Design, Application and Installation of an X100 Pipeline.pdf

7/25/2019 Design, Application and Installation of an X100 Pipeline.pdf

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1 Copyright 2003 by ASME

Proceedings of OMAE0322

ndInternational Conference on Offshore Mechanics and Arctic Engineering

June 8-13, 2003, Cancun, MEXICO

OMAE2003-37429

DESIGN, APPLICATION AND INSTALLATION OF AN X100 PIPELINE

Alan Glover, Joe Zhou and David HorsleyTransCanada Pipelines Limited., Calgary, Alberta, Canada

Nobuhisa Suzuki, Shigeru Endo and Jun-ichiro TakeharaJFE/NKK Corporation, Tokyo, Japan

ABSTRACTTraditional pipeline technology will be severely

challenged as design-operating pressures continue to rise andgas field developments occur in more remote locationsincluding the arctic. Cost-effective solutions to these issuescan be found through innovative designs using new technology

and its implementation. Some of these designs have consideredthe use of high-pressure natural gas pipelines resulting in thedevelopment of high strength steel. In order to meet theseincreases in pressure TransCanada and JFE/NKK have beenworking extensively on the application of X100 (Grade 690)

linepipe and this has culminated in the construction andinstallation of a X100 project in the fall of 2002. This paperwill discuss the development of the related research projectsthat allowed the successful completion of the field project. The

topics will include the material properties and fracture controlplans for X100. In addition the approach to strain based designfor X100 will include the analysis for both the tensile strainlimits (weld mismatch consideration) and compressive strainlimits (i.e. buckling capacity). The development of the field

welding process will also be covered. The paper will discussthe implications of using X100 from the perspective of thesuccessful field project and the application of a strain-baseddesign.

INTRODUCTIONTraditional pipeline technology will be severely challenged

as design-operating pressures continue to rise and gas field

developments occur in more remote locations including thearctic. Cost-effective solutions to these challenges can befound through innovative designs using new technology and itsimplementation. Some of these designs have considered the

use of increasingly higher natural gas pipelines resulting in thedevelopment as shown in Figure 1. Not only have pressures

changed (and are continuing to increase) but also the regions inwhich gas developments occur are becoming more remote and

in more hostile environments. Discussions on development ogas reserves in the North American arctic have been ongoingsince the 1970s, and many factors have slowed or delayedthose developments. One of the reasons that the pipelines have

not been built is because previous studies have always foundthe cost too high to make the pipeline economically justifiedIn recent years changes in pipeline design and constructiontechnology have the potential for reducing the cost of theseNorthern pipelines substantially. TransCanada PipeLines

(TCPL) and JFE/NKK Corporation have been working onvarious pipeline technologies that will contribute towards thesereductions in costs. Potential arctic designs will also experiencelarge temperature profiles as well as lower gas operating

temperatures and higher secondary loading. In order to provideinnovative solutions to these issues TransCanada has beenutilizing many innovative approaches including the use of highstrength pipeline steels. In order to use these steels manydifferent approaches have had to be developed. The following

material section summarizes the application of Grade 483 andGrade 550 on the TCPL system. In order to accommodatehigher operating pressures, however, higher-grade steels havebeen developed. The application of Grade 690 will be

described on a project that was completed in the fall of 2002These developments will contribute to cost-effective designsand construction for the North.

MATERIALSThe prime impetus for increasing pressure in a gas

pipeline system and related increases in material properties iseconomics. On a large diameter pipeline project in NorthAmerica about 40% of the project cost is related to material, (ina Northern project about 30% of the cost relates to material)

MAT TOC


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and hence reducing material costs has a significant effect onproject costs. A typical relationship is shown in Figure 2,which clearly illustrates the benefit of using higher strengthmaterial and is the driving force for increasing strengths toeven higher values. The figure only illustrates the effect up to

Grade 690 for moderate pressure increases and utilizes Grade

483 as the base analysis. Note that at some of the intermediatepressures that there is no benefit from the increasing strengthlevel. This is because as the pipe material strength increases

this type of relationship has to also take into account D/tpracticalities, fracture control and influence of local bucklingbehaviour (which will be discussed in detail later). Fulladvantage of the higher grades can only really be taking intoaccount once a threshold pressure and wall thickness is

achieved. These factors become particularly important in astrain-based design and applications for the North. This effectis illustrated in Figure 3, which schematically shows that thebenefits of higher strength materials (e.g. Grade 690 or X100)

do not become effective until higher pressures are obtained.

TransCanada introduced high strength steel (grade483, X70) into pipeline applications in the early 1970s. At thesame time higher design factors were implemented i.e. 0.8design factors in Class 1 locations. Since that time over 6300

kms of large diameter Grade 483 pipe has been installed in oursystem resulting in considerable savings for our shippersthrough reduced tonnage. In 1994 and 1995 TransCanadaintroduced the full use of Grade 550 (X80) on a 30 km project

(a small project had been completed in 1991). Since 1995approximately 460 km of Grade 550 has been installed on theTransCanada system. Grade 550 was successfully utilized indiscontinuous permafrost in Northern Alberta. The applicationof Grade 550 on our projects has represented a 12% reduction

in the material costs. Note that for the range of pressures thathave been used, full advantage of the pipe wall reduction canbe achieved.

Grade 550 continues to offer advantages as design

pressures increase but at the high pressures wall thicknessbecomes a limitation and higher strength steels are required.Since 1998 TransCanada and JFE/NKK Corporation have beenworking on the development and application of Grade 690(X100), primarily as a potential application for high-pressure

gas pipelines. These projects have included the understandingof the behaviour of the pipe material, the joining technologyrequired, the application of the material in a strain-based designapproach, fracture behaviour of the material and construction

related issues and have been reported separately in thisconference. As a result of these programs a decision was madein early 2002 to implement Grade 690 on one of the summerconstruction projects. The details of the project are reported ina separate section. The success of this project results from a

technology program that has included:

Pipe Material Properties: All aspects of the materialproperties have been studied as they relate to ordering and

performance. The key issues are around manufacturingprocesses and chemistry, the stress-strain behaviour, yield to

tensile ratios (and how to measure these properties), uniformstrain, hoop and longitudinal properties, long seam weldproperties and toughness requirements. All this work has beencarried out on trial pipes, typically in the NPS 30 and 36 rangeIn addition work is ongoing in terms of the effect of these

parameters on costing trends. The pipe used for the main

project was Grade 690 with a diameter of 1219-mm (48) and awall thickness of 14.3-mm (0.56). Specific details are givenlater.

Joining: The emphasis to date has been on developingmainline mechanized girth welding procedures and manual tie-in procedures. The joining technology has also focussed ondeveloping procedures that would meet our strain-based designfor frost heave and for severe winter service. Procedures have

been developed for mechanized welding using pulsed GMAWusing standard wires and various gas mixtures. A lowhydrogen vertical down manual metal arc procedure or avertical up flux cored procedure is available for tie-in weldsConsiderable work is still underway, and this relates primarily

to higher productivity process/procedure and tie-in proceduresRecent developments include twin wire, twin torchapplications.

Inspection: Standard inspection procedures can be used onGrade 690 production welds, primarily using mechanized

ultrasonic inspection. Work was performed on defecdetection, flaw acceptance and velocity calibrations.

Bending: Collaborative work showed that no issues would beexpected on bending of Grade 690. This work extended theanalysis performed on Grade 550, and the effect of springback

In addition analyses were performed by CRC Evans to showthat the existing 48-inch bending machines would be capable ofbending pipe up to at least 16-mm wall. The results show thathe bends would require additional pulls to obtain the same

bend as compared to Grade 550. Collaborative work with BPon a limited bending trial on NPS 36 Grade 690, alsoconfirmed the additional pulls.

Fracture Behaviour: Two full-scale fracture tests have beencompleted on Grade 690 material as part of a Group Sponsored

project funded by TransCanada, BP, Alliance and BGInternational and led by Advantica Technologies with supporfrom the Japanese steel and pipe makers. The two tests wereperformed on NPS 36 material with wall thickness onominally 13.2 mm and 14.8 mm, at test pressures of 13,600

kPa (1972 psi) and 18,000 kPa (2610 psi). Both tests weresuccessful and fracture arrest was as predicted. The predictionof fracture arrest was based on a correlation with Charpytoughness and a correction factor. TransCanada is currently

working on an improved way of predicting the toughnessrequired for arrest that will eliminate the need for arbitrarycorrection factors for both Grade 550 and 690. Nonetheless thepresent full-scale results were used to develop the requirementsfor material specifications for the prevention of fracture

propagation. Additional work is also being carried out on thegas decompression characteristics of high-pressure gases andthis will become an important issue for those designs. Work


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also continues on a collaborative program with the Europeansthat will further extend the database on full scale fracture testsfor Grade 690.

Strain-Based Design: Extensive work is being performedon developing the tensile and compressive strain limits

applicable to a high pressure design using high strength steel.

While these will not be required for this initial Grade 690project (it will be a stress-based design), elements of it will beincorporated into the approach including the defect toleranceapproach. This work has concentrated on the specification of

weld/pipe properties to achieve satisfactory tensile strain limits,and on the numerical analysis of the approach. The localbuckling/post-buckling program continues to define thecompressive strain limit, however emphasis is on the material

behaviour in the post-buckling mode. This particular aspect isreported separately in this conference.

Canadian CSA Code Implementation: While all of theresearch work was being performed TransCanada was active indeveloping acceptance of Grade 690 into the relevant CSA

codes. This resulted in incorporation of Grade 690 into thenew edition of CSA Z245.1-2002, which was ultimatelypublished in the fall of 2002. TransCanada utilized this in itsapplication to the Alberta Energy Utilities Board for approvalto utilize Grade 690. Close cooperation with the regulatory and

Code bodies was an important step in the rapid implementationof this technology.

Applicability of Grade 690: In designing the application ofhigh strength steels (particularly for the North) and wherebenefits can be achieved it is necessary to balance the

requirements of wall thickness requirements for pressure,fracture control and buckling resistance (frost heave and thawsettlement). While the pressure is a simple relationship, thefracture and buckling capacity are a complex series of

interrelationships. In some cases increased wall thickness maybe required to provide fracture arrest, however as the pressureincreases for high-pressure designs the driving force reducesand the relationship changes. Buckling capacity is a complexrelationship between strength (and stress-strain behaviour),

moment capacity and D/t ratios. This becomes apparent at thelower pressures where Grade 690 offers no advantage over theconventional Grade 550, however at high-pressures the reverseis true.

WESTPATH PROJECT AND INSTALLATION OFGRADE 690

Early in February 2002 an internal decision was made to

implement Grade 690 on one of the summer expansionprojects. This was followed up by a presentation to theOperations Committee with a recommendation to proceed withthe installation of 1 km of NPS 48 on the Westpath project.

The Westpath project (Figure 4) involves building new

segments of the TransCanada pipeline system in Alberta andBritish Columbia to help meet long-term growth gas demand inthe western United States and California markets. The 2002

$115 million project entailed building more than 86 kilometersof pipeline loop along our existing system. The pipelineproject consists of 64 kms of Grade 550 NPS 48 and 22 kms ofNPS 20. The project also involves the addition of onecompressor station in Alberta, and modifications to the Elko

and Moyie compressor stations in BC. Adding to the

complexity is the fact that the Alberta System is regulatedunder the Alberta Energy and Utilities Board, whereas the BCSystem fall under National Energy Board jurisdiction. As a

result, the approvals for Westpath involved both the AEUB andthe NEB.

The specific installation of Grade 690 took place on theAlberta Mainline Loop # 2 (Saratoga Section) in Alberta whichconsisted 20.9 kilometers (13.6 miles) of 1219-millimetre (48-

inch) pipeline Grade 550 and 1.0 kilometers of 1219 mm (48inch) Grade 690. The schematic for the Saratoga loop is shownin Figure 5.

The pipe material was supplied by JFE/NKK and ordered

to the CSA Z245-02 requirements plus TransCanadas

additional internal specification. The internal specificationplaces a much tighter tolerance on the pipe requirements thanthe CSA code. One of the prime objectives of the project wato gain experience in the manufacturing and construction of

Grade 690 so that it could be applied to future high-pressureprojects. The specific Saratoga project only required a designof NPS 48 Grade 550 with a wall thickness of 12-mm. In ordeto meet the objectives of the project and to develop longer-term

requirements for high-pressure designs it was decided to utilizeNPS 48 Grade 690 with a wall thickness of 14.3-mm for the 1km section of Saratoga. The design requirements for the pipewere therefore based on that premise. This requirement meanthat some rapid development was required at JFE/NKK

resulting in some slight modifications to the U and O procedureand to some of the welding requirements. Nonetheless all othe technical and delivery requirements were met.

One key aspect of the specification of the material was

agreement on the type of testing to be performed to verify thematerial minimum specified yield strength in the hoopdirection. Traditionally pipe material has been qualified usingthe flattened strap specimen. TransCanada, along with otherhas been evaluating the behaviour of high strength materials

using the flattened strap, round bar and ring expansion testsThe results of these tests have shown that the flattened strappresents a misleading approach to pipeline design because othe Bauschinger effect and that the round bar test is an effective

method to qualify the material. This effect is particularlypronounced for steels with strength levels greater than Grade550 (Figure 6). The challenge is that if using a flattened strapto qualify then the actual material yield strength is much higherand the Y/T ratio becomes very high and often will exceed

0.96. Based on these analyses it was agreed that the Grade 690pipe material would be qualified on the round bar procedureThe flattened strap results were, however, collected to add tothe database and part of the continuing effort to have code

acceptance of the approach. Additional tests were also


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specified for the longitudinal stress-strain behaviour. Theseresults were for information purposes only but form part of thestrain-based design for the tensile strain criteria (namelyovermatching of the weld yield to pipe yield). All of the resultsand comparison with the specification are given in Tables 1,2

and 3.

The results of the chemical analyses show that the pipemet the additional requirements of TCPL P-04, with a productCE of 0.26, typical of the prior trials. The results of the tensile

properties (Table 2) show that the pipes met the Grade 690requirements of both CSA and P-04 when qualified with theround bar specimen and as required. The average yield andultimate were 763 MPa and 838 MPa respectively, with a Y/Tof 0.91 (note that the maximum Y/T was 0.95). As expected

the flattened strap results did not meet the requirements interms of yield of the CSA code, note as well that the Y/T ofthese specimens is much lower, again as expected. Our resultsare also in agreement with the results published in Figure 6.

The longitudinal properties of the pipe gave slightly lower

yield and ultimate, and this was a deliberate action to enable amore efficient strain based design for the tensile strain limits(see later section). The flattened strap transverse weld samplesall met the CSA and P-04 requirements.

The fracture toughness property requirements of the pipeand weld were determined based on a fracture initiation andpropagation control plan. The fracture arrest properties werebased on correlations from the full-scale fracture tests and from

conventional models with a correction factor. All of thefracture toughness properties (Table 3) met those requirements.Note CSA Z245.1 only addresses nominal pipe bodytoughness. CSA Z662 (design requirements), addresses therequirements for fracture initiation and arrest design, and for

higher pressures and stresses requires a full engineeringanalysis.

A key requirement for the construction and installation ofGrade 690 was the qualification of the various welding

procedures. For the mainline this consisted of mechanized gasmetal arc procedures and for the tie-ins manual metal arcprocedures. The summary of the procedures is as follows:1) Mechanized Gas Metal Arc Welding (GMAW) with a

vertical down welding progression were used for all mainline

welds as follows

Internal root beads shall be completed using short circuitmetal transfer with 75% Ar - 25% CO2 shielding gasmixture and 0.9 mm Thyssen K-Nova wire

External weld passes shall be completed using pulsed gasmetal arc welding with a 85 %Ar - 15%CO2 shielding gas

mixture and 1.0 mm Oerlikon Carbofil NiMo-1 wire.

External cap pass shall be completed using short circuitmetal arc welding with a 85 %Ar - 15%CO2 shielding gasmixture and 1.0 mm Oerlikon Carbofil NiMo-1 wire

100C minimum preheat shall be maintained throughout.2) Tie-in welds were completed using the shielded metal arc

welding (SMAW) process with a vertical down weldingprogression as follows:

Root beads shall be completed with E5510-G (E8010-G)

minimum preheat 100C maintained throughout

Hot, fill and cap passes shall be completed with 4.0 mmBohler BVD 110 (E11018-G)

Contractor shall ensure that there is no pipe movement untiafter completion of the hot pass and there shall be a 24 hour

delay prior to inspection for all shielded metal arc welds

All of the welding procedures were qualified by both thecontractor and by TransCanada to meet the relevant CSA codesand to be used for both workmanship and alternative

acceptance criteria according to Appendix K of CSA Z662-99Typical results from the procedure qualifications gave themechanized girth weld with average yield strengths of 698MPa and ultimate strength of 815 MPa. The respective cros

weld tensile tests results all failed in the pipe material and gavecorresponding pipe longitudinal properties of yield strength675 MPa and ultimate strength 811 MPa. Note theselongitudinal properties are slightly higher than those reported

for the pipe qualification in Table 2 (623 MPa yield and 801MPa ultimate), however that is not unusual when performingcross weld tests. In either case however the girth weldproperties overmatched those of the pipe longitudinaproperties and that was one of the main criteria. Additionally

prior to the commencement of the project detailed workingsessions were held with the contractor and for the welders thewelding procedures. This required that an extra welder trainingschool was set up immediately prior to kick off to re-train thewelders to utilize the pulsed gas metal arc procedures. This

was necessary in this particular case because the welders hadbeen on the overall Westpath project all summer constructingthe Grade 550 using mechanized short circuit gas metal arc

procedures. The change over to the pulsed procedures requiredsome additional training and also requalification. Views of theinternal and external welding are given in Figures 7 and 8.

Another potential issue with Grade 690 could have beenthe field bending. As described earlier some preliminary trial

had been performed on NPS 36 and also calculations to showthat the bending could be performed using a standard CRCbending machine with an internal mandrel. Nonethelessbecause of the timing of the project and the delivery of thepipe, it was not possible to do any pre-bending trials on the

NPS 48 Grade 690 material. Even so the field bending wenextremely well. No problems were experienced with thebending, no coating issues arose, the pull times were similar to

the Grade 550 project, and slightly shorter pulls were used tocompensate for the additional springback. Overall bends of 1degree per pipe diameter were easily achieved. The layout othe pipe for the field project is shown in Figure 9.

Final field installation of Grade 690 took place in lateSeptember 2002. After successfully training of the welders al

of the welding was completed over a 2-day period. The pipesused for the project were all approximately 12 m in length andno double jointing was performed. The pipes were left as


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single joints to permit the maximum number of welds to becompleted for the relatively short project. All of the pipes werecoated using standard fusion bond epoxy coating, with thenormal cut back to allow full ultrasonic inspection (Figure 10).All of the field welding and inspection proceeded as planned.

Some lack of fusion defects were experienced, however, these

were all related to ongoing welder training as opposed towelding process. Weld repair rates were similar to our otherstart up mainline projects. Work is continuing to increase field

welding productivity using automated processes and these willbe introduced in the summer of 2003.

Complete hydrostatic testing of the line was performed inearly October and the line was placed in service November 1st2002. Final meetings have been held with the regulatory

bodies to complete the information feedback loop in terms ofperformance of the Grade 690 material. The pipe material isnow considered as acceptable for use in high pressure andstrain based designs. The following section describes theapproach that will be utilized on our strain-based design.

APPLICATION OF GRADE 690 IN A STRAIN BASEDDESIGN

Strain-Based DesignStrain based design applies to a subset of the limit states

where displacement-controlled loads dominate the pipelineresponse. This would be typical for a pipeline design in the

arctic where secondary loads from ground movement woulddominate. In its application a procedure is also developed toestablish safety factors. Note limit states are typicallyclassified into one of several broad categories, such as safety,

operability, and serviceability. Design criteria can then beapplied for example in terms of the external loading ordisplacement conditions giving rise to the occurrence of eachlimit state.

Load EventsThe normal operating loads are determined from the

project Maximum Allowable Pressure and include any

contribution from the temperature differential between theoperating and installation conditions. During installation, thepipeline is subjected to temporary installation loads such asbending during laying and lowering. During operation anddependent on the surrounding conditions, the pipeline may be

subjected to various external loads such as fault displacement,ground movement, frost heave, thaw settlement and others. Allthese loads and the design checks for them need to be described.Dependent on the nature of a load event, it can be classified as

a load-controlled event or a displacement-controlled event. Ina load-controlled event, the magnitude of the load isindependent from the displacement and deformation of thestructure that the load applies to. Typical examples of load-controlled loads include self-weight, internal pressure, and the

constant external loads (forces) applied to the structure. A

load-controlled load is often described in terms of the directionand magnitude of the applied force. In a displacementcontrolled event, the magnitude of the load applied to thestructure is dependent on the displacement and deformation ofthe structure. Typical examples of displacement-controlled load

events are thermal expansion, frost heave, and imposed

displacements.The significant difference between the load-controlled anddisplacement-controlled events is that the structural responses

are fundamentally different beyond the peak load, asconceptually shown in Figure 11. In the figure a steel baloaded with a pulling force P is shown in (a) as an example of asystem with a load-controlled load. Similarly, the same steebar is loaded with tensile displacement in (b) as an example

of a system with a displacement-controlled load. If the appliedload P and the imposed displacement increase consistentlythe structural responses of the load-controlled system (a) andthe displacement-controlled system (b) are identical as shown

in (c) until the ultimate stress is reached. At the ultimate stres

then a steel bar subjected to a load-controlled load fails in theform of rupture. Whereas a steel bar subjected to adisplacement-controlled load maintains its integrity and the

deformation process afterward remains stable and controlleduntil the failure strain is reached.

For a structure with more complicated failure mechanismssuch as local buckling, the fundamental difference of thestructural responses to a load-controlled event and a

displacement-controlled event remains the same while the peakload (ultimate stress in above example) may be establisheddifferently according to their specific failure mechanismsSimilarly, the strength and deformation capacity governs the

resistances of a structure to load-and displacement-controlledloads, respectively. Consequently, design criteria are eitherstrength-based or strain-based for load- or displacement-controlled systems, respectively.

The applicable limit states for a particular pipeline are

determined based on potential and practical failure modesrelevant to the structure under the specific condition. Two keylimit states are determined to be failure of the weldments(tensile limit) and piping local buckling (compressive limit).

Tensile Limit State ApproachTraditionally weld metal defects in pipeline girth welds

were accepted using workmanship based acceptance criteria

These criteria have varied from country to country, howeverthey have all been shown to be safe and conservative. This isbecause the criteria were originally based on what wasconsidered to be a good level of welding workmanship and

have evolved over many years. While these criteria have beenshown to be safe, they do not have any basis in terms of designof the pipeline, the loading on the pipeline, nor the materialsutilized in the construction of the pipeline.

In order to take advantage of changing welding

technology and cost-effective design solutions, many countrieshave developed alternative methods for defect acceptance


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standards [CSA 1999 App K, AS-2885 1995, and API 1104App A]. These alternative methods are all based on a fracturemechanics approach and the acceptance criteria were developedusing relationships between defect size, material toughness andstress conditions. Many of the standards have utilized

primarily a fracture and plastic collapse analysis, either

separately or combined within a failure assessment diagram.These approaches have been applied for many years withinCanada [Glover 1981 and 1986], and recently within the

United States [Oil and Gas 1999]; all of these approaches,however, were stress-based. The choice of a stress-basedassessment technique is most appropriate under loadcontrolled situations where the applied stress is low enoughthat both the weld metal and pipe remain within their elastic

stress-strain response limits. When a pipeline is subjected todisplacement controlled loading, the applied strain mayexceed yield strain. For non-elastic longitudinal deformations,the traditional stress based design criteria are inappropriate to

establish the relationship between defect tolerance and global

(pipe and girth weld) plastic straining capacity.A typical strain-based design includes setting limits onoverall strain. The approach requires the understanding of thecollapse approach, and understanding the relationship between

the pipe and the weld properties, as well as defining a failurecriterion. This approach can be utilized when sufficientinformation is known about the basic pipe and weld propertiesand the original acceptance criteria utilized. TransCanada

Pipelines has been utilizing a strain-based approach for designfor several years and it is based on defining the tensile andcompressive strain limits. Generally speaking it has beenshown that the tensile strain limit can be increased if the weldmetal yield strength overmatches the pipe yield strength and

adequate toughness is achieved in the weld. In overmatchingwelds the strain preferentially develops in the pipe material,thereby shielding the weld from large plastic strains. If theweld metal yield strength undermatches the pipe then increased

toughness in the weld is required to provide increasedresistance to the high strains that will develop in the weld.Nonetheless, in undermatching circumstances, the limit ontensile strain is reduced. If the weld undermatches by too much,net section yielding will always control failure and the

allowable strain limit will be severely restricted. This approachhas been validated through a series of wide plate tests and finiteelement modelling [Denys and Glover, 1994, Minami et al,1995]

The results from the FEA and wide plate tests demonstrate that:

An acceptance criteria (allowable strain for a given defectsize) can be developed based on measured strain andvalidated through full-scale tests.

Observation of many test results shows :

1. Failure strain> 0.5% results in Gross Section Yielding2. Failure strain< 0.5% results in Net Section Yielding orFracture3. Failure strain is reduced at high pipe Yield/Tensile ratios

4. Failure strain is reduced as the undermatching level ofthe weld to pipe yield strength increases.

Hence by determining the distribution of properties withinthe pipe and weld one is able to develop an approach for the

acceptable strain limit. This overall approach includes

consideration of mismatch and Y/T effects on the tensile strainlimits. Previous work [Horsley et al 1997] has shown that weldmetal failure is expected to be controlled by gross section

yielding provided that the weld metal matches or overmatchesthe pipe properties, and adequate toughness is achieved. Inaddition if the weld undermatches the pipe slightly, then grosssection yielding can be obtained if the weld has reasonabletoughness, the defect size is not too large, and some

reinforcement is present.This overall approach has been validated using a series of

wide plate tests and incorporated into some standardizedapproaches (e.g. EPRG guidelines for defect acceptance

Hopkins and Denys 1993). In addition FEA modelling

performed also showed that higher strains could be anticipatedfor shorter defects. The limitation with the modelling approachwas that a failure criteria needs to be defined, which iscurrently based on flow stress and this tends to underpredict the

behaviour for overmatched welds. The wide plate databasealso showed the influence of the undermatching andovermatching on the failure strains, as well as the effect ofyield to tensile ratio and the influence of defect size. This

overall approach has been confirmed using a series of projectspecific wide plate tests. The results clearly showed that highestrains to failure are obtained for small defects for theovermatched welds compared to the equivalent undermatchedwelds. The results also confirm that the premise of using an

overmatched weld with small defects allows higher strains tofailure to be achieved. Using this approach, criteria can beestablished that will relate the failure strain to the tolerabledefect size. These criteria will be linked to the pipe and weld

properties and the inspection requirement for the weld. Abalance will then be achieved between the tensile strain limiand the compressive strain limit for the specific loadingscenario. This approach has several implicit safety factorsalready included in the analysis. Although these implicit safety

factors are important it is also recommended that a safety factorbe defined. To date the approach outlined in the BS 8010: Par3: 1993, Code of Practice for Pipelines subsea: designconstruction and installation has been used. In this approach

the standard states that for situations where the displacementsof the pipe are bounded then the maximum allowable strainshould include a safety factor of 1.5.

Compressive Strain LimitLocal buckl ing of Pipe Section

When the pipeline is subjected to compressive loadsand/or bending moments, all or a portion of the pipe cross-section is experiencing compressive stresses and strains. Whenthe maximum compressive strain reaches a critical level, loca


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buckling/wrinkling initiates in the pipe wall. As thecompressive strains increase, the wrinkle continues to developwhich induces significant local deformation and as a result thecapacity to carry compressive loads is greatly reduced in thebuckled areas. If the primary load is load-controlled, local

buckling may immediately lead to significant cross-sectional

deformation and/or material failure (loss of pressurecontainment). In the case of displacement-controlled loads, thedevelopment of local buckling increases the localization of the

deformation at the wrinkle and accelerates the accumulation ofthe strains. However, the pipe typically has significantremaining deformation capacity beyond the onset(initialization) of the local buckling before a true failurecondition occurs.

Extensive research has been conducted on the subject oflocal buckling, wrinkling and post-buckling behaviour of pipein the last three decades [Bouwkamp and Stephen, 1973;Gellin, 1980; Gresnigt, 1986; Lara, 1987; Mohareb, et. al.,

1993; Zimmerman, et. al., 1994; Zhou and Murray, 1995;

Yoosef-Ghodsi, et. al., 1995; Dorey, et. al., 1999; Das, et. al.,2000]. The experimental and analytical studies have led to in-depth understanding on the initiation and development of localbuckling and wrinkling. In general for common modern steel

pipes, the initiation of local buckling was found to be primarilydependent on the D/t (pipe diameter to thickness) ratio and theinternal pressure, and to a lesser degree on factors includingpipe material properties, applied load combination, soil

restraints, initial geometric imperfection, and residual stress.The initiation of local buckling is commonly represented

by the local buckling strain which is often defined as the totalcompressive strain corresponding to the peak load in a load-displacement (e.g. moment-curvature) curve. The D/t ratio has

significant influence on the magnitude of the local bucklingstrain. Increase in D/t ratio tends to reduce the local buckling.The internal pressure dictates the local buckling modes. Atzero or a very low level of internal pressure, a typical local

buckling mode is shown in Figure 12a which is often referredto as the diamond mode. At an intermediate to high level ofinternal pressure, a typical local buckling mode is shown inFigure 12b which is often referred to as the bulging mode.Because of the different modes, the level of internal pressure

substantially influences the magnitude of the local bucklingstrain. The local buckling strain increases as the internalpressure level increases.

Based on numerous test data, a number of predictive

empirical equations have been developed to predict the localbuckling strain [Gellin, 1980; Gresnigt, 1986; BS8010, 1993;Zimmerman, et. al., 1994; CSA, 1999]. Among all theequations, the majority of them are intended for pipe underpure bending, in other words, the effect of internal pressure is

not included. Overall equations developed by Gresnigt (1986),Zimmerman et. al. (1994) and Dorey et. al. (2001) are moreappropriate for large size pipes subject to complex loadingconditions.

Post-Buckling of Pipe Section

For a pipeline subjected to load-controlled loads, the

initiation of local buckling (or the peak load) is considered tobe representative of the ultimate failure condition that isdefined as loss of containment or collapse of pipe cross sectionThis is because the structural response in the post-buckling

regime is unstable and uncontrolled and the unstable processeventually leads to failure. For a pipeline subjected todisplacement-controlled loads, the initiation of local buckling isno longer a failure condition because of the inherent stability inthe displacement-controlled loading process in the post

buckling regime. It has been repeatedly demonstrated by fullscale experiments [Gresnigt, 1986; Zimmerman, et. al. 1994Dorey, et. al., 1999; Das, et. al., 2000] that pipes havetremendous deformation capacity beyond the initiation of loca

buckling. A recent test program, has studied various loadcombinations (internal pressure, axial load/displacementbending deformation), and pipe specifications. It is concludedfrom the test program that the pipe materials are highly ductile

and do not fail (loss of containment) when they are subjected tomonotonically increasing compressive strain and before thewrinkle is fully developed and the faces are in contact.

Compressive Strain L imi ts and Safety Factors

For pipelines in permafrost areas, the loads that couldpotentially induce excessive stresses and strains include frosheave, thaw settlement, slope movement and temperature

differential. It is apparent, based on the mechanism for theseload events, that these loads are displacement-controlled loadsFor displacement controlled loads, the initiation of locabuckling is not a failure condition for a pipeline. It is, howeverrecommended that compressive strain limits be established

based on the local buckling strain with a safety factor of 1.0Note this represents the initiation of local buckling and isdefined at the peak load point on a load-displacement curve, forthe following reasons. First of all, once a wrinkle initiates, i

develops relatively quickly because of the reduced loadcarrying capacity in the wrinkled section. A developed wrinklehas significant local deformation of the pipe wall and pipecross-section that may affect the functionality of the pipelineIn addition, the current industrial practices of pipe-soi

interaction analysis are based on models where pipe issimulated by a series of beam elements. The beam elements arenot able to properly simulate the local pipe wall and crosssectional deformations, and consequently, a compressive strain

limit beyond the local buckling strain would be difficult toimplement in the design process.

For any given pipeline with defined pipe specificationsmaterial properties, manufacturing process and associatedoperating conditions, then the compressive strain limit can be

established by utilizing an empirical equation. Supplementavalidation of the predicted compressive strain limit can beprovided by full scale local buckling tests when project specificpipes are available. Since the compressive strain limit is

established based on maintaining the pipeline functionality andany limitation on the current practice in pipe-soil interaction


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analyses, rather than the pipeline failure condition, hence theremaining safety margin associated with this limit issignificantly larger than what would normally be required.

FROST HEAVE AND THAW SETTLEMENT

Permafrost presents a unique challenge to the design andconstruction of a northern pipeline. Design for frost heave andthaw settlement in permafrost can be one of the most

challenging aspects of a northern pipeline. To adequatelydesign for permafrost, balanced efforts on various aspects inthe following are required to achieve optimum overallperformance and effectiveness:

Establish appropriate pipeline operating strategies andconditions, especially the temperature profile along the

ROW and the temperature cycle over time. This task iscommonly accomplished through a series of hydraulicsimulations of the pipeline system, including configurationof surface facilities such as compressors and chillers.

Predict frost heave and thaw settlement over the entiredesign life of the pipeline based on a thoroughunderstanding of soil, climate, and pipeline operatingconditions. This task is often accomplished through aseries of geothermal analysis for representative sections

and unique sections of the ROW.

Predict pipeline response resulting from the predicted frostheave and thaw settlement, and comparing the predictedmaximum strains to the strain-based design criteriadiscussed in the previous sections. This task is normally

accomplished through a series of pipeline structuralanalyses, which include two main components: a definitionof the characteristics of soil springs that represents the soil-

to-pipe load transfer mechanism, and a pipe-soilinteraction analysis to determine the pipeline response to

the imposed frost heave and thaw settlement.

While the design process is divided into three aspects, it isimportant to recognize the linkages and coupling effects among

them. It is obvious that operating conditions have a direct andsignificant effect on the ground thermal state. The groundthermal state also has an effect on the pipeline temperatureprofile with varying degrees of sensitivity. Similarly, themagnitude and rate of frost heave and thaw settlement are

dependent on not only the ground thermal state but also thepipeline response resulting from the imposed frost heave and

thaw settlement. The interactive nature of the design processfor frost heave and thaw settlement requires integrated design

tools and process that are able to:

Capture the coupling effect and determine reliably andaccurately the frost heave, thaw settlement and pipelineresponse;

Optimize the pipeline design, facility configuration andoperating strategies based on the overall system

performance and cost effectiveness;

Optimize the life cycle cost by balancing initial capital cost

and the ongoing operating and maintenance cost.The overall design process and frost heave and thaw settlementthat TransCanada has been developing is conceptuallyillustrated in Figure 13.

SUMMARYChallenges in pipeline applications will continue to be me

though the application of innovative technologies and the use

of high strength pipeline steels. It has been shown that thesetechnologies can provide safe and reliable systems whilst at thesame time enabling cost-effective solutions. TransCanadaPipeLines has been at the forefront of some of these changesand continues to seek alternative solutions that will drive down

the cost of major projects. The use of higher strength pipelinematerials, alternative pipeline materials, innovative designsincluding strain and reliability-based approaches, structuraintegrity solutions and alternative construction technologies are

all contributing to the ability to meet these challenges. Some othese challenges can be met through the use of high strengthpipeline technology. TransCanada together with JFE/NKKhave successfully developed and installed Grade 690 (X100) aspart of the Westpath project in the fall of 2002. The use o

Grade 690 for these challenging environments has now beensuccessfully demonstrated and will now be part of costeffective solutions for high-pressure pipeline systems.

REFERENCESAmerican Petroleum Institute, (1994), API Standard 1104-18th

Edition, App A, May.

Australian Standard, (1995), AS-2885.2: 1995, Part 2Welding

Bouwkamp, J.G. and Stephen, R.M., (1973), Large DiameterPipe Under Combined Loading, ASCE, TransportationEngineering Journal, Vol. 99, No. TE3, pp. 521-536.

BS8010, (1993), Code of Practice for Pipelines, Part 3Pipelines Subsea: Design, Construction andInstallation, British Standard Institute.

CSA (1999), CSA Z-662-99, Oil and Gas Pipeline Systems

Appendix KDas, S., Cheng, J.J.R., Murray, D.W., Wilkie, S.A., and Zhou

Z.J., (2000), Laboratory Study of Local BucklingWrinkling Development, and Strain for NPS12 Line

Pipe, Proceeding of International Pipeline ConferenceOctober.

Denys R and Glover A.G., (1994), Conf. Mismatching ofwelds, ESIS 17, London

Dorey, A.B., Murray, D.W., Cheng, J.J.R., Grondin, G.Y. and

Zhou, Z.J., (1999), Testing and Experimental Resultsfor NPS 30 Line Pipe Under Combined LoadsProceeding of the 18th OMAE Conference, Paper NoOMAE99/PIPE-5022.


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Dorey, A.B., Cheng, J.J.R., and Murray, D.W., (2001), CriticalBuckling Strains for Energy Pipelines, StructuralEngineering Report No. 237, Dept. of Civil andEnvironmental Engineering, University of Alberta,Edmonton, Alberta, Canada.

Gellin, S., (1980), The Plastic Buckling of Long Cylindrical

Shells Under Pure Bending, Int. Journal of Solids andStructures, Vol. 16.Glover, A.G., Coote, R.I., and Pick, R.J., (1981), "ECA of

pipeline girth welds," Int. Conf. on Fitness for PurposeValidation of Welded Constructions, London,November

Glover, A.G., Coote, R.I., and Pick, R.J., (1986), "Alternativegirth weld acceptance in the Canadian gas pipeline

code," 3rd Int. Conf. on Welding and Performance ofPipelines, London, November

Gresnigt, A.M., (1986), Plastic Design of Buried SteelPipelines in Settlement Areas, Heron, Volume 31, No.

4.

Horsley D.J, Glover A.G. and Denys R. (1997), An assessmenttechnique for defects in under and overmatched pipelinegirth welds PRCi/EPRG, 11thBiennial Joint TechnicalMeeting on Line Pipe Research, Arlington, Virginia.

Hopkins, P and Denys R., (1993), Background to the EPRGsGirth Weld Limits for Transmission Pipelines,EPRG/PRCi, 9th Biennial Meeting on Line PipeResearch,

Knauf G. and Spiekout J. (2002), 3R International Special

Edition 13/2002Lara, P.F., (1987), Revisiting the Failure Criteria of Buried

Pipelines, ASME, Petroleum Division (Publication),PD. Vol. 6, pp. 143-154.

Minami F et al, (1995), Pipeline Technology Conference,Ostend, Belgium,

Mohareb, M., Alexander, S.D.B., Kulak, G.L., and Murray,D.W., (1993), Lab Testing of Line Pipe to DetermineDeformational Behaviour, Proc. 12th OMAE Conf,

Vol. V,Oil and Gas Journal (1999), Article on the Alliance PipelineYoosef-Ghodsi, N., Kulak, G.L., and Murray, D.W., (1995),

Some Test Results for Wrinkling of Girth-Welded Line

Pipe, Proceeding of 14thOMAE Conference, Vol. V,Zhou, Z.J. and Murray, D.W., (1995), Analysis of Post-

Buckling Behaviour of Line Pipe Subjected toCombined Loads, Int. Journal of Solids and Structures,Vol. 32, No. 20.

Zimmerman, T.J.E., Stephens, M.J., DeGeer, D.D., and Chen,

Q., (1994), Compressive Strain Limits for Buried

Pipelines, Centre for Engineering Research (C-FER),

200 Karl Clark Road, Edmonton, Alberta, Canada.

0

5000

10000

15000

20000

25000

1900 1920 1940 1960 1980 2000 2020

Year

Pressure

kPa

Figure 1 Pipeline system operating pressures by year

85

90

95

100

105

110

448 483 550 690

SMYS

% Cost

7000 kPa

8000 kPa

9000 kPa

10000 kPa

12000 kPa

15000

Figure 2 Effect of Pipe grade on overall project costs as a

function of pressure design using Grade 483 as a base

Wall thickness and pressure as a

function of D/t limitation

0

20

40

60

80

100

120

1260 1440 1760

Pressure psi

Wallthickness

factor X80

X100

Figure 3 Beneficial effect of increasing pipe grade as a

function of pressure but factoring in D/t limitations


10/12


Table 1 Chemical analysis

Heat and Product Analysis (weight %)Type ofAnalysis C Si Mn P S Cu Ni Cr Mo Nb V

V +

NbTi N CE

Max. Max. Max. Max. Max. NS NS NS NS Max. Max. NS Max. NS Max.CSA Z245.1-02

(Heat & product) 0.26 0.50 2.00 0.030 0.035 0.11 0.11 0.11 0.40

Max. Max. Max. Max. Max. Max. Max. Max. Max. Max. Max. Max. 0.004 Max. Max.TCPL P-04 & TA #2, Rev. 0

(Heat & product) 0.07 0.35 1.95 0.020 0.001 0.30 0.30 0.10 0.30 0.06 0.02 0.08 0.020 0.009 0.320

Actual (Average) L adle 0.06 0.10 1.87 0.009 0.001 0.27 0.14 0.03 0.22 0.05 0.00 0.05 0.009 0.005 0.28

Actual (Average Product 0.05 0.09 1.87 0.009 0.001 0.28 0.13 0.03 0.21 0.05 0.00 0.04 0.008 0.005 0.26

Table 2 Tensile properties

Pipe Body - Transverse Pipe body - Longitudinal Weld -Transverse

Flattened Strap Specimens Round Bar Specimens Round Bar SpecimensFlattened Strap

Specimens

YS TS EL Y/T YS TS EL Y/T YS TS EL Y/T TS EL

Spec &

Heat

No. For

Grade 690

Production

MPa MPa % Ratio MPa MPa % Ratio MPa MPa % Ratio MPa %

690 760 Min Max. 690 760 Min Max. NS NS NS NS 760 MinCSAZ245.1-02 825 970 17 0.93 825 970 11 0.93 970 10

NS NS NS NS 690 760 Min NS NS NS NS NS Min MinTCPL P-04 and

TA #2, Rev. 0 825 970 11 760 10

Actual Average 684 846 27 0.81 763 838 21 0.91 623 801 22.3 0.78 811 12.4

Table 3 Fracture toughness properties

Pipe Body, Weld, and Heat Affected Zone Toughness Transverse Specimens

Charpy Impact Tests @ -5C Drop Weight Tear Tests @ -5C

Body

(any heat)

Body

(AHA)Weld H.A.Z. Energy

Shear

(any heat)

Shear

(AHA)

Spec &

Heat

No. For

Grade 690

Production

Value (J) (J) (J) (J) (J) (%) (%)

CSA

Z245.1-0240 NS NS NS 50 85

TCPL P-04 &

TA #2, Rev. 0140 210 75 75 NS 85 90

Average 241 112 122 7781 100

Minimum 214 98 94 7059 100Results

All HeatAverage

241 100


11/12


Figure 4 Overview of the Westpath project,

June to October 2002

Existing

Pipeline

First installation World wide

X100, 1000 m

NPS 48

Standard Technology

X80 20900 m

NPS 48

Figure 5 Schematic of Saratoga Project

300 400 500 600 700 800 900

Rt0.5on transverse ro nd ar specimen, MPa

300

400

500

600

700

800

900

Rt0.5

ontransverseflattened

re

ctangularspecimen,

MPa

GRS 550, X80GRS 550, X80

X70X70

X60X60

X52X52

- UOE manufactured pipe- UOE manufactured pipe- HFI welded pipe- HFI welded pipe

- SWP spiral weld pipe- SWP spiral weld pipe

- Hot rolled seamless pipe- Hot rolled seamless pipe

X100X100

HFIHFIHRSHRS

SWPSWP

Rt0.5- transverseRt0.5- transverseflattened strip - round barflattened strip - round bar

UOEUOE

x = yx = y

EPRG28VP3R Figure 6 Comparison of the yield strength values measured on

flattened strap rectangular specimens with thosemeasured on transverse round bar specimens for

different pipe types(from G. Knauf and J. Spiekout, 2002)

Figure 7 Internal welding on Grade 690, standard short circuit

Figure 8 External fill passes on Grade 690using pulsed GMAW procedures


12/12


Figure 9 Pipe layout after all field bending had been completed

Figure 10 Typical coating and marking for the Grade 690 pipe

EA

P

P

EA

Stress

St

yield

stress

ultimate

stress

yield

strain

failure

strain

EA EA

(a) (b)

(c)Figure 11 Schematic of load and displacement controlled event

(a) (b)Figure 12 (a) Bulging mode buckling at high internal pressure

and (b) Diamond mode buckling at zero or low pressure

Hydraulic simulation to

predict temperature profile

over the design life

Geothermal analysis to

predict frost heave over

the design span at all

identified sites

Structural (pipe-soil

interaction) analysis to

predict stress and strain

Establish tensile strain limit

based on material property,

welding and inspection

Establish compressive

strain limit based on

material property, pipe

geometry and pressure

Design criteria based on

strain limits

Reliability based design methodology to ensure the target

reliability levels are met

Figure 13 Overall Design Approach for Frost Heave

and Thaw Settlement

Documents

Design, Application and Installation of an X100 Pipeline.pdf