normal operating loads. Creep under load willresult in reduced stiffness of the HOBAS pipe over time, however as the jacking pipe has started off at ahigher stiffness, it is more resistant to failure.

A number of test methods exist to determine the effects of creep. These subject a water filled section ofpipe to load over extended times and determine the time to failure. Internal hydrostatic pressure is usedfor determining hydrostatic design basis and failure is evidenced by weeping of moisture from the pipe.An external load is used for determining long term ring stiffness and long term ring deflection and failureoccurs when cracks propagate to cause rupture of the pipe wall. Many pipe specimens are tested so thatfailure occurs at times ranging from less than one hour to over 16,000 hours. Results are evaluated usinga log load versus log time regression line of best fit which is projected to obtain future values. The lognature of these results is important, as whilst values at 50 years are commonly reported, values at 100years are not greatly less.

From these tests the strain which results in failure is determined and is shown to decrease with greatertime under load. Strain is used in the design of GRP pipe taking into account the initial properties and thechanges in the strain and stiffness over time.

Table 2 Properties of HOBAS Pipe

Property Value Reference

Short term circumferential strain at break (<PN10 1.2-1.5% [HOBAS1]

Long term circumferential strain at break(<PN10) 0.6 to 0.7% [HOBAS1]

Long term flexural strain at break (after 100years)(DN500, PN10, SN10,000)

1.04% [HOBAS1]

50 year hydrostatic design basis strain (HDB50) 0.62234% [HOBAS3]

In order to gain an understanding of the long term durability of HOBAS jacking pipe, taking into accountcreep a case study examining the strain due to internal pressure was completed as shown below.

Assumptions:

p = Pressure = PN = 1.0 MPa

r = Radius = 1026/2 mm

t = Wall Thickness = 34 mm [HOBAS2, for HOBAS jacking pipe, SN32,000, DN 1026]

Property:


E = Circumferential tensile Modulus = 10,000 MPa [HOBAS1]

Calculations

= Stress = p x r / t = 1.0 x 1026/2 / 34 = 15.1 MPa

= strain = / E = 15.1 / 10,000 = 0.15%

This value of strain, of 0.15% is well below the strain which causes failure after 100 years as given inTable 2. ASTM and AWWA GRP pressure pipe product standard requirements, the maximum allowableinitial ring tensile strain due to operating pressure in the piping system cannot exceed the HDB50 reducedby a 1.8 safety factor. This condition is met using the figures above. Under typical operating loadconditions, failure of HOBAS pipe due to creep is not expected within 100 years.

6.3 Strain CorrosionStrain Corrosion is the combined forces of chemical attack under load over time. This can cause areduction in strain to break of GRP. Standard laboratory testing of pipes by HOBAS has been done in 0.5mol sulphuric acid (pH ~0.1) and 0.5 mol sodium hydroxide (pH 10), at room temperature whilst the testspecimens are under strain. Extrapolation of these results to 100 years has shown a reduction in flexuralstrain at break from a mean value of 2.1% to 0.93% in acidic environments and to 0.89% in alkalineenvironments [HOBAS1]. For comparison the strain corrosion performance of another GRP sewer pipe,Flowtite was researched. Testing in 1 mol (5%, pH 0) sulphuric acid gave a 50 year predicted failurestrain of Flowtite as 0.66% [Flowtite1].

Using the value calculated in section 6.2 of 0.15%, shows that strains due to internal pressure in thesewer environment are well below values at which failure occurs due to strain corrosion and thus straincorrosion is not expected to limit the life of the pipe within 100 years.

6.4 Cyclic or Repeated Load (Fatigue)The fatigue behavior of steel tends to involve intermittent propagation of a single crack whilst the materialclose to the crack is virtually unchanged. In contrast to this, cyclic loading of composites results in theformation of many, micro sized cracks. Since the small cracks in composites are spread uniformly in thematerial rather than concentrated in a single area, a greater area of material is involved in resistingfatigue failure. Furthermore, as the formation of each small crack, absorbs energy, composites tend tohave good fatigue resistance compared to most metals.

6.5 Biological Conditions & Tree RootsBiological conditions in an underground sewer environment include rodents, fungi, insects, tree roots andbacteria. Sulphate reducing bacteria produce sulphuric acid and the durability of HOBAS exposed to acidhas been covered in section 6.1. The resins used in HOBAS pipe are unsaturated polyester resin whichare synthetic petroleum based resins and not typically a food source for rodents, fungi or insects. Theother materials in HOBAS pipe are silica sand, glass fibre and reinforcing filler materials which are notreadily attacked.

Tree roots typically follow the path of water, for which a crack or through wall delamination would havehad to occur in the pipe wall (joints are covered in section 6.11). The wall thickness of SN 32,000, OD1026, PN1 HOBAS pipe at 34 mm is relatively thick in terms of meeting internal pressure and external


load requirements. This wall thickness thus provides good capacity for resisting cracking anddelamination and thus tree root intrusion.

6.6 Abrasion including Water Jet CleaningThe extent of abrasion is dependent on a number of factors listed below and indicative figures are given:

Angle of flow: impingement and turbulent flow causes greater abrasion than parallel flow.

Rate of flow: high velocities increase abrasion. For composite materials, velocities up to 4 m/s tend tobe benign but abrasion occurs above 10 m/s [Mallinson]. The maximum velocity expected duringoperating sewers is 3 m/s.

Concentration of particles in flow: higher concentration causes higher abrasion.

Particle size: larger particles cause more abrasion. Most particles 100 mesh in slurry do not causemuch abrasion whereas particles 6-12 mm diameter can [Mallinson].

Particle hardness: harder particles cause more abrasion. Abrasion can occur in composite pipes withlarge, very hard particles with Mohs hardness of 6-9 [Mallinson]. Nearly all the crystalline salts arerelatively soft, with a Mohs hardness of about 2 and are generally not a problem for abrasion ofcomposites [Mallinson].

Particle shape: angular particles cause greater abrasion than spherical.

Location: abrasion is greater at the bottom of pipes due to heavy particles sinking. Abrasion isgreater at elbows and changes in direction of pipes.

6.6.1 Sewage Flow

Pipes are tested for abrasion using the Darmstadt Rocker test. A test piece of pipe is filled with water andsand or corundum then tilted alternatively so that the abrasive slides from one end of the test piece to theother. The average abrasion wear of pipe samples after 100,000 cycles corresponds to an operationallife time of 50 years according to one source and according to a second source 200,000 cyclescorresponds to 30 years. Laboratory testing by HOBAS of their pipes showed that after 500,000 cycles0.9 mm of wear had occurred [HOBAS1]. A typical result for isophthalic polyester (RPM) pipe under thistype of test is given by Mallinson as wall thickness loss of 1.9 mm after 3 million revolutions [Mallinson].The inner resin layer in HOBAS jacking pipes is at least 1 mm. Based on these tests abrasion by normalsewage flow is not expected to be a limiting factor over a 100 year life.

6.6.2 Water Jet Cleaning

Whilst the smooth surface of HOBAS pipe helps prevent build-up of material, water jet cleaning ofsewers can occur and the effect of this is considered. In a study by Cowlings et al, a solids free jet ofseawater was impinged on composite pipe. At angles of 90° and 45°, and flow of 100 m/s the materialshowed significant erosion damage after 200 hours. Damage was less for an angle of 25°. Note that thisis an extreme test with a very high velocity impinging jet of water. Preliminary experiments carried out byCowlings et al at a lower velocity of 40-60 m/s showed no evidence of abrasion even after 100 hours.[Cowling et al].

Testing by HOBAS has been done to DIN standard 19523, which uses 60 cycles of potable water, at 110bars, a jet power density of 330 W/mm2 and an angle of 30°. No damage of HOBAS pipes was seen and


thus the pipes meets the DIN standard 19523 [GmbH1, GmbH2 and HOBAS4]. Tests have also beenconducted by HOBAS on HOBAS CC-GRP Sewerline® water pipes using water with addition ofgranulated materials (e.g. gravel, sand) to simulate effects of repetitive cleaning over many years. Thetests were performed according to various national and international technical guidelines and standardsat 120 bar pressures. Pipes, joints (HOBAS Sealtight®) and connections (tees, wyes) were exposed tostatic and dynamic water jets simulating up to 100 flushing cycles. The tests showed that the surface andstructure of HOBAS CC-GRP Sewerline® pipe systems for sewage were not adversely affected[HOBAS5].

During cleaning, a high-pressure water hose and a jet nozzle are pulled into the sewer pipe and in theprocess, the hose often moves at high speed. Moreover, the jet nozzle may lift off the base and impactthe pipe. These effects were tested in a German study [GFEF]. HOBAS pipes were found to be“relatively resistant to impacts” [GFEF]. Only nozzle impacts on a house connection caused tears in thelaminate, but these tears were not continuous in form [GFEF].

The experience of the author with composite pipes in the Australian mining industry is that water jetcleaning can cause abrasion and rupture. The nature of a high pressure jet of water is that at very highpressures, at high impingement angles and at low water volume to pressure ratio damage to composite(and to many materials) is possible. Water jet cutting is a common method used in industry. Thus theresistance to water jet cleaning damage of pipes is somewhat reliant on adherence to documentedcleaning practices and the pipe manufacture’s recommendations. However, the testing by HOBAS andby Cowling et al and GFEF show a good degree of resistance to water jet cleaning, particularly at lowangles of impingement. HOBAS has published water jet cleaning instructions for maintenancecontractors and if these practices are reasonably followed, no damage is expected to occur to the pipesystem during water jet cleaning.

6.7 Stray CurrentsStray electric currents can be generated by either chemical reactions or adjacent power lines. These cancorrode metallic pipe systems. The materials in HOBAS pipe (polyester resins, glass, sand, mineralfillers) are non-conductors of electricity; hence the HOBAS pipe is not subject to electrolytic corrosion.

6.8 UV (Sunlight)The HOBAS jacking pipes for buried sewer application are generally only exposed to UV radiation duringthe stringing process and transportation to site. This limited exposure to UV radiation is considered notdetrimental to the long term durability of HOBAS pipes.

6.9 TemperatureThe resistance of composites to temperature is dictated by the heat distortion temperature (HDT) or theglass transition temperature (Tg) of the resin, i.e. the temperature at which the resin softens. The othercomponents of composites (glass, sand, mineral fillers) can typically handle hundreds of degrees and donot limit the temperature resistance of the product. The temperature in a buried sewer environment isrelatively constant (23 ± 5°C).


Table 3 Thermal Properties of Resins in HOBAS Pipe as Given on Technical Datasheets

Resin HDT (°C) Tg (°C) Max Use (°C) Reference

Inner Layer 25 50-75 Lonza Group1

Outer Layer 40 70 Reichhold1

Structural 98 Reichhold2

ISO 10467 requires that the resin used in the structural layer have a temperature of deflection of at least70°C. This is met for HOBAS pipe as shown in Table 3. ISO 10467 also states that the resin used in theinner layer and that for the outer layer need not conform to this temperature of deflection requirement.The resins in HOBAS pipe thus meet the temperature requirements of ISO 10467.

The Tg of 25 °C of the inner layer indicated it is relatively easily deformed at ambient temperatures. Thismay affect other properties such as abrasion resistance. In ambient sewer temperatures degradationdue to temperature alone is not expected.

6.10 Ground MovementHOBAS jacking pipe is supported by soil and in usually also grout. In order to maintain a consistentstress environment all pipes must have solid, uniform and continuous support along the full length of thebarrel. From a durability approach, achieving the design life is reliant upon providing a loading regimethat is as constant as possible by correct installation of the pipe (jacking the pipe correctly, allowing forstress relief at joints, etc).

Ground movement results in a change in the loading regime on the pipe. Depending on the severity ofthe change, as with all pipe materials, the stresses can be sufficient to cause structural failure of the pipeor misalignment and leakage at joints. The minimum stiffness of HOBAS jacking pipe is SN 32,000 asrequired to withstand the loads imposed during jacking. The joints compries a coupling and elastomericgasket which allows for minor movement and thus some stress relief. The joint meets the compliancerequirements of EN 691-1, ISO 8639, EN 1119, and DIN 4060, such that they remain sealed even whendeflected [HOBAS1]. These features give HOBAS reasonable capacity to withstand ground movement.

6.11 JointsJoints are formed by a coupling mounted onto one end the pipe and the elastomeric gasket which sealsthe pipes (see joints types in section 3.2 ). The choice of the different type of joint is dependent on pipesize and project conditions.

Joints are a common point of failure including failure due to and tree root intrusion in all pipelines. Whilstthis remains the case for HOBAS pipes, a couple of aspects of HOBAS jacking pipes reduces theirfailure likelihood. Due to the elastomeric deflection of the HOBAS pipe, timber packing rings are notrequired to alleviate the jacking load. Thus the problems of swelling and subsequent damming, lack ofsealing and misalignment of joints due to the space taken up by the packing ring against the elastomericseal are not a concern with the HOBAS system. Furthermore, the automated manufacturing process andtolerances of HOBAS tends to produce pipes of uniform diameter and wall thickness and thus more


precise joints. Testing of gaskets by HOBAS gave a residual long-term (>50 years) sealing pressure ofmore than 80% [HOBAS1]. These properties make HOBAS jacking pipe joints relatively resistant to leaksat joints.


7. Summary Durability Assessment

Table 4 – Summary Durability Assessment of HOBAS Jacking Pipe in Underground Sewer Environment

Environment DeteriorationMechanism

Protective Measure Review

Chemicalenvironment –sulphuric acid inacid sulphatesoils andinternally,magnesiumhydroxide dosingchemicals, grout.

Chemicaldegradation andbreakdown of theresin and glass.

Resin encapsulated outer layer1 mm. Internal pure resin

layer 1 mm.

Unsaturated polyester resins

This structure meets ISO 10467 and follows the general principal ofa resin rich layer used to resist corrosion.

The resins used are and these are typically resistant to attack in theweak acids and bases found in sewers, soil and grout.

Testing by HOBAS of pipes in acid and alkaline environmentsshowed a good degree of resistance to chemical attack.

Provided the chemical conditions in the sewer and soil are withinthe normal range (pH 2 to 11) chemical attack is not expected tolimit the design life.

Hydrostatic load,external loads.

Creep causing areduction in ringstiffness over time.

High initial pipe stiffness.

Testing of pipe to determinestrain at failure after long termload.

Under typical operating load conditions, failure of HOBAS pipe dueto creep is not expected within 100 years.

Chemicalenvironment +hydrostatic andexternal loads

Strain corrosion High initial pipe stiffness.

Testing of pipe to determinestrain at failure after long termload.

Under typical operating load conditions, failure of HOBAS pipe dueto strain corrosion is not expected within 100 years.




Sewage flow Abrasion/wear Internal pure resin layer 1mm.

HOBAS abrasion testing gave 0.9 mm of wear in 500,000 cycles, ~equivalent to at least 75 years’ service. Independent tests give atypical result for isophthalic polyester (RPM) pipe of 1.9 mm of wearafter 3 million cycles.

Based on these tests abrasion by normal sewage flow is notexpected to be a limiting factor over a 100 year life.

Water jetcleaning

Wear and impactdamage

Internal pure resin layer 1mm.

The nature of a high pressure jet of water is that at very highpressures, at high impingement angles and at low water volume topressure ratio damage to GRP (and to many materials) is possible.Thus the resistance to water jet cleaning damage of pipes issomewhat reliant on adherence to cleaning practices and the pipemanufacture’s recommendations. However, the testing of HOBASpipe show a degree of resistance to water jet cleaning.

Stray electriccurrents

Electrolytic corrosion The materials in HOBAS pipeare polyester resins, glass,sand & mineral fillers.

These materials are non-conductors of electricity hence the HOBASpipe is not subject to due to electrolytic corrosion.

UV/Sunlight Breakdown of resin Pipe underground for most oflife

This limited exposure to UV radiation during stringing and transportis considered not detrimental to the long term durability of HOBASpipes.

Rodents, insects,fungus

Biological attack The materials in HOBAS pipeare polyester resins, glass,sand & mineral fillers.

Biological attack of HOBAS jacking pipe is not expected to be a lifelimiting factor as the materials used in its construction are nottypically a food source or readily attacked.

Heat Thermal breakdownof resin

Sewer environment is ambient. In ambient sewer temperatures degradation due to temperaturealone is not expected.




Cyclic loads Fatigue Many small cracks form inGRP absorbing the load.

HOBAS jacking pipe being a GRP construction is also expected tohave good fatigue resistance.

Groundmovement

Load inducedcracking or structuralfailure

Minimum stiffness of SN32,000. High wall thickness.Joints allow for minormovement and thus somestress relief.

Excessive ground movement can cause failure however; HOBASjacking pipe has reasonable capacity to withstand groundmovement.

Tree rootintrusion

Leakage Absence of timber packingrings. Joint design. High wallthickness.

HOBAS jacking pipe have good resistance to tree root intrusion.

General Joint failure Absence of timber packingrings. Uniform pipe diameterand wall thickness.

HOBAS jacking pipes are relatively resistant to leaks at joints.


8. References

AS 1254 - “PVC-U pipes and fittings for stormwater and surface water applications”, 2010

AS 2634 – “Chemical Plant Equipment Made from Glass-Fibre Reinforced Plastic (GRP) Based onThermosetting Resins”, 1983.

[Cowling et al] - Cowling, M.J, Hodgkiess, T and McInally, A, “Impingement Erosion behaviour of FRPComposites in Marine Environments”, Glascow Marine Technology Centre, University of Glasgow.

[GHD1] GHD Report, Document Number 359678.

[GFEF] - German Federal Environment Foundation, Ref no. 20136, “Analysis of sewer cleaningprocedures using high-pressure water jetting equipment and the formulation of recommendations for theprevention of drainage systems damage”, Berlin, 2004.

[GmbH1] – GmbH Oldenburg, “Certificate of jetting resistance according to DIN-standard 19523”,HOBAS pipe, 2008.

[GmbH2] – GmbH Oldenburg, “Certificate of jetting resistance according to DIN-standard 19523”,HOBAS pipe, 2008.

[Flowtite1] – Pearson, L.E, Flowtite Test Report, “Strain corrosion Performance”, Flowtite Pipe –FP2.0,Report Number T-99-107, 1999.

[HOBAS1] - Features Tests and Benefits

[HOBAS2] – HOBAS® Technical Product Data, Gravity Pipe Systems, HOBAS Engineering GMbH,2011.

[HOBAS3] – HOBAS, Product Profile, “HOBAS Pressure Pipes, - ASTM Test Proven for Long-Life”.

[HOBAS4] – HOBAS MResearch Development, Engineering, SGA, Report BE-015_10, BE1.9Labor,“High Pressure Water Jet Cleaning of HOBAS CC-GRP Pipes According to DIN 19523”, 2010.

[HOBAS5] – HOBAS, “Water Jet Cleaning” HOBAS Pipeline Textbook, Section 5.12, 2004.

ISO 10467 – Plastic Piping Systems for Pressure and Non-Pressure Drainage and Sewerage – GlassReinforced thermosetting plastics (GRP) systems based on unsaturated polyester (UP) Resin, 2004.

[Lonza Group1] Technical Datasheet, Lonza Group, 2000.

[Mallinson] – Mallinson,J.H “Corrosion Resistant Plastic Composites in Chemical Plant Design”, MarcelDekker, Inc, New York. 1988

[Reichhold1] Technical Datasheet Reichhold, Product Bulletin, 2005.

[Reichhold2] Technical Datasheet Reichhold, Product Bulletin, 2004.

Documents

Global Pipe Australia Pty Ltd - HOBAS GRP Pipe Systems · Global Pipe Australia Pty Ltd has requested that GHD Pty Ltd prepare a ... thickness of the pipe, and the stress concentration