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RESEARCH IN THE AUSTRALIAN PIPELINE INDUSTRY

MAX J. KIMBERM.J. Kimber Consultants Pty. Ltd.

Chairman, Research & Standards Committee, Australian Pipeline Industry Association

INTRODUCTION

The Australian gas pipeline industry began in 1969 using capital and technology from the UnitedStates of America. Subsequently, state and federal governments became the dominant ownersand operators of most of the long distance gas pipelines, and the Australian industry adapted anddeveloped its own technology to suit its environment. In 1994 the industry entered another, andvery significant chapter in its development, in which pipeline ownership began to revert toprivate companies, new pipeline access regulations were implemented by state and federalgovernments, and new technology was developed to ensure that long distance pipelines could bebuilt economically to serve relatively small markets. This new era of regulation and theprivatisation of government owned pipelines has encouraged U.S. and Canadian energycompanies to return to Australia to look for investment opportunities and to share in Australiandeveloped technology.

Since 1994, more than $A2 billion was committed to new pipeline construction and morethan $A3.5 billion was spent on the acquisition of government owned pipelines, predominantlyby North American companies. This transfer of ownership from the public to the private sector,together with a major review of Australia’s competition policies, forced the federal and stategovernments to make major changes to the regulatory environment. In parallel with this, thecommunity demanded tougher environmental and native title legislation, which has forced theindustry to comply with an increasingly complex set of rules for the construction and operationof pipelines.

In response to these community and economic drivers, the pipeline industry in Australia hasembarked upon a program of research to develop innovative technology to reduce costs andimprove safety and reliability of pipelines that are generally unique to Australian conditions,where markets are small, large distances separate gas sources and customers, and wherefoundation shippers represent only a small portion of a pipeline’s installed capacity. For a mapof Australia’s major gas transmission pipelines, see Figure 1.

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As a result, most new Australian pipelines and many existing pipelines are made from highstrength steel (generally X-70, but X-80 is being seriously considered), manufactured by theERW process, operate at high pressures (15 MPa or 2175 psi) and generally have diameters lessthan 508 mm (20”) (See Figure 12). These small diameter, thin wall, high strength pipelineshave unique characteristics that set them apart from those traditionally built in Europe and NorthAmerica. Therefore, aspects such as fracture control, girth welding, non-destructive testing,third party damage and in-service welding are not addressed in detail in international researchand standards, and need to be investigated thoroughly to ensure that Australian pipelines are atleast as competitive and as safe as those in Europe and North America.

Figure 1 Australia’s major gas transmission pipelines and producing basins

THE DEVELOPMENT OF A UNIQUE PIPELINE RESEARCH PROGRAM

The unique Australian pipeline research program began in 1996, at the initiative of Mr LeighFletcher, the then newly appointed Executive Director of the Co-operative Research Centre for

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Welded Structures (CRC-WS) associated with the Universities of Wollongong, Sydney,Adelaide and Western Australia, the Australian Nuclear Science and Technology Organisation(ANSTO) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) anda number of large industrial corporations with a genuine interest in developing weldingtechnology and advanced research into steel making, steel products, petroleum pipelines andassociated industries. I referred to that program in a paper1 presented to the PRC 9th Symposiumon Line Pipe in Houston in October 1996.

These research programs are managed by a group of industry advisers who have had a great dealof practical experience in all fields of pipeline engineering, many of whom continue to havestrong links with researchers and sponsors associated with PRCI and EPRG research programs.

Since 1996, pipeline owners, operators, contractors and suppliers have sponsored the researcheither directly through the CRC-WS or more recently through APIA. I have had the role ofChairman of the research Program Management Committee since the program began. TheCommittee has been able to secure about $A300,000 a year from industry sponsors. By meansof a multiplier through the CRC-WS, government funding and industry “in-kind” support, we areable to support an on-going research program with a value of about $A1 million per year.

The government funding does not carry with it any obligation to provide the government orregulators with the results of the research, which are held confidential to the sponsors. For thereasons stated above, we have concentrated on thin wall, small diameter high strength pipe. Inaddition, we carry out operational research related to third party damage, coatings andconstruction processes.

The first program of pipeline research in 1996 – 1998 included:

• Non destructive examination of girth welds• Investigation of field welding limits for girth welding thin walled high strength pipes• Determination of defect acceptance criteria for high strength, thin walled pipe• Establishment of crack free welding procedures• Welding on thin walled in-service pipelines• Establishment of automatic girth welding procedures for small diameter thin walled pipe

Since that time, two more two-year research programs have been implemented. In 1998 – 2000,the program included:

• Finite element analysis of welding on in-service pipelines• Evaluation of the use of ultrasonic testing of girth welds in thin wall pipe• Further work on girth welding equipment for small diameter pipe• Cracking in high strength cellulosic welds• Girth weld defect acceptance criteria• Fracture risk in thin wall high strength pipelines• Development of heat flow modelling for application to hydrostatic testing• Resistance to external interference• Review of mechanical jointing techniques

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• Development of a realistic specification for pipeline backfill• Pipeline awareness – development of improved methods of protecting pipelines from third

party damage• Development of standard approaches to technical audits by regulators

The most recent program, that began in late 2000 includes:

• Pipeline resistance to external interference• Pipeline awareness – further development of improved methods of protecting pipelines from

third party damage• Mechanised in-service welding• Development of a knowledge base for mechanised girth welding• Development of on-line monitoring for welding• Hot cracking of weld metal in girth welds• Defect acceptance levels and fracture risk in pipeline girth welds• Adhesion of field joint coatings to extruded polyethylene• Pipeline hydrostatic test behaviour to accommodate 80% SMYS operating stress levels• Investigation into the causes of the precipitation of elemental sulphur in transmission

pipelines

The following is a brief overview of the highlights of the five years of research work, much ofwhich is complementary to the research carried out under the auspices of PRCI and EPRG. Ihope that, if suitable arrangements can be made to maintain confidentiality, there will be anopportunity for results and reports to be exchanged between the three groups.

HIGHLIGHTS OF RESULTS OF THE AUSTRALIAN RESEARCH PROGRAM FROM1996 TO 2000

Investigation of Field Welding Limits for Girth Welding Thin Walled High Strength Pipes2

Investigations were targeted at establishing the practical limits for girth welding of thin-walled,small diameter, high strength linepipe as a function of welding conditions, lifting and lowering-off.

Construction specifications for the welding of cross-country pipelines have historically beenbased on international practice for the laying of relatively thick-walled, large diameter, mediumstrength steel pipe. These specifications almost invariably require 100% completion of the rootpass, and in some cases also completion of the hot pass, prior to release of the internal line-upclamp.

Australian experience with a major pipeline project built with 457 mm (18”) diameter, X70 pipeshowed that relaxation of conventional practice to allow early clamp release and lifting yieldedexcellent results in terms of pipe laying rate and construction efficiency, without any problemsarising with respect to joint quality.

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The investigations revealed that the expansion and contraction occurring in and around the girthjoints of pipelines are strongly influenced by the restraint applied by the use of wedges and bypre-placed weld metal. The last weld metal to be placed in making the root pass is subjected tothe highest restraint, and all of the solidification shrinkage and contraction which occurs duringcooling from the solidification temperature must be absorbed by the weld metal itself. Earlyrelease of the internal line-up clamp, and early lift and lowering while root pass welding is beingcompleted allows stresses and strains to be accommodated, reducing the residual stress whichmay have an adverse effect on HACC (hydrogen assisted cold cracking) on cooling. The “hotstrength” and “hot ductility” of the E6010 weld metal allow for the absorption of thethermally-induced strains and externally applied strains without cracking.

The judicious placement of root pass weld metal at the top and bottom chords enables themaximisation of the section modulus of the partially completed weld and ensures that thepartially welded pipe joint does not behave as a "hinge" during lifting and lowering-off. Evenwith only 50% of the root pass weld metal deliberately placed at the side chords, hinging duringlifting and lowering-off did not initiate cracking.

Welding trials using X60, X70 and X80 pipe in diameters ranging from 219 mm (8”) to 457 mm(18”) and welded with E6010 electrodes, revealed no cracking in root passes in welded pipehaving only 50% root pass completion prior to release of the internal clamp and lifting. It ispostulated that lifting while the newly deposited E6010 weld metal at the bottom chord positionis still at elevated temperature takes advantage of the "hot strength" and "hot ductility" of theweld metal in terms of the ability of the metal to absorb tensile strains induced by contractionand lifting and more so being well above HACC temperature. Plastic straining of the weld metaland the heat affected pipe material has been shown to occur, the magnitude of the strains beingdependent on the level of restraint and the severity of the lift. Importantly, on lowering-off, therelaxation of these tensile strains results in a reduction of the final residual stress state at thebottom region of the pipe.

It would seem that the current industry practice of restricting productivity by specifying theline-up clamp not be released until 100% of the root pass is welded is an unnecessary restrictionfor small diameter pipelines.

On the basis of this work, no barrier exists to allowing clamp release after 50% completion of theroot pass when using E6010 electrodes for making the root pass.

This project was found to be a great value to the pipeline industry and was implemented duringthe construction of the Mt. Isa to Ballera pipeline (841 km), where a 70% or less of the root passwas completed prior to clamp release for welding of 323 mm (12”) X70 pipe. This allowedpipeline construction to proceed at an average of 500 welds per day or 8 km per day – indeed, onone day 11 km of pipeline was welded, ditched, lowered in and back-filled.

In addition to both the experimental and field work on a construction spread, that was describedabove, finite element, thermo-plastic models have been used to study the development of stresseswithin a typical pipeline girth root weld during line-up clamping, welding and lifting andlowering. By producing models to simulate the stress pattern during the construction process,

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the process may be altered in order to reduce the risk of cracking and increase the forward paceof construction.

Past work has separately calculated both lifting stresses and residual stresses during pipelineconstruction by using beam-theory, or 2D axi-symmetric models. Full 3D models of thecomplete process including line-up clamping, lifting and lowering and the evolution of residualstresses within the root weld and in the subsequent capping pass have not been attempted.

A significant computational problem with such models is the need to rationalize tworequirements. The need for a fine mesh in the weld zone (order of mm) to appropriatelydetermine the local geometry and the stress there, and the need to minimize the mesh used tomodel a large structure (of the order of metres).

Full 3D non-linear, elasto-plastic pipe models of the lifting process were initially created. Theseresults were produced with relative computational ease considering a mesh of three pipe lengths(30-40 metres) was used. Internal pressure from the line-up clamp places an additional load onthe pipe, which was also simulated. A moving line-up clamp has a significant effect on thebending stress placed on the pipe, since it is similar in weight to that of an additional length ofpipe.

However, to model accurately the construction process, the lifting model had to be incorporatedinto a thermal and residual stress model. These transient thermal and stress models require thatshort time steps be used in order to achieve convergence. Due to the computational intensityrequired it was not feasible to use a full pipe mesh. A sub-modelling strategy was developed toovercome this problem. The forces from line-up clamping and lifting and lowering were foundby firstly solving a full pipe model, and then used as a transient loading pattern on a sub-modelof the near weld region. Numerical tests established that these sub-model forces produce thesame stress results on the sub-model as those that were calculated using a full pipe model.

Transient thermal models of the welding of the root pass were produced considering two welderswelding the root pass at the same time. In order to reduce solution time to an acceptable levelthe temperature verses time data from the thermal model was interpolated onto a coarser meshfor use in the residual stress calculations. The forces that were calculated from the liftingprocess were included in the residual stress model, as transient boundary conditions.

This process has resulted in a full 3D transient analysis of the construction process indicating thefull stress history of the root pass during construction. Work is currently underway to evaluatethe effects of process variables on this stress cycle. These variables include welding heat input,the percentage of completed girth weld before lifting, the timing of lifting after welding, the liftheight and the pipe geometry.

Establishment of Automatic Girth Welding Procedures for Small Diameter Thin WalledPipe3,4

Girth welding of a pipeline in the field represents a significant proportion of the installation costand is currently performed by highly skilled manual welders using the shielded metal arc process

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(SMAW), cellulosic electrodes and a ‘stovepipe’ technique. The use of lower wall thickness hasthe potential to reduce the number of weld runs and the overall cost. The higher yield strengthlow alloy pipe materials have been shown to have excellent weldability but as yield strengthincreases there may be an increased risk of weld metal cracking, particularly if overmatchingwelds are required.

This project evaluated the current field welding practice and assessed the feasibility ofmechanising the girth welding operation to achieve lower installation costs and improvedoperating tolerance for higher yield strength steels. The project was considered important to theAustralian pipeline industry, since a world-wide search in 1997/98 revealed no automaticwelding machines suitable for small diameter pipeline construction over long distances at highbuild rates (up to 10 km per day).

It was decided that GMAW (using new technology controlled transfer) would be used as thebasis for the development of a mechanised welding process. During 1998/2000, a girth weldingmachine was developed and tested. The machine is shown in Figure 2.

Figure 2 Girth welding machine

During the course of developing single sided welding procedures for GMAW it was decided toinvestigate the possibility of on line monitoring of weld quality. The feasibility of through arcmonitoring has been demonstrated in similar mechanised welding applications5 and in the case ofpipeline girth welding it offers the potential to identify the probability of defects and target NDE.

A portable monitoring system was built and used to monitor and record electrical parameters(current, voltage, wire feed rate, gas flow, and position). The system is shown in Figure 3

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Figure 3 Portable monitoring system for GMAW girth welding.

It comprises a standard laptop computer with a PC card analogue to digital converter (ADC),signal conditioning unit and appropriate sensors. The sample rate chosen may be varied but isnormally around 5000 to 10000 samples per second. The raw data files were used for the initialdefect identification trials but it was found that for practical purposes the data could becompressed by extracting significant statistical values and storing these at a rate of 4Hz.

Initially an integrated software package was written in LabWindows to perform the dataacquisition and analysis functions. Using a prototype mechanised girth welding system and aproprietary tractor, an extensive range of experiments was conducted to simulate the extremes ofwelding parameter envelopes for pipeline girth welds6.

From this work a series of algorithms which relate common imperfections to on-line electricalsignals were developed. In particular, risk of lack of fusion, burn through, porosity and processinstability can be identified as well as deviations from predetermined process parameters.Algorithms for contact tip to work piece distance (CTWD) have also been developed and theapplication of these to torch height control is currently being investigated using the prototypewelding head.

The monitoring system has been further developed to simplify the user interface and allowremote programming and reporting via the internet. The data acquisition system is incorporatedin a server which would typically be located on the front end side boom tractor/truck. Voltage,current wire feed speed, GPS and travel speed sensors are attached to appropriate points onwelding system and hardwired back to the signal conditioning and ADC unit. Additional dataentry may be relayed from a ‘Palm’ type device equipped with a bar code reader via a wirelesssystem back to the server. The server communicates to a repeater or local client via a wirelessnetwork on site and to remote clients via satellite, WAP telephone link and/or a hard wired

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broadband system. Access to the system is granted at four levels each of which is passwordprotected.

The welding procedure specification (WPS) database may be stored on a remote client computerand individual procedures may be downloaded to site. The procedure can be physically linked tothe power source and welding head controller to automatically preset welding parameters. It alsoembodies the tolerance limits which are used for statistical process control and trend analysis.

During welding the local server screen displays only a progress indicator and defect alarms buton completion of the weld the data is stored locally and available for interrogation by connectedclients. The main reporting screen shows an analogue of the pipe with successive weld runsindicated by concentric circles. The potential ‘imperfections’ are indicated by colour coding asshown in Figure 4. The data may be further interrogated for trend analysis and defect diagnosis.

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Figure 4 Typical display on weld monitor

The system has been assembled for laboratory trials and has been demonstrated to the AustralianPipeline Industry Association. Tolerant one sided welding procedures have been developed forX80 pipe using the prototype welding head and appropriate power sources. Current work isfocussed on further testing and a design review of the system prior to field trials in mid 2001.The computer controlled mechanised GMAW girth welding system developed in the course ofthe work is being maintained as a test bed for further monitoring and weld integrity trials, but itis intended to progress the development and commercialisation of the monitoring systemthrough suppliers of commercial girth welding systems. It is interesting to note that the originalportable monitoring system has been used in the field for surveillance of in service weldingprocedures and has generated very useful data even though the manual metal arc process wasused.

Determination of Defect Acceptance Criteria for High Strength, Thin Walled Pipe7

The Australian pipeline industry through the Australian Standard for Gas and Liquid PetroleumPipelines, AS2885.2, has adopted a 3 tier approach to assessment of girth weld defects. Tier 1 isa workmanship level which (depending on pipe diameter & wall thickness) contains considerable

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conservatism. Tier 2 is a generalised fitness for purpose (FFP) based level, and Tier 3 allows foran Engineering Critical Assessment (ECA). This approach, which is heavily based on theEuropean Pipeline Research Group (EPRG) guidelines, has serious limitations in terms of wallthickness range, 7 - 25 mm, and also pipe grade, maximum X65 in the case of Tier 2. InAustralia, pipe wall thickness is often less than 7 mm while X70 grade is commonplace withX80 at the small tonnage trial project stage.

This research project was undertaken to assess girth weld workmanship defect acceptance limitsin the thin walled, high strength linepipe for the Australian pipeline industry.

Previous work has demonstrated that the requirements of the Australian Standard AS2885.28

Tier 2, which is currently limited to X65 grade pipe in a wall thickness range 7 - 25 mm can infact be extended to include X80 grade pipe and a wall thickness down to 5 mm, provided weldmetal yield strength overmatching is assured. This was an important extension for the Australianpipeline industry but unfortunately it precluded the continued use of the traditional manualcellulosic welding process. This was primarily due to the strength limitation of theseconsumables. The work also demonstrated that the level of strength matching required wasdependent on wall thickness because as the wall thickness increased the proportion of theassumed defect depth diminishes.

With this increased understanding, the industry requested that the suitability of cellulosicconsumables to meet workmanship defect limits in thin walled (5mm thick) X80 grade pipewelded be evaluated. The approach was to assess maximum allowable workmanship surfacebreaking and embedded defects in girth welds produced using two different cellulosicconsumable combinations, using both wide plate9 and full-scale tension tests (see Figure 5 andFigure 6). Detailed mechanical property assessment of the girth welds was also conducted.

The work has demonstrated that 5 mm thick X80 grade pipe at top of the expected productionstrength range welded with either E6010/E9010 or entirely E9010 failed to meet workmanshiprequirements if it is assumed that the load case condition is displacement controlled loading.More importantly, it was shown that both consumables undermatched the strength of the pipeand that currently permitted embedded defects limits for a pipe wall thickness of 5 mm, inAS2885.2, would not ensure pipeline integrity under this adverse loading. It was also shown byassessment of fracture mode that the required level of weld metal toughness in high strength pipegirth welds may be somewhat higher than that currently specified in AS2885 where yieldstrength undermatching is encountered.

Moreover it was revealed that the level of undermatching recorded in this program could verywell be typical of the normal industry practice of E6010/E8010 welding of X70 grade pipe. Onthe basis of this information another project has been initiated to investigate critical defect limitsfor embedded defects in both X70 grade and also X80 grade in wall thickness range of 5 to 7mm.

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50mm50mm

pipe withtest weld

ram

supportframe

end plate

applied force

Figure 5 Full scale pipe tension test rig Figure 6 Full scale pipe tension test rig

It has been shown that the girth weld defect depth assumption (in AS2885) based on 3 mm weldpass depth cannot be reduced. The results of previous work and plans for the future aresummarised in Figure 7:

Figure 7 Results of wide plate and full scale tension testsNote: WPT=wide plate test, FST=full scale pipe tension test

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Finite Element Analysis of Welding on In-Service Pipelines10

The process of welding onto a ‘live’ high-pressure pipe is frequently employed for the repair,modification or extension of gas pipelines. This ‘in-service welding’ has significant economicadvantages for the gas transmission and gas distribution industries, since it avoids the costs ofdisrupting pipeline operation, and it maintains continuity of supply to customers. In Australia,there is a significant trend towards the use of thin, high-yield-strength steels for pipelineconstruction and there are already high pressure transmission pipelines with wall thicknesses aslow as 3mm. In-service welding is made much more difficult with such thin-walled pipes sincealthough thin pipe walls are more easily cooled by flowing gas, they greatly increase the risk ofburn-through during welding.

In 1996 a survey of the Australian pipeline industry established that there was considered to besubstantial conservatism within the in-service welding procedures currently used. Proceduresgenerally involved a reduction of pressure and gas flow before welding, and were often restrictedto thick walled pipes. In recognition of the differences between the expected Australianrequirements and those previously researched, namely,

• reduced pipe wall thickness (< 5mm),• increased usage of higher strength steels,• lack of quantified information on burn-through limits for thin walled pipes,

the CRC-WS initiated a research project with the aim of establishing technology to support thesafe and effective welding of thin-walled high-strength pipelines. An important feature of theproject was the extensive development of finite element simulations of in-service welding. Thesenumerical simulations covered both 2D and 3D models but, unlike the majority of previousresearch, they sought to develop numerical simulations of burn-through.

Utilising commercial finite element software, a wide range of 2D and 3D models of in-servicewelds have been developed. The capacity to generate stable, accurate models of all in-servicejoint forms has been demonstrated.

To represent the heat loss due to the flowing gas the numerical models follow the Battelle 2Dmodel and utilise the Sieder & Tate non-dimensional approach. This determines an effectiveheat transfer coefficient at the pipe wall, based on the pipe diameter, gas pressure, and flowspeed. By incorporating empirical data describing weld bead volume and joint form, therepresentation of the welding heat input has been tailored for both vertical-up and vertical-downwelding with low-hydrogen electrodes. For circumferential fillet welds, predictions of both t8/5

cooling times and weld penetrations have been made with acceptable accuracy.

The types of in-service welding processes that have been modelled are shown in Figure 8

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(a) “Circumferential Fillet Weld” (b) “Saddle Groove Weld”Figure 8 Types of In-service welds modelled by FEA

Model development has concentrated on a 3D quasi-steady-state analysis of circumferential filletwelds. In practice, this is the most popular joint form. It also provides a numerical analysiswhich allows an acceptably short CPU time. Pre-processing software has been produced toefficiently construct and mesh models of varied geometry. Post-processing software has beenestablished to calculate the distribution of t8/5 cooling times throughout the weld zone. This canbe further used to calculate a distribution of hardness based on an empirical relationship withcomposition and t8/5. Isotherms give an estimate of weld penetration and size and extent of theHAZ. Figure 9 and Figure 10 show the welding and cooling processes for a typical fillet weld.Models have mainly considered single root pass welds but some multi-pass welds and weldrepair sequences have been simulated.

Figure 9: A typical thermal field, for a 95 Amp, 22 Volt, circumferential fillet weld made at 2.3mm/second. The 273 mm diameter pipe of 4.88 mm wall thickness contains methane at 4.14

MPa pressure and a flow velocity of 6.3 m/second.

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Figure 10 The t8/5 cooling times extracted from the thermal field shown in above figure andplotted as a contour map on a section through the mesh

Various methods of assessing the risk of burn-through have been developed. These were basedon:

• the maximum temperature at the inside surface of the pipe, following Battelle,• a thermo-elastic plastic stress analysis,• using the thermal field in the pipe wall to calculate the reduction in wall strength.

Thermo-elastic-plastic models of circumferential welds have showed similar deformationpatterns to those observed during burn-through, namely a localised bulge in the pipe wall nearthe weld. Failure can be specified as a bulge that exceeds a limiting height. Plots of internalpressure versus bulge height have shown an effective yield pressure, which can also be used as afailure index. Only a limited numbers of these models were studied because they were verycomputationally demanding.

For example, a temperature distribution from the pipe-wall to the weld bead surface can be seenin Figure 11 along the line A-A. The local yield stress at the elevated temperatures can then becalculated along line A-A, thereby creating a yield stress distribution along the line. Thismaterial strength is then represented by replacing the line with a new line of thickness teff, whichhas a constant distribution of yield stress for a material at ambient temperature.

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Figure 11 Weld temperature profile

Estimating the reduction in pipe wall strength in the weld zone has created a novel alternativemethod of assessing burn-through risk. This method determines the reduction in materialstrength around the weld, based on the predicted temperature field and the known relationshipbetween material yield strength and temperature. This reduced strength is regarded as equivalentto a local reduction in the thickness of the pipe-wall at constant ambient temperature. Hence, thetemperature field around the in-service weld effectively converts to a ‘cavity’ in the pipe wall. Anumber of alternate strategies can be considered. The limiting pressure for safe welding can bebased on the remaining wall thickness, or based on the effective reduction in cross-sectional area.

The risk of burn-through is equivalent to the possibility of this ‘cavity’ causing rupture at thecurrent operating pressure. This assessment can also be easily carried out utilizing the approachspecified for the evaluation of corrosion cavities in Australian Standard AS2885. This methodhas produced excellent results. Although limited by lack of data, comparison between predictedsafe welding pressures and published values measured on 5 mm thick pipes has been good. Theapproach provided a way of assessing burn-through potential that is in agreement with reportedbehaviour. Longitudinal welds are more prone to burn-through than circumferential ones of thesame heat input. Pressure has a significant effect. The width or size of the weld is important aswell as penetration. It provides an efficient approach to in-service weld simulation since it doesnot require a stress analysis and uses only thermal predictions. Unlike Battelle’s maximum walltemperature approach, it is more realistic since it accounts for weld orientation and internal pipepressure.

Development of Heat Flow Modelling for Application to Hydrostatic Leak Testing11

A study of the thermal behaviour of gas pipelines during filling and pressurisation has beenundertaken. A two dimensional finite difference model was developed to determine thelongitudinal variations in temperature of a gas pipeline when filled with water at a differentinitial temperature to the pipe and to the soil. The results o this modelling are a series of chartsthat show the temperature stabilisation behaviour. These charts can be directly used to assess theoptimum time to commence hydrostatic leak testing under a range of different starting

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conditions. A non-dimensional temperature parameter has been developed to enable results to beapplied to any combination of starting temperatures.

To further understand the behaviour of the buried pipe during leak testing a two dimensionalfinite element model was developed to determine the cross sectional variations in temperaturebetween the water, pipe and soil under a variety of conditions typical of Australian pipelines.Thermal behaviour was modelled for up to 7 days duration for a range of pipe size and soil types.The strong influence of soil properties and pipe diameter was evident. Additionally, the effect ofdiurnal changes was modelled and showed a small but significant effect that needs to be takeninto account during field testing. Soil temperature data has been compiled from a variety ofsources that will provide a valuable reference for future testing exercises. Knowledge of thelikely seasonal and diurnal changes in soil temperature is valuable information that can be usedto reduce the levels of uncertainty in estimating the magnitude of any leaks present.

A review of the gas leakage model from AS1978 has been performed and recommendations forchanges to the standard made. In addition, the charts contained in the standard have beenextended to cover a wider range of leak situations.

Pipeline Awareness – Development of Improved Procedural Methods of ProtectingPipelines from Third Party Damage12

Until recently, the Australian Standard – Pipelines Gas & Liquid Petroleum AS2885 - 1987adopted a prescriptive approach to design against external interference. Pipe wall thickness,stress levels and depth of burial were dependant on the nature of the land use adjacent to thepipeline route – the concept of “class locations” in a manner similar to North American codes.At vulnerable locations such as road crossings, special requirements were specified. Signposting and patrolling were mandated. Pipeline operators were required to keep the generalpublic informed of the presence of the pipeline, and to establish liaison with authoritiesresponsible for excavation, ditch cleaning, road grading, dredging, and other operations that hadpotential to damage the pipeline. Where these requirements were complied with, the pipelinewas “deemed to be protected from third party damage”.

The current revision of the Australian Standard, AS2885.1 -1997, adopts a risk based approachto protection of pipelines from damage. The Standard requires that “each threat to the pipelineand each risk from loss of integrity of a pipeline is systematically identified and evaluated”, andthat “action to reduce threats, and risks from loss of integrity, is implemented so that risks arereduced to As Low As Reasonably Practical (ALARP)”. As threats to the pipeline, and theconsequences of loss of pipeline integrity, change over time, this process is not limited to thedesign stage, but is required to continue over the life of the pipeline.

For protection against external interference, the Standard requires the implementation of physicaland procedural measures. The minimum number of such measures depends on the land useadjacent to the pipeline. To be counted for compliance with these requirements, the measuresadopted must be effective against the identified threats. AS2885.1-1997 specifies minimumstandards for items such as depth of burial and spacing of signs. Compliance with theseminimum standards may provide effective protection, but is not deemed automatically to do so.

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The success of the procedural measures is heavily dependent on the attitudes and behaviour ofthe general public and those involved in excavation work. Information about how the variousprocedural measures interact with these attitudes, and therefore on how they affect pipelinesafety performance, is not readily available to pipeline designers and operators. Consequently itis difficult for them to select an appropriate package of measures for a particular pipeline.

The initial work on this project came to the following conclusions:

(a) In the USA, excavation damage accounts for a little less than half of all pipeline accidents,and about the same proportion of the fatalities, injuries, and damage to property caused bythose accidents.

(b) The main causes of excavation damage are failure to have the facilities located and markedbefore commencing excavation, inaccurate location and marking, and using mechanicalequipment too close to an accurately marked facility.

(c) It is not true that almost all excavation damage is a direct result of excavator negligence orignorance.

(d) Contrary to expectation, there is quite a lot of information available, from public sources, onprocedural measures for avoiding external interference damage to pipelines, and theireffectiveness.

(e) Procedural measures can never be 100% effective, as they are always susceptible to humanfailure, whether intended, or unintentional. Simultaneous use of two or more independentprocedural measures reduces the probability of failure dramatically and, in combination withat least one physical measure, can provide a very high level of protection against excavationdamage. In these conclusions the use of the word “effective”, in respect of particular damageprevention measures, does not imply certainty, but merely a reasonably high probability, ofsuccess.

(f) All the procedural measures found in the literature fall within the general categoriesdescribed in AS2885.1 - 199713, and AS2885.3 - 199714 . There is no need to expand the listof measures permitted by the Standards.

(g) In the USA and Canada, use of the one-call system is regarded as the key to damageprevention. However, around half of all accidents occur despite the one-call service havingbeen used.

(h) Drawings should only be used as a guide to the location of important, or potentiallydangerous, buried facilities. The exact location should be verified by other means.

(i) The procedures for excavating near buried pipelines, given in AS2885.3 – 199714, are sound,and superior to those apparently in use in the USA. However they can only be effective if theexcavators know about them.

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(j) Public awareness programs can be very effective. They need to be tailored to suit thevarious target groups, such as the general public, landowners and occupiers along thepipeline route, excavation contractors, planning authorities etc. They need to employ avariety of methods to ensure the message reaches a high proportion of the target audience.

(k) Utility bill inserts appear to be an effective means of raising awareness among the generalpublic.

(l) The Dig Safely program, in the USA, is a good model of an effective awareness campaign,and could be adapted to suit Australian conditions.

(m) It is unlikely that a single pipeline operator can conduct the most effective awarenessprogram. It is better to have an industry wide approach, probably in conjunction with otherindustries that operate buried facilities, and possibly involving government.

(n) The landowner liaison and third party awareness provisions of AS2885.1 – 199713, andAS2885.3 –199713, need improvements, such as more consistent terminology, and greaterclarity as to what constitutes a conforming awareness program.

(o) Signs are an effective method of ensuring potential excavators are aware of the presence of aburied pipeline, particularly if they are located at every crossing and change of direction, andat intervals in between. Signs, combined with buried marker tape, have an extremely lowprobability of not being noticed.

(p) The provisions of AS2885.1 – 199713, concerning signposting and buried marker tape, areappropriate.

(q) Patrolling is only effective in detecting unauthorised excavation work on or near a pipeline ifit is carried out very frequently, for example daily.

(r) The conditions under which patrolling may be counted, for conformance with the externalinterference requirements of AS2885.1 – 199713, should be tightened. The patrol frequencyneeds to be chosen to be effective against the particular threat it is intended to protectagainst, or minimum patrol frequencies, possibly related to location class, need to bespecified.

(s) There already exists, in Australia, quite a lot of legislation that could be used, moreeffectively than it now is, to encourage safe excavation practices. The existing legislation isof a general nature requiring, for example, employers and others to have safe workingmethods. In most cases, excavation damage to buried facilities is not specifically mentioned.In most cases penalties are unlikely to be applied until after an accident has occurred.

(t) Legislation specifically addressing damage to buried facilities, providing incentives for goodpractices, and penalties for non-compliance, could prove effective in further reducing theincidence of excavation damage to pipelines. There are numerous examples of legislation ofthis type available to use as models.

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Pipeline Resistance to External Interference15

For onshore, buried pipelines built to AS2885-1997, external interference threats and risks areidentified and reduced to As Low As Reasonably Practical (ALARP) by means of a riskassessment process. Resistance to penetration is specified as an External Interference ProtectionMeasure containing two methods: wall thickness and barrier to penetration. Currently, themeans of specifying wall thickness for resistance to penetration relies totally on eitherexperimentation or experience. The principal objective of this report is to provide pipelinedesigners with a common basis for analysing external interference, with particular reference tothose identified threats where resistance to penetration is selected as a preventative measure.This was achieved through a review of worldwide research to identify and document designevents applicable to onshore Australian pipelines, identifying the damage modes and sources ofdamage associated with these design events, identifying methodologies for predicting damageseverity, development of methodologies for design of pipelines against external interference, andfinally identifying areas for further research.

Four design events were identified from literature. These were classified into four arbitrarycategories:

• Category 1 Design Events – caused by machines with backhoe attachments• Category 2 Design Events – caused by machines with drilling attachments• Category 3 Design Events – caused by machines with chain driven digging attachments• Category 4 Design Events – all other events not covered by Categories 1, 2 and 3

Very little information was available on Category 2 and 3 design events, and Category 4 designevents were not within the scope of this report. The bulk of the available literature dealt withCategory 1 design events.

The majority of the research undertaken around the world to date on resistance to externalinterference has been carried out by the European Pipeline Research Group (EPRG), British Gas,Battelle Laboratories, American Gas Association (AGA) and Andrew Palmer and Associates.From this literature, four damage modes were identified for the Category 1 design event:

• Plain Dents• Plain Gouges• Dent and Gouge Combinations• Punctures

Models have been developed by a number of organisations for the prediction of a variety offailure parameters associated with these damage modes. Existing research also indicates thatplain dents and plain gouges are unlikely to cause failure of typical pipelines by themselves – themost severe case of damage, aside from puncture, is a combination of denting and gouging.

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With the exception of the puncture models, there is currently insufficient experimental or actualdata available to apply to any of these models to gain an understanding of the accuracy andreliability in predicting critical failure parameters. Of the puncture models, the Driver 16(1998)equation, based on the Corbin and Vogt17 model for estimating puncture resistance returns theclosest correlation to the available experimental data, and at this point is recommended forpuncture resistance calculations for the Category 1 design event.

A wide variety of data was collected from Category 1 damage source suppliers, resulting in adatabase of approximately 200 machines currently available in Australia. This informationallowed a relationship to be specified between operating weight and digging force, and alsoallowed machines to be grouped into one of four machine classes depending upon their operatingweight. These machine classes allow an easier specification of teeth cutting edge parameters fora machine of a given operating weight. These teeth cutting edge parameters, a required input formost of the predictive damage dent and puncture models, were extracted for a number ofdifferent digging functions such as penetration, abrasion and general purpose applications.

Application of these damage modes and predictive models can be made for Category 1 designevents only at this point in time. Of the four damage modes associated with Category 1 designevents, only the severity of two, denting and puncture, can be directly related back to a particularsize of Category 1 damage source. The predictive models for plain gouging and dent and gougecombinations all return a failure hoop stress that are independent of the damage source, butdependent on defect size. To allow effective use in the risk assessment process, the capability ofdamage sources to produce all four damage modes for this design event need to be quantified,and this forms part of the future research recommendations.

In addition to the Category 1 design event future research mentioned above, other areas forfuture research were identified. Category 2 and 3 design events require significant furtherinvestigation in order to identify and document damage modes and predictive models to enabletheir effective use in the risk assessment process in a similar fashion as the Category 1 designevent.

Applicability of Research to Australian Pipelines and Census of Typical Australian Pipelines

In order to assess the applicability of external interference research undertaken to date, thevarious damage prediction model parameters described within this report were compared totypical Australian pipeline data.

The database consists of 338 pipeline sections based on nominal diameter. Figure 12 depicts thedistribution of the pipeline population with respect to nominal diameter. It is recognised that thisfigure does not depict the true situation of Australian pipelines with respect to populationdistribution, because the total length of pipelines for each diameter is not shown. However, forthe purposes of this report, the diameter is the more crucial parameter when assess theapplicability of the damage modes so far described.

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0

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Nominal Pipeline Diameter

Nu

mb

er o

f P

ipel

ines

Figure 12 - Distribution of Australian Pipelines by Nominal Diameter

These pipeline sections have a range of wall thicknesses, grades and operating pressuresassociated with them. These parameters are shown in Table 1. This table shows that as thenominal diameter increases, the lower end of the material grades used for those diametersgenerally rises, subsequently resulting in larger wall thicknesses. Most of the nominal diametersare subjected to a range of operating pressures, ranging from around about 2.7 MPa to 10.2 MPa.

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Wall Thickness(mm)

Min MaterialGrade/SMYS(MPa)

Max MaterialGrade/SMYS (MPa)

MAOP (MPa)NominalDiameter

Min Max API 5L SMYS API 5L SMYS Min Max

DN50 No information availableDN80 No information availableDN100 4 6.02 B 241 X52 358 2.7 6.9DN150 3.2 7.1 B 241 X65 448 5.1 9.9DN200 3.8 11.9 X42 289 X65 448 2.9 7.4DN250 4.8 6.3 X46 317 X70 482 2.7 7.8DN300 5.2 9.5 N/A N/A N/A N/A 5.0 7.4DN350 5.3 7.6 X52 358 X70 482 6.9 7.4DN400 6.0 9.5 X60 413 X70 482 2.7 10.2DN450 6.7 9.9 X52 358 X70 482 2.7 2.7DN500 8.7 8.7 X65 448 X65 448 6.9 7.1DN550 No information availableDN600 7.9 7.9 N/A N/A N/A N/A 2.7 2.7DN650 8.7 12.7 X65 448 X65 448 8.5 8.5DN700 No information availableDN750 9.5 10.9 X42 289 X60 413 2.7 7.1DN850 8.3 17.5 X65 448 X65 448 6.2 7DN900 No information availableDN950 No information availableDN1000 No information availableDN1050 No information available

Table 1 - Australian Pipeline Physical Properties

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Table 2 details the minimum and maximum parameters ranges for the Category 1 design eventdamage prediction models presented in this report.

Damage Mode Model Diameter Range Wall ThicknessRange

MaterialGrade Range

MAOP Range

Australian Pipeline Values DN50 to DN1050 3.2mm to17.5mm

Gr. B to X70 2.7MPa to10.2MPa

EPRG DN150 to DN900 3.2mm to12.5mm

X42 to X80 Hoop stress upto 72% SMYS

Denting

Spiekhout No parameter information availableDent - Fatigue EPRG DN500 to DN900 7.0mm to

15.9mmX52 to X70 N/A

Keifner No parameter information availableGougingSpiekhout No parameter information availableBG (1982) No parameter information availableBG (1992) No parameter information available

Dent & Gouge

AGA PRC DN400 toDN1000

6.9 mm to 11.6mm

X52 to X65 Not Applicable

Spiekhout(1987)

No parameter information available

Spiekhout(1995)

No parameter information available

Corbin &Vogt

DN200 toDN1200

4.3mm to17.6mm

X46 to X80 Not Applicable

Puncture

Driver DN150 to DN900 4mm to 12.5mm Up to X70 Not Applicable

Table 2 - Damage Prediction Model Parameter Ranges

From the above table, the following may be observed:

• The EPRG denting model is applicable to approximately 90% of Australian pipelines(based on diameter alone), but doesn’t cover diameters less than DN150, or material gradesbelow API 5L X42.

• The EPRG dent fatigue model is only applicable to about 15% of Australian pipelines(based on diameter alone) – those of diameter DN500 and greater. The smallest applicablewall thickness is only 7.0mm.

• The AGA PRC dent and gouge combination model has similar parameter ranges to theEPRG dent model. This model would only be applicable to about 24% of Australianpipelines (based on diameter alone). Note that the wall thickness and material grade rangesare relatively small.

The Corbin & Vogt puncture model is not valid for pipelines of nominal diameter DN150 orsmaller. As a significant number of Australian pipelines are DN150 or smaller, and have wallthickness less than 4.3 mm and grades less than API 5L X46, this model should only be appliedto the larger pipelines. However, this model does return similar results to the Driver model,which is valid for DN150 pipelines, 4 mm wall thickness and all material grades up to API 5LX70.

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It must be noted in the analysis of these damage prediction models, and their respectiveparameter ranges, that these ranges are generally valid for the experimental data used to calibratethese models. These models may well be valid for parameter ranges outside those noted above,but there has usually not been sufficient actual and experimental data available to determine theaccuracy of these models over the full Australian pipeline range of parameters.

Practical Application

At this point in time, the models detailed within this report are only applicable for Category 1design events and will allow the prediction of critical Category 1 design forces and stressesrelated to denting, gouging and puncturing of a pipeline. However, it must be noted that therewas not sufficient data available for the performance of a proper accuracy check of all models atthe time of compiling this report. Therefore, until properly validated and verified, the modelsdetailed in this report should be used at the pipeline engineer’s risk. Generally, these modelstend to have been developed using fairly extensive experimentation and appear to have soundempirical and semi-empirical bases, although it must be noted that all models detailed in thisreport have been developed using typical overseas pipelines and damage sources and not typicalAustralian pipelines and damage sources.

After reviewing the damage prediction models available, it becomes apparent that only theoutput of the denting and the puncture models can be correlated back to a particular machineclass. The gouging and the dent and gouge combination predictive damage models return as aresult the critical failure stress for a defect of given size. These models are completelyindependent of the tool dimensions that created either the gouge or dent and gouge combination,or the force/energy required to create a defect of given dimensions. The implications of this arethat gouging and dent and gouge combinations caused by a Category 1 damage source of aparticular size are not yet able to be predicted. In terms of critical damage modes, dent andgouge combinations are considered severe forms of pipeline damage. Plain gouges are notconsidered as severe damage as dent and gouge combinations, but the ability to predict likelygouge dimensions would be most handy to the pipeline engineer.

CONCLUSIONS

As can be seen from this paper, the Australian pipeline research program is active and has beeninstrumental in ensuring that Australia’s energy pipelines are safe, efficient and cost competitive.It also shows how the industry maintains the Australian Standard for pipelines in step withemerging technology and changes to the operating environment and to ensure that newapproaches to the solution of problems can be incorporated into new and existing pipelines.

The Australian Pipeline Industry Association is pleased to be able to participate in this JointTechnical Meeting and to share in the results of research work on pipelines

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AUTHOR’S BIOGRAPHY

Name: Max J. KimberTitle: Managing DirectorAffiliation: M.J. Kimber Consultants Pty. Ltd., Canberra, ACT, AustraliaQualifications: Bachelor of Engineering with Honours, University of Adelaide,

AustraliaMemberships: Fellow of the Institution of Engineers, Australia (FIEAust)

Fellow of the Australian Institute of Energy (FAIE)Previous Affiliation: General Manager Operations, Pipeline Authority, Canberra (to August

1994)

Mr Kimber has been associated with Australia’s natural gas pipeline industry for 27 years.He is on the Board of the Australian Pipeline Industry Association and represents a cornerstoneinvestor on the Board of a pipeline company. He is Chairman of the pipeline industry’s peakresearch committee and was a member of the PRCI Executive Committee and several PRCISupervisory Committees. He was instrumental in achieving membership of PRCI by Australianpipeline companies in the early 1980s.

He has made significant contributions to new regulatory regimes and technological innovation inthe Australian gas pipeline industry. He provides consulting services to the major corporations,law firms and governments involved in the Australian energy and pipeline industries, includingDuke Energy, Epic Energy (part owned by El Paso), CS Energy, Energex, Governments of NewSouth Wales, Northern Territory, South Australia and Commonwealth.

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REFERENCES 1 Kimber M.J., The changing face of the Australian pipeline industry, Ninth symposium on linepipe research, Pipeline Research Committee, American Gas Association, Houston 30 September- 2 October 1996

2 Henderson I. M., Krishnan K. N., Cantin G.M.D., Investigation of field welding limits for girthwelding thin walled high strength pipes, Final report to the APIA/WTIA Program ManagementCommittee, 22 October 1998

3 Norrish J, Carapic M The feasibility of mechanised girth welding for the installation of landbased transmission pipelines in Australia, Interim report to the APIA/WTIA ProgramManagement Committee, 15 August 1997

4 Norrish, J., Monitoring and Interpretation of Transient Metal Transfer Phenomena in GasMetal Arc Welding, Int. Symposium on Microwave Plasma & Thermo. Process. Of Adv. Matl.,2/97, Osaka, Japan, pp.151-162.

6 Mile Purdevski, Defect Detection of Automated Gas Metal Arc Pipe Welding. Master ofEngineering Thesis, University of Wollongong, Department of Mechanical Engineering, June2000

7 Barbaro, F. J., and Bowie, G. G. Assessment of workmanship defect acceptance levels in highstrength 5mm wall thickness pipeline girth welds, Report to APIA Research ProgramManagement Committee, June 2000

8 Standards Australia, AS2885-1997 Pipelines – Gas & Liquid Petroleum – Part 2 – Welding

9 Hopkins P., Denys R., The background to the proposed European Pipeline Research Group’sgirth weld defect limits for transmission pipelines, Joint EPRG/PRC Conference May 1993

10 Painter, M., In-service welding of gas pipelines, Final report to APIA Research ProgramManagement Committee, June 2000

11 Croker A., Cooper P.,Arfiadi Y., Godbole A., Hadi M., Pipeline hydrostatic testing: pressure/temperature correlation, Final Report to APIA Research Program Management Committee,March 2000

12 Roach I., Pipeline Awareness, Interim Report to APIA Research Program ManagementCommittee, October 2000

13 Standards Australia, AS2885-1997 Pipelines – Gas & Liquid Petroleum – Part 1 – Design

14 Standards Australia, AS2885-1997 Pipelines – Gas & Liquid Petroleum – Part 3 – Operations& Maintenance

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15. Stewart A. J Pipeline Resistance to External Interference Final Report to APIA ResearchProgram Management Committee, January 2001

16 Driver, R., & Zimmerman, T.J.E. (1998)“A Limit States Approach to the Design of Pipelinesfor Mechanical Damage”17th International Conference on Offshore Mechanics and ArcticEngineering American Society of Mechanical Engineers (ASME)

17 Roovers, P., & Steiner, M., & Zarea, M. (n.d) EPRG Recommendations for the Assessment ofthe Tolerance and Resistance of Pipelines to External Damage, European Pipeline ResearchGroup (EPRG) Paper 21