weld code revision progress report

8/10/2019 Weld Code Revision Progress Report

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DRAFT

A Comprehens ive Update in the Evaluation of PipelineWeld Defects

U.S. DOT Agreement No. DTRS56-03-T-0008

PRCI Contact No. PR-276-04503

Authors:

Yong-Yi Wang and Ming Liu

Engineering Mechanics Corporation of Columbus3518 Riverside Dr., Suite 202

Columbus, OH 43221

Publication Date:November 2004

For internal circulation within PRCI, DOT, and API


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Table of Contents List of Figures .................................................................................................................................................vExecutive Summary..................................................................................................................................... viii1.0 Introduction..........................................................................................................................................1

1.1 Background ...........................................................................................................................11.2 Scope.....................................................................................................................................21.3 Structure of the Defect Assessment Procedures....................................................................21.4 Terminology and Notation ....................................................................................................3

1.4.1 Pipe Properties....................................................................................................................31.4.2 Girth Weld Properties .........................................................................................................31.4.3 Applied Loads.....................................................................................................................31.4.4 Defect Dimensions..............................................................................................................3

2.0 Level 1 Assessment Procedures...........................................................................................................42.1 Overview...............................................................................................................................42.2 Level 1 Option 1 Assessment................................................................................................4

2.2.1 Additional Requirements ....................................................................................................42.2.2 Acceptance Criteria.............................................................................................................52.2.3 Computation of the Load Level P r .....................................................................................7

2.3 Level 1 Option 2 Assessment................................................................................................82.3.1 Overview.............................................................................................................................82.3.2 Additional Requirements ....................................................................................................82.3.3 Determination of the Key Components in the FAD Procedure ........................................102.3.4 Defect Acceptance Criteria...............................................................................................11

2.4 Limitations of the Level 1 Procedures ................................................................................123.0 Level 2 Assessment Procedures.........................................................................................................134.0 References..........................................................................................................................................14Appendix A Validation of the Assessment Procedures against Full-Scale Bend Tests ............................ A-1

A.1 Background ...................................................................................................................... A-2A.2 Experimental Database for Validation ............................................................................. A-2A.3 Validation Process............................................................................................................ A-3A.4 Results of the Validation.................................................................................................. A-3A.5 Observation from the Validation against Full-scale Bend Tests ...................................... A-4A.6 References........................................................................................................................ A-7

Appendix B Validation of the Assessment Procedures against Curved Wide Plate Tests .........................B-1B.1 Background .......................................................................................................................B-2B.2 Overview of the Wide Plate Tests.....................................................................................B-2B.3 Validation Process.............................................................................................................B-2B.4 Validation Results against Curved Wide Plate Test Data .................................................B-3B.5 Observation from the Validation against Curved Wide Plate Test Data...........................B-3B.6 References.........................................................................................................................B-7

Appendix C Stress Intensity Factor Solution .............................................................................................C-1C.1 Background .......................................................................................................................C-2C.2 Parametric Equations.........................................................................................................C-3C.3 Comparison between Fitted Equations and the FE Results...............................................C-3C.4 References.........................................................................................................................C-5

Appendix D Plastic Collapse Solution...................................................................................................... D-1D.1 Background ...................................................................................................................... D-2D.2 New Defect Size Correction Factor ................................................................................. D-2D.3 Comparison with Full-scale Test Data ............................................................................. D-3D.4 References........................................................................................................................ D-4

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Appendix E Estimation of Applied Stress from Applied Strain.................................................................E-1E.1 Assumed Stress Strain Relations.......................................................................................E-2E.2 Estimation of Strain Hardening Exponent ........................................................................E-2E.3 Estimation of Y /T Ratio from Pipe Grade or Yield Stress.................................................E-2E.4 Estimation of Uniform Strain............................................................................................E-4E.5 References.........................................................................................................................E-4

Appendix F Incorporation of Weld Strength Mismatch.............................................................................F-1F.1 Background .......................................................................................................................F-2F.2 Determination of Weld Width for Girth Weld ..................................................................F-2F.3 Suggested Approach for the Treatment of Weld Strength Mismatch ............................... F-3F.4 References.........................................................................................................................F-3

Appendix G Example Problem for a Level 1 Option 2 Assessment ......................................................... G-1G.1 Background ...................................................................................................................... G-2G.2 Input Data......................................................................................................................... G-2G.3 Steps to Derive the Defect Acceptance Level .................................................................. G-2G.4 Comments and Observations............................................................................................ G-5

Appendix H Comparison of Acceptance Criteria...................................................................................... H-1H.1 Background ...................................................................................................................... H-2H.2 Comparison of Acceptance Criteria ................................................................................. H-2

Appendix I Limits of Applicability of the Current API 1104 Appendix A Acceptance Criteria ................ I-1I.1 Background of API 1104 Appendix A ...................................................................................I-2I.2 Appendix A from the Perspective of the Code Structure .......................................................I-2I.3 Limits of Applicability from Analytical and Experimental Work Funded by API ................ I-3I.4 Limits of Applicability from 1980s Work Funded by DOT..................................................I-4I.5 Observation from Historical and More Recent Work............................................................. I-6I.6 Limits of Applicability of the Current API 1104 Appendix A Acceptance Criteria .............. I-7I.7 Recommendation about the Limits of Applicability of API 1104 Appendix A ..................... I-7I.8 References .............................................................................................................................. I-9

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List of Figures

Figure 1-1 Dimension of a pipe with a surface-breaking defect.........................................3

Figure 2-1 Level 1 Option 1 defect acceptance level at various applied loadlevels for CTOD toughness equal to or greater than 0.25 mm (0.010

inch) ..................................................................................................................6Figure 2-2 Level 1 Option 1 defect acceptance level at various applied load

levels for CTOD equal to or greater than 0.10 mm (0.004 inch) andless than 0.25 mm (0.010 inch).........................................................................6

Figure 2-3 Relation between Y /T ratio and pipe grade of Eq. (1) .....................................7

Figure 2-4 Schematic overview of the Level 1 Option 2 procedure ..................................9

Figure A-1 Full-scale test data plotted on the FAD of the Level 1 Option 2 procedure. The nominal SMYS were used as the strength input................ A-5

Figure A-2 Full-scale test data plotted on the FAD of the Level 1 Option 2 procedure. The measured yield stresses were used as the strengthinput. ............................................................................................................ A-5

Figure A-3 Full-scale test data that fall within the defect size and CTODlimitations plotted on the FAD of the Level 1 Option 2 procedure.The nominal SMYS were used as the strength input................................... A-6

Figure A-4 Full-scale test data that fall within the defect size and CTODlimitations plotted on the FAD of the Level 1 Option 2 procedure.The measured yield stresses were used as the strength input. ..................... A-6

Figure B-1 Curved wide plate test data plotted on the FAD of the Level 1 Option2 procedure. The nominal SMYS were used as the pipe strengthinput. .............................................................................................................B-4

Figure B-2 Curved wide plate test data plotted on the FAD of the Level 1 Option2 procedure. The measured yield and tensile strength of the pipe wereused as the pipe strength input......................................................................B-5

Figure B-3 Curved wide plate test data plotted on the FAD of the procedure thatis an extension of the Level 1 Option 2 procedure. The measuredyield and tensile strength of the pipe AND weld were used as thestrength input. ...............................................................................................B-5

Figure C-1 Comparison of the fitted equations as a function of defect depth ratio ........C-2

Figure C-2 Comparison of the fitted curves with the original data of Chapuloit for pipes with D/t of 42. The symbols are from the original data and thecurves are from the fitted equations. ............................................................C-4


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Figure D-1 Comparison of the Miller plastic collapse solution and the full-scaletest data. The prior and current defect size correction lines are shown...... D-3

Figure E-1 Comparison of linepipe longitudinal test data with the Webster andBannister correlation equations [2]...............................................................E-3

Figure E-2 Comparison of the relations between Y /T ratio and pipe grades fromestimation equations and codes ....................................................................E-3

Figure F-1 Determination of weld width 2H for a typical girth weld geometry ............ F-2

Figure G-1 Defect acceptance curve from the example problem with the Level 1Option 2 procedure ...................................................................................... G-6

Figure G-2 Illustration of the critical points on the failure assessment curve fromthe example problem. Points 8 and 9 are on the cut-off line, thereforethe acceptable defect sizes for those points are toughnessindependent. ................................................................................................. G-6

Figure G-3 The upper right corner of Figure G-2 .......................................................... G-7

Figure H-1 Comparison of the defect acceptance levels from API 1104 AppendixA and those of the current procedures with no safety factor on theallowable defect length ................................................................................ H-4

Figure H-2 Comparison of the defect acceptance levels from API 1104 AppendixA and those of the current Level 1 procedures with the recommendedsafety factor on the allowable defect length ................................................ H-4

Figure H-3 Comparison of the defect acceptance levels from API 1104 Appendix

A and those of the current Level 1 procedures with the recommendedsafety factor on the allowable defect length ................................................ H-5

Figure H-4 Comparison of the defect acceptance levels from the current Level 1Option 1 and Option 2 ................................................................................. H-5

Figure H-5 Comparison of the defect acceptance levels from API 1104 AppendixA and those of the current procedures with no safety factor on theallowable defect length ................................................................................ H-6



Figure H-8 Comparison of the defect acceptance levels from the current Level 1Option 1 and Option 2 ................................................................................. H-7

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Figure I-1 Comparison of allowable flaw size between API 1104 Appendix Aand the NBS criteria with an assumed CTOD toughness of 0.005 inch(0.127 mm) .................................................................................................... I-5

Figure I-2 Comparison of allowable flaw size between API 1104 Appendix Aand the NBS criteria with an assumed CTOD toughness of 0.010 inch

(0.254 mm) .................................................................................................... I-5Figure I-3 Comparison of allowable defect size among various codes and

procedures...................................................................................................... I-6

Figure I-4 Comparison of the defect acceptance criteria from the current plasticcollapse solution with no safety factor and those of API 1104Appendix A....................................................................................................I-8

Figure I-5 Comparison of the defect acceptance criteria from the current plasticcollapse solution with a safety factor of 1.5 on the defect length andthose of API 1104 Appendix A ..................................................................... I-9

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A Comprehensive Update in the Evaluation of Pipeline WeldDefects

Executive Summary

Girth weld defect acceptance criteria are set and enforced in all pipeline constructions

in the U.S. per federal regulations (CFR 49 Parts 192 and 195). With the increased use ofmechanized welding and AUT (Automated Ultrasonic Testing) in new pipelineconstructions, alternative defect acceptance criteria based on ECA (Engineering CriticalAssessment) principles are frequently used in lieu of the traditional workmanship criteria.The alternative defect acceptance criteria in the current Appendix A of API 1104 haveremained largely unchanged since its introduction in the early 1980s. In the meantime,the characteristics of the linepipe materials, welding processes, and construction practicehave evolved since the adoption of the code. The recent surge in the use of mechanizedwelding/AUT/ECA created a mismatch between the new materials/welding processes andthe outdated alternative defect acceptance criteria. Looking ahead, the trend in pipeline

construction is moving towards larger diameter and higher strength linepipes, such asX80, X100, and even X120. The characteristic of these ultra-high strength materials andtheir welding processes make the use of the current Appendix A highly questionable.

This report presents the girth weld defect assessment procedures for stress- based design. The major components of this report are (1) technical basis for thedevelopment of the revised girth weld defect acceptance criteria, (2) validation of theacceptance criteria against experimental test data, and (3) recommended structure for therevision of API 1104 Appendix A. The main body of the report is written in such a waythat it can be easily turned into code language. The supporting data, both analytical andexperimental, are given in the appendices. Examples are given to show the use of thenew assessment procedures. Comparisons in defect acceptance criteria are made betweenthe new procedures and the current API 1104 Appendix A.

The new proposed procedures have two options. Option 1 is given as an easy to usegraphical approach, whereby allowable flaw dimensions can be determined on the basisof a somewhat more restrictive minimum toughness level. Option 2 provides moreflexibility and generally allows larger flaws, at the expense of more complicatedcalculations.

In comparison to the current API 1104 Appendix A, the major advantages of thenewly proposed procedures are:

Consistent level of conservatism

Inclusion of both plastic collapse and fracture criteria. The current API 1104Appendix A includes only fracture criterion. The acceptance criteria are easier to use for the most frequently occurring defects

in modern pipeline construction. Reduced minimum CTOD toughness requirements, accompanied by tighter defect

tolerance, allows wider application of the alternative acceptance criteria.

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1.0 Introduction

1.1 Background

Girth welds made in field welding conditions often contain some imperfections. These

imperfections are sometimes referred to as defects. Many of these defects are a naturaloccurrence of the field welding processes. Traditionally, the tolerable defect sizes are set byworkmanship-based criteria. One of the earliest and perhaps the most widely recognizedworkmanship criteria is that given in the main body of API Standard 1104 [ 1]. These criteriaare empirically-based and historically proven safe in practice. In most cases, they are notquantitatively related to the severity of the defects in safely maintaining the operation of the

pipelines.

Beginning in the late 1970s and early 1980s, alternative defect acceptance criteriahave been implemented in various codes and standards. These criteria are based on fracturemechanics principles. They relate the tolerable defect size with the magnitude of loading in

pipelines and materials resistance to failure. When correctly used, these criteria allowengineers to assess the suitability of the pipelines containing the defects for intended serviceconditions, or fitness-for-service (FFS) . Assessment based on the FFS principles isalternatively referred to as Engineering Critical Assessment, or ECA. The ECA codes thatare most frequently used in the North American pipeline industry are API 1104 Appendix A[1], CSA Z662 Appendix K [ 2], and BS7910:1999 [ 3]. Although certain parts of API 1104Appendix A and CSA Z662 Appendix K had their root in PD6493:1980 [ 4], the defectacceptance criteria vary significantly. The PD 6493:1980 was succeeded by PD 6493:1991[5] and more recently by BS 7910:1999. A more complete review of the evolution of

pipeline ECA procedures is given in Reference [ 6].

This document takes advantage of the significant progress made in understanding thegirth weld behavior over the last two decades. Significantly, the following elements form the basis of this document.

Historical and recent experimental data, from small specimen to full-scale tests,

Fundamental fracture mechanics principles as implemented in weld defect assessment procedures for engineering structures,

Recently published and/or updated pipeline codes around the world, such as EPRGguidelines [ 7], Australian Standard AS2885 [ 8], API RP 579 [ 9], CSA Z662 2003Edition [ 2], etc.

State-of-art research in weld defect assessment, such as the SINTAP procedure [ 10] and the PRCI GWIS procedure [ 11,12 ].

This document presents procedures for the assessment of defects in transmission pipelinegirth welds. The assessment procedures are simplified, whenever possible, to address the

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specific needs of this industry without sacrificing the necessary consistency and accuracy ofthe procedures.

Unless otherwise specified, the defects or imperfections here refer to planar defects.

1.2 Scope

This use of these assessment procedures is restricted to the following conditions:

Girth welds between pipes of equal wall thickness

No onerous fatigue crack growth in construction and under service conditions

No sub-critical crack growth, such as creep and environmentally-assisted crackgrowth

No dynamic loading

1.3 Structure of the Defect Assessment Procedures

The assessment procedures is structured in two levels. Level 1 is for stress-based designand Level 2 is for strain-based design. There are two options in each level. Option 1 is thesimplified procedure. Option 2 allows for broader applications than Option 1, but at theexpense of more complex computation and/or more required input data. The majorcharacteristics of the assessment procedures are given in Table 1.

Table 1 Structure of the Proposed Assessment Procedures

DiameterGrade and

Tensile PropertyLongitudinal

Load

1

Plastic collapsecriterion, corrected

by the Option 2 procedure

Graphical format. Minimalcalculation required.

2

Failure assessmentdiagram (FAD)format. Extensivelyupdated from thePRCI GWIS

procedure

Allow the assessment of brittlefracture, plastic collapse, andthe interaction of the twofailure modes in a singleconsistent format. Ability toaccommodate new features,such as weld strength mismatch,welds between pipes of unequalwall thickness, if desired.

1 Current work Graphical or tabular format thatcovers majority of applications

2 Current work Complex multi-variable format,may require computationalsoftware for easy application

Feature

No limit1

2 No limit

Range of Applicabili ty

TBD

Applied stress SMYS.

Applied strain 0.50%.

Applied strain> 0.5%

A s s e s s m e n

t

L e v e l

Basis O p

t i o n

Test data availableup to X100

2


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1.4 Terminology and Notation

1.4.1 Pipe Properties D = pipe outer diameter, inch or mm

R = pipe outer radius, R D/2, inch or mm

t = pipe wall thickness, inch or mm

= pipe diameter to wall thickness ratio, D/t

y , Y = specified minimum yield stress of the pipe material, or SMYS, ksi or MPa

t , T = ultimate tensile strength of the pipe material, or UTS, ksi or MPa

f = flow stress of the pipe material, f = ( y+ t )/2, ksi or MPa

E = Youngs modulus

= Poissons ratio

1.4.2 Girth Weld Properties

1.4.3 Applied Loads

a = applied longitudinal stress, ksi or MPa

P r = normalized applied stress or load level, P r a / f

1.4.4 Defect Dimensionsa = defect depth, inch or mm

c = defect half length, inch or mm

= ratio of defect length to pipe circumference, c/ R = 2 c/ D,

= defect height to crack-depth ratio, a/t

a

2c

a

2c

Figure 1-1 Dimension of a pipe with a surface-breaking defect

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2.0 Level 1 Assessment Procedures

2.1 Overview

The Level 1 assessment procedures represent the state-of-art understanding in the

assessment of the significance of pipeline girth weld defects under stress-based design,normally defined as applied longitudinal strain less than 0.5% and applied longitudinal stressless than the specified minimum yield stress of the pipe material. There are two options atthis assessment level.

Option 1 is a simplified approach in graphical format. It relies on theoretically sound andexperimentally validated plastic collapse criterion when the fracture toughness is sufficientlyhigh. The criterion is modified by the Option 2 approach when the fracture toughness islower, but sufficiently high to avoid brittle fracture. The Option 1 approach is based on the

premises that modern pipeline steels joined using modern welding procedures andconsumables usually produce girth welds with good toughness. Consequently, brittle

fracture is usually not a concern. The defect acceptance level can be derived from a suitable plastic collapse criterion, provided that certain minimum toughness requirements are met. Anotable example of this philosophy is the EPRG Guideline [ 7].

Option 2 is in the form of a failure assessment diagram, or FAD, which was first proposed in the mid-1970s [ 13]. The FAD format has become by far the most widely useddefect assessment procedure for a wide range of industries, from the petroleum refiningindustry (API RP 579 [ 9]) to the nuclear power generation industry (R6 [ 14] and ASMESection XI [ 15]). The FAD format allows the simultaneous consideration of brittle fracture,

plastic collapse, and the interaction between those two failure modes (elastic-plasticfracture). The FAD approach is considerably more complex in computation. Furthermore,

some proficiency and understanding of fracture mechanics is necessary to ensure the procedure is applied correctly. However, validated computer programs, either fromcommercial market or developed internally, should greatly facilitate the assessment process.

2.2 Level 1 Option 1 Assessment

2.2.1 Additional Requirements

In addition to the requirements of Section 1.2, the following requirements are necessaryat the minimum design temperature.

1. Weld metal strength even- or over-matches that of pipe material

2. No failure in the HAZ (heat-affect-zone) when defect-free welds are tested3. Applied longitudinal stress no greater than SMYS and the applied longitudinal strain

no greater than 0.5%

4. The minimum CTOD toughness no less than 0.10 mm (0.004 inch)

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5. The minimum and averaged Charpy values are greater than 30 J and 40 J,respectively.

The requirements of 1 and 2 are considered met if the cross-weld API tensile specimensdo not break in the weld or HAZ. The weld reinforcement on both sides of the specimenshall be removed for such tests.

2.2.2 Acceptance Criteria

Two sets of acceptance criteria are given, depending on the fracture toughness of thematerials.

When the CTOD toughness is equal to or greater than approximately 0.25 mm (0.010inch), the critical defect size is largely independent of toughness value. The defectacceptance level is given in Figure 2-1 at various levels ( P r ). This acceptance level isderived from the plastic collapse criteria given in Appendix D, with a safety factor of 1.5 onthe defect length. If a load level is not given in Figure 2-1, the acceptance level can beobtained by interpolating the adjacent curves or by taking the value of the next higher loadlevel.

At a CTOD toughness equal to or greater than 0.10 mm (0.004 inch) and less than 0.25mm (0.010 inch), the critical defect size is dependent on toughness values for deep defects,

but fully plastic-collapse-controlled for shallow defects. Some examples of this defect depthdependence are shown in Appendix H. The defect acceptance level given in Figure 2-2 iscalibrated to a CTOD toughness level of 0.10 mm (0.004 inch). The safety factor on thedefect length is approximately 1.5 at the toughness level of 0.10 (0.004 inch), but higher athigher toughness levels.

The total defect length shall be no greater than 12.5% of the pipe circumference. The

maximum defect height shall be no greater than 50% of the pipe wall thickness.

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0.0

0.1

0.2

0.3

0.4

0.5

0.000 0.025 0.050 0.075 0.100 0.125 Allowable Length / Pipe Circumference

A l l o w a b

l e H e i g

h t / P i p e W

. T .

0.7250.750

0.775

0.800

0.825

0.8500.875

0.900

0.925

0.9500.975

P r =0.700

Figure 2-1 Level 1 Option 1 defect acceptance level at various applied load levels for

CTOD toughness equal to or greater than 0.25 mm (0.010 inch)

0.0

0.1

0.2

0.3

0.4

0.5

0.000 0.025 0.050 0.075 0.100 0.125 Allowable Length / Pipe Circumference

A l l o w a b

l e H e i g h

t / P i p e W

. T .

P r =0.725

0.7500.775

0.8000.825

0.8500.875

0.9000.925

0.9500.975

0.700

0.5500.6750.650

0.625

0.600

0.575

Figure 2-2 Level 1 Option 1 defect acceptance level at various applied load levels for

CTOD equal to or greater than 0.10 mm (0.004 inch) and less than 0.25 mm(0.010 inch)

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2.2.3 Computation of the Load Level P r

In accordance with the definition given in Section 1.4.3, it is necessary to determinematerials flow stress in order to obtain the load level P r . The yield to tensile ( Y /T ) ratio ofthe pipe material for a given grade is estimated as,

25.2

75.2121

1/

+

=

y

T Y

, (1)

where the pipe grade, , is in the unit of ksi . Alternatively, the Y /T ratio may be obtained

from Figure 2-3. The background of the Y /T ratio and pipe grade relation is given inAppendix E.

y

The flow stress is therefore computed as,

+= T Y y f /1

15.0 , (2)

The load level, P r , is given as,

f

ar P

= . (3)

The applied longitudinal stress, a, is obtained from stress analysis.

0.7

0.8

0.9

1.0

50 60 70 80 90 100 110 120

Grade (ksi)

Y / T

Figure 2-3 Relation between Y /T ratio and pipe grade of Eq. (1)

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2.3 Level 1 Option 2 Assessment

2.3.1 Overview

There are three key components in the defect assessment in FAD format, see Figure 2-4:

1. Failure assessment curve (FAC),2. Stress or load ratio, S r or Lr , and3. Toughness ratio, K r .

The FAC is a locus that defines the critical states in terms of the stress and toughnessratios. The stress ratio defines the likelihood of plastic collapse. The toughness ratio is theratio of applied crack driving force over the materials fracture toughness. It defines thelikelihood of brittle fracture.

The exact form of FAC and the computation of stress and toughness ratios depend on thetype of structural geometry, defect location, defect size, and materials strain hardening

behavior. Over the years, many solutions have been developed for various structuralgeometries, defect locations, and material properties. The assessment procedures presentedhere is specifically developed and validated for pipeline girth welds.

The defect assessment in the FAD format may be used in one of two ways:

1. For a structure with a known defect and applied load level, the significance ofthe defect, i.e., safe or unsafe, can be determined. This is done by comparingthe location of the assessment point with the FAC. If the point falls insidethe FAC locus, the structure is deemed safe. Figure 2-4 shows how this typeof assessment is done.

2. For a structure with known defect location, material property, and applied

load level, the critical defect size can be determined. This is almost alwaysdone iteratively, and therefore can be time-consuming without the aid of acomputer program.

2.3.2 Additional Requirements

In addition to the requirements of Section 1.2, the following requirements are necessaryat the minimum design temperature.

1. Weld metal strength even- or over-matches that of pipe material

2. No failure in the HAZ (heat-affect-zone) when defect-free welds are tested

3. Applies longitudinal stress no greater than SMYS and applied longitudinal strain no

greater than 0.5%4. The minimum CTOD toughness is greater than 0.05 mm.

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0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Lr

Kr

Plastic Collapse

Brittle FractureFailure Assessment

Curve, Eq. (4)

Unacceptable Region

Acceptable Region

Assessment

Point

y

e

ne

J d

= , Eq. (7)

d n, Eqs. (8), (9), (10), and (1)

J e, Eqs. (11), (12), and (13)

mat

er K

= , Eq. (6) mat , CTOD toughness

a, stress analysis

c

ar L

= , Eq. (14) c, Eq. (15)

Cutoff, Eq. (5)

Figure 2-4 Schematic overview of the Level 1 Option 2 procedure

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2.3.3 Determination of the Key Components in the FAD Procedure

2.3.3.1 Failure Assessment Curve (FAC)

The FAC is taken from R6 Option 1 [ 14],

( ) ( )[ ]62 65.0exp7.03.0)14.01(r r r r

L L L f K +== (4)

The cut-off of the FAC on the Lr axis is at,

y f cutoff r L /= , (5)

where f is determined by Eq. (2).

2.3.3.2 Assessment Point, Toughness Ratio K r

When materials fracture toughness is measured in CTOD, K r is given as,

mat

er K

= (6)

where mat is the CTOD toughness of the material. The elastic component of the CTODdriving force, e, may be computed as,

y

ene

J d

= (7)

The J to CTOD conversion factor, d n, is given as,

882.01

19.31

69.32

+

=

nnd n

( )( ){ }

(8)

T Y n t

//1ln005.0/ln =

22.0*00175.0

, (9)

, (10)+= yt

where the pipe grade, , is in the unit of ksi . The elastic J integral is given as, y

( )22

1/ =

E K

J I e (11)

ba I F a K = (12)

The parameter F b is a function of pipe diameter ratio, , and defect length , and defectheight ,

( ) 2806.01983.0906.0791.031.209.1,, mm

F b +++= (13a)

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21 345.0163.000985.0 =m (13b)

22 155.018.200416.0 +=m (13c)

Additional corrections apply to F b for the following defect conditions,

( ) == ,80,,, bb F F if ,1.0 and , 80> (13d)

, .

1080>( )

==

,

1.080,,, bb F F if ,1.0


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the assessment falls on the failure assessment curve. This represents anothercritical state with a shallower and longer defect than that determined in (a).Make a note of the defect height and length.

(c) Repeat the process (b) until the shallowest defect height of interest hasreached.

4. If the assessment point falls outside the safe region,

(a) Decrease the defect length until the assessment point falls on thefailure assessment curve. This represents a critical state with thecombination of load, material property, and defect size. Make a noteof the defect height and length.

(b) Repeat the steps 3(b) and 3(c).

An example of the procedure is given in Appendix G.

2.4 Limitations of the Level 1 Procedures

Due to the availability of public domain data, the validations of the procedures have been primarily limited to large diameter and large D/t ratio pipes. The fundamental basis of theassessment procedures does not place limits on diameter or D/t ratio. It is prudent, however,that cautions be exercised in applying the procedures to heavy wall and small diameter pipes.

The effects of residual stress are not explicitly considered. It is believed that the residualstress has minimal effects on the defect acceptance criteria provided that (1) the failuremechanism is not time-dependent and (2) the CTOD toughness is greater than the minimumrequired value of 0.05 mm (0.002 inch). The examples of time-dependent failuremechanisms include, but not limited to, fatigue and stress corrosion cracking.

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3.0 Level 2 Assessment Procedures

The part is under development.

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4.0 References

1 API Standard 1104, "Welding of Pipelines and Related Facilities," 19th Edition, September1999.

2 Canadian Standards Association, CSA-Z662, "Oil and Gas Pipeline Systems," 2003.

3 British Standard Institute, BS7910, Guidance on methods for assessing the acceptability offlaws in structures, 1999.

4 British Standard Institution, PD6493:1980, Guidance on Some Methods for the Derivation ofAcceptance Levels for Defects in Fusion Welded Joints.

5 British Standard Institution, PD6493:1991, Guidance on Some Methods for the Derivation ofAcceptance Levels for Defects in Fusion Welded Joints.

6 Wang, Y.-Y., Swatzel, J., Horsley, D., and Glover, A., Girth Weld ECA from the Perspectiveof Code Revisions in North America, Proceedings of the International Pipeline Conference2002 , Calgary, Alberta, Canada, September 29-October 3, 2002.

7 Knauf, G. and Hopkins, P., EPRG Guidelines on the Assessment of Defects in TransmissionPipeline Girth Welds, Sonderdruck aus 3R International, 35 Jahrgang, Heft 10-11/1996, s.620-624.

8 Australian Standard, AS 2885.2-1995, Pipelines Gas and Liquid Petroleum, Part 2:Welding.

9 API RP 579, Fitness-for-Service, First Edition, January 2002.

10 SINTAP Procedure, Final Version, November 1999.

11 Wang, Y.-Y., Rudland, D., Horsley, D., Development of a FAD-Based Girth Weld ECAProcedure, Part I Theoretical Framework, Proceedings of the 4 th International PipelineConference, Calgary, Alberta, Canada, September 29-October 3, 2002.

12 Wang, Y.-Y., Rudland, D., Horsley, D., Development of a FAD-Based Girth Weld ECAProcedure, Part II Experimental Verification, Proceedings of the 4 th International PipelineConference, Calgary, Alberta, Canada, September 29-October 3, 2002.

13 Harrison, R. P., Loosemore, K., and Milne, I., Assessment of the Integrity of StructuresContaining Defects, CEGB Report No. R/H/6, Central Electricity Generating Board, UnitedKinddom, 1976.

14 British Energy Generation Ltd., Assessment of Integrity of Structures Containing Defects,R/H/R6-Revision 3, 1999.

15 ASME Boiler and Pressure Vessel Code, Section XI, Appendix H, 1992 Edition, July 1992.

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Appendix A Validation of the Assessment Procedures against Full-ScaleBend Tests

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A.1 Background

This appendix provides the validation of the Level 1 Option 2 procedures. Since the plastic collapse criterion implemented in the Level 1 Option 1 procedure is a part of theOption 2 procedure, this validation is also an indirect confirmation of the Option 1

procedure.The Level 1 Option 2 procedure is substantially taken from the PRCI-funded work of

Wang, et al. [ 1,2 ]. This document incorporates several improvements made to the initialwork. They include:

Slightly revised plastic collapse criterion,

Updated stress intensity factor solutions,

Updated Y /T ratio estimation from pipe grade,

Updated estimation of strain hardening exponent, and

Revised conversion factor from J -integral to CTOD.

These improvements represent incremental advances to the initial work. The outcome ofthis validation was not expected to be significantly different from that of the initialvalidation. Nevertheless, this validation is the direct confirmation of the exact proceduresoutlined in this document.

A.2 Experimental Database for Validation

Data from 69 full-scale experimental tests were collected and used as the basis for thisvalidation. All the tests were conducted in bending with artificially introduced defects in the

circumferential direction, simulating girth weld defects. These 69 tests represent perhaps thelargest test database for large diameter pipelines in the open literature. Among these tests, 54tests came from full-scale experimental tests conducted at the Welding Institute of Canada(WIC) and the University of Waterloo [ 3,4 ]. Most of the tested pipes were API Grade X70(483 MPa), a few were X65 (448 MPa) and X60 (414 MPa) grades. The pipe diameterranged from 20 inch (508 mm) to 42 inch (1067 mm). The reported CTOD toughness was inthe range of 0.03 to 0.10 mm (0.0012 to 0.0039 inch). The bending moments, stresses, andremote nominal strains at the critical events were reported for many of these tests. Thecritical events could be brittle fracture, brittle fracture after ductile tearing, buckling, ormanual intervention.

In addition to the WIC and University of Waterloo tests, four tests by Erdogan [ 5] areincluded in the test database. These tests were conducted on X60 pipes with 20 inch OD and0.344 inch (8.74 mm) wall thickness. The reported CTODs were 0.554 mm. The other testdata include 8 tests by Hopkins on X65 36 inch (914.4 mm) OD pipe [ 6] and 3 tests byWilkowski on X60 30 inch (762 mm) OD pipes [ 7]. The CTOD toughness of the Hopkinsand Wilkowski tests were in the range of 0.02 to 0.10 mm.

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A.3 Validation Process

For each test, 7 parameters were entered into the assessment procedure,

1. Pipe diameter,

2. Pipe wall thickness,

3. Pipe grade or measured yield stress

4. Defect depth,

5. Defect length,

6. CTOD toughness, and

7. Magnitude of the applied stress.

An assessment point is produced for each test, following the procedure outlined inSection 2.3.3. The relative conservatism and accuracy of the assessment procedure isdetermined by examining the location of the assessment points. A computer program wasdeveloped to facilitate the calculations.

A.4 Results of the Validation

The assessment points of all 69 full-scale tests are plotted on the FAD in Figure A-1 andFigure A-2. The nominal pipe grades are used as the pipe strength input in Figure A-1, whereas the measured yield stresses are used as the pipe strength input in Figure A-2. Inreference to Eq. (5), the cut-off for the FAC varies by pipe grade (pipe strength). The cut-offfor a nominal X70 pipe is shown in the figures. The cut-off points for the entire databasevary slight as the grades are in the narrow range of X60 to X70.

Since the assessment points represent actual failure events, points falling outside of the

FAC mean the FAC is conservative with respect to the actual failure events. Conservative predictions are obtained for all tests. When the nominal yield strength is used, the medianvalue of the safety factor in stress is 1.66 with a standard deviation of 0.37. The safety factoris the ratio of the experimentally measured maximum stress over the predicted failure stress,with the material property and defect size remaining the same. The median value of thesafety factor in stress is 1.51 with a standard deviation of 0.35 when the measured yieldstresses of the pipes were used as the pipe strength input.

The database of 69 full-scale tests include defects from as shallow as 6% of the wallthickness to as deep as through-wall defects. The CTOD toughness ranges from 0.02 mm to0.55 mm. In reference to Section 2.3.4, the tests that are directly relevant to the acceptance

criteria are those with defects less than 50% of pipe wall thickness and CTOD toughnessgreater than 0.05 mm. The maximum defect length in the database is 12% of the pipecircumference, therefore all within the acceptance limits. When the maximum defect sizeand the minimum CTOD toughness criteria of Section 2.3.4 are applied, 35 tests fall withinthe limits, or about one-half of the total number of tests.

The assessment points of these 35 full-scale tests are plotted on the FAD in Figure A-3and Figure A-4. The nominal pipe grades are used as the pipe strength input in Figure A-3,

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whereas the measured yield stresses are used as the pipe strength input in Figure A-4. Incomparison, the scatter of the test data with respect to the FAC is markedly reduced when thelimits of Section 2.3.4 are applied. When the nominal yield strength is used, the medianvalue of the safety factor in stress is 1.46 with a standard deviation of 0.28. The medianvalue of the safety factor in stress is 1.44 with a standard deviation of 0.23 when the

measured yield stresses of the pipes were used as the pipe strength input.

A.5 Observation from the Validation against Full-scale Bend Tests

1. The assessment procedure is conservative when compared to all 69 full-scale testdata. The database contains tests with defect size and CTOD toughness outsidethe limits of the current acceptance criteria. This demonstrates the robustness ofthe assessment procedure.

2. When the limitations on defect size and CTOD toughness, as proposed in therecommended acceptance criteria, are applied, the consistency of the assessment

procedure shows marked improvement with respect to the test data.

3. It should be noted that no safety factor was applied when the assessment procedure is validated against the experimental test data. The assessment procedure is assumed to predict critical failure events. In the recommendedacceptance criteria, a safety factor of 1.5 is applied after the critical defect sizeis determined. This safety factor in defect length is in line with historicalrecommendations. A higher degree of conservatism than that shown here is

preserved when the recommended acceptance criteria are applied.

4. The scatter in the test data with respect to the FAC is perhaps due to the fact that anumber of factors affecting the test results cannot be reconstructed from the

published papers and reports. These factors include, but not limited to, weld

strength mismatch, scatter in CTOD toughness, variation in stress-strain curves ofthe pipe material and weld metal, etc. It is believed that, for instance, the reportedCTOD toughness is the minimum value of a batch of tests. It may or may notreflect the CTOD toughness on a specific piece of pipe at the specific defectlocation. On the other hand, such details are frequently not available if theassessment procedure is applied to existing pipelines. This validation shows thatthe procedure is conservative, but not overly so, when used with minimumrequired input data.

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0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0L r

K r

Figure A-1 Full-scale test data plotted on the FAD of the Level 1 Option 2 procedure.

The nominal SMYS were used as the strength input.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0L r

K r

Figure A-2 Full-scale test data plotted on the FAD of the Level 1 Option 2 procedure.

The measured yield stresses were used as the strength input.

A-5


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0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0L r

K r

Figure A-3 Full-scale test data that fall within the defect size and CTOD limitations

plotted on the FAD of the Level 1 Option 2 procedure. The nominal SMYSwere used as the strength input.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0L r

K r

Figure A-4 Full-scale test data that fall within the defect size and CTOD limitations

plotted on the FAD of the Level 1 Option 2 procedure. The measured yieldstresses were used as the strength input.

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A.6 References

1 Wang, Y.-Y., Rudland, D., Horsley, D., Development of a FAD-Based Girth Weld ECAProcedure, Part I Theoretical Framework, Proceedings of the 4 th International Pipeline

Conference, Calgary, Alberta, Canada, September 29-October 3, 2002.2 Wang, Y.-Y., Rudland, D., Horsley, D., Development of a FAD-Based Girth Weld ECA

Procedure, Part II Experimental Verification, Proceedings of the 4 th International PipelineConference, Calgary, Alberta, Canada, September 29-October 3, 2002.

3 Pick, R. J., Glover, A. G., and Coote, R. I., Full Scale Testing of Large Diameter Pipelines,Proceedings of Conference on Pipeline and Energy Plant Piping, Pergamon Press, 1980, pp.357-366.

4 Glover, A. G., Coote, R. I., and Pick, R. J., Engineering Critical Assessment of Pipeline GirthWelds, Proceedings of Conference on Fitness for Purpose Validation of Welded Construction,The Welding Institute, Paper 30, 1981.

5 Erdogan, F., "Theoretical and Experimental Study of Fracture in Pipelines ContainingCircumferential Flaws," DOT-RSPA-DMA-50/83/3, Contract DOT-RC-82007 Final Report toUSDOT, September 1982.

6 Hopkins, P., Demofonti, G., Knauf, G., and Denys, R., an Experimental Appraisal of theSignificance of Defects in Pipeline Girth Welds, 8 th EPRG/PRC Biennial Joint TechnicalMeeting on Line Pipe Research, Paris, 1991.

7 Wilkowski, G. M., and Eiber, R. J., "Evaluation of Tensile Failure of Girth Weld RepairGrooves in Pipe Subject to Offshore Laying Stresses," Journal of Energy ResourcesTechnology, v. 103, March 1981.

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Appendix B Validation of the Assessment Procedures against Curved WidePlate Tests

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B.1 Background

This appendix provides further validation of the Level 1 Option 2 procedure, usingexperimental test data from curved wide plates. Since the plastic collapse criterionimplemented in the Level 1 Option 1 procedure is a part of the Option 2 procedure, this

validation is also an indirect confirmation of the Option 1 procedure.This validation is similar to the PRCI-funded work of Wang, et al. [ 1]. It is useful as this

is a direct confirmation of the proposed assessment procedures, which incorporate theimprovements to the prior work as listed in Section A.1.

This appendix also covers the validation of the assessment with the option ofincorporating the effects of weld strength mismatch. The inclusion of the weld strengthmismatch is further discussed in Appendix F.

B.2 Overview of the Wide Plate Tests

The test data were taken from 31 curved wide plate (CWP) tests performed at theUniversity of Gent [ 2]. The pipe material was a longitudinally welded API 5L X60 pipe with36-inch (914.4 mm) OD and 11.6-mm (0.457-inch) wall. The averaged 0.5% proof stress inthe longitudinal direction was 64.7 ksi (446 MPa). The averaged tensile strength in the samedirection was 81.2 ksi (560 MPa). There were ten girth welds made with seven combinationsof cellulosic electrodes (AWS Exx10). This offered seven levels of weld strength mismatchranging from 20% undermatching to 24% overmatching.

The CWPs were cut from welded pipe sections in the longitudinal direction with the girthweld in the mid-length. The girth weld defects were introduced by sharp starter notch andfatigue pre-cracked. The gauge section of the CWPs had a nominal width of 300 mm. All

CWPs were loaded in tension until failure. The load, overall deformation, and CMOD (crackmouth opening displacement) were recorded during the tests. The test temperatures were 10, -30, and 50 oC.

B.3 Validation Process

The validation process consists of three input options (IO). Each IO represents differentlevels of available data that might be encountered in practice.

The IO 1 assumes the following input data are available:1. Pipe diameter,2. Pipe wall thickness,3. Pipe grade,4. Defect depth,5. Defect length,6. CTOD toughness, and7. Applied longitudinal stress.

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In IO 2, the pipe grade is replaced with the measured pipe yield stress and tensilestrength.

In IO 3, the measured yield stress and tensile strength of the pipe material and weldmetals are both known. The effectiveness of incorporating the weld strength mismatch in theassessment procedures is evaluated in this IO.

B.4 Validation Results against Curved Wide Plate Test Data

The assessment results are given in FAD format in Figure B-1, Figure B-2 , and FigureB-3 and in tabulated form in Table B-1 . The assessment points are listed for all cases. Inaddition, the safety factors in terms of applied stress are also listed. The safety factor is theratio of the experimentally measured maximum stress over the predicted failure stress.

The results of IO 1 are given in Figure B-1. There is a single cut-off of the FAC for allcases, as the cut-off is related to the nominal pipe grade. The median value of the safetyfactor is 1.23 with a standard deviation of 0.11. All test cases are conservatively predicted,

even for the undermatched cases. This is the direct result of using the nominal pipe grade asthe strength input. The actual pipe strength was higher. The weld strength mismatch is notconsidered in this IO.

The results of IO 2 are given in Figure B-2. The single cut-off of the FAC for all cases isdetermined by the measured yield and tensile strength of the pipe. The median value of thesafety factor is 1.12 with a standard deviation of 0.10. Since the measured tensile propertiesare greater than the SMYS (pipe grade), the assessment procedure predicted higher failurestresses than those obtained if the nominal pipe grades are used. Consequently, some of theundermatched cases are not conservatively predicted. The weld strength mismatch is notconsidered in this IO.

The results of IO 3 are given in Figure B-3. The cut-off of the FAC is affected by theweld strength mismatch, therefore, represented by a broken line. The median value of thesafety factor is 1.12 with a standard deviation of 0.07. One case has a safety factor of 0.99.All others are conservatively predicted. In comparison to other IOs, this one is clearly the

best, as it offers the lowest standard deviation and very good overall accuracy. Thisdemonstrates that the accuracy of the procedure is improved with the inclusion of the weldstrength mismatch effects.

B.5 Observation from the Validation against Curved Wide Plate Test Data

It should be noted that no safety factor was applied when the assessment procedure is

validated against the curved wide plate test data. The assessment procedure is assumed to predict critical failure events. In the recommended acceptance criteria, a safety factor of 1.5is applied after the critical defect size is determined. The recommended acceptance criteriahave a higher degree of conservatism than that shown in this appendix.

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78 03-G78-20

1. In comparison with the validation against the full-scale test data, the assessment procedure showed a higher degree of consistency and accuracy. This is reflectedin the small values of standard deviation.

2. In the absence of explicit consideration for weld strength mismatch, theassessment procedure is conservative and accurate when the weld strength at leastovermatches that of the pipe.

3. When the weld strength mismatch levels were taken into account, the new procedure produced consistent and highly accurate predictions against theexperimental results.

4. If the pipe grade is the only known strength input, even or over-matching weldmetal is necessary to ensure conservative predictions.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.5 1.0 1.5 2.0L r

K r

Figure B-1 Curved wide plate test data plotted on the FAD of the Level 1 Option 2

procedure. The nominal SMYS were used as the pipe strength input.

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78 03-G78-20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.5 1.0 1.5 2.0L r

K r

Figure B-2 Curved wide plate test data plotted on the FAD of the Level 1 Option 2

procedure. The measured yield and tensile strength of the pipe were used asthe pipe strength input.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.5 1.0 1.5 2.0L r

K r

Figure B-3 Curved wide plate test data plotted on the FAD of the procedure that is an

extension of the Level 1 Option 2 procedure. The measured yield and tensilestrength of the pipe AND weld were used as the strength input.

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78 03-G78-20

Table B-1 Summary of the Validation against the Curved Wide Plate Test Data

L r

K r

F a c

t o r o

f S a f e t y

i n S t r e s s

L r

K r

F a c

t o r o

f S a f e t y

i n S t r e s s

L r

K r

F a c

t o r o

f S a f e t y

i n S t r e s s

(MPa) (MPa) (mm) (mm) (mm)1 359 461 0.80 0.82 0.26 3.50 48.7 1.19 0.32 1.08 1.11 0.30 0.98 1.29 0.30 1.156 415 527 0.93 0.94 0.24 3.70 45.6 1.25 0.35 1.14 1.16 0.33 1.03 1.23 0.33 1.09

11 473 598 1.06 1.07 0.14 3.90 45.0 1.20 0.45 1.09 1.11 0.43 1.01 1.09 0.43 0.9928 533 649 1.20 1.16 0.21 3.40 48.0 1.56 0.45 1.42 1.45 0.42 1.29 1.38 0.42 1.2224 554 646 1.24 1.15 0.27 3.60 48.5 1.53 0.40 1.38 1.42 0.38 1.26 1.33 0.38 1.182 359 461 0.80 0.82 0.37 3.50 27.1 1.12 0.23 1.01 1.04 0.21 0.92 1.21 0.21 1.073 359 461 0.80 0.82 0.37 4.30 48.0 1.25 0.31 1.13 1.16 0.29 1.03 1.38 0.29 1.22

7 415 527 0.93 0.94 0.30 3.80 25.7 1.27 0.30 1.16 1.18 0.28 1.05 1.25 0.28 1.118 415 527 0.93 0.94 0.30 4.30 49.3 1.29 0.35 1.17 1.19 0.33 1.06 1.27 0.33 1.1212 473 598 1.06 1.07 0.18 4.10 25.0 1.37 0.42 1.24 1.27 0.40 1.12 1.25 0.40 1.1013 473 598 1.06 1.07 0.18 3.70 50.5 1.25 0.41 1.14 1.16 0.39 1.03 1.14 0.39 1.0116 488 586 1.09 1.05 0.28 4.70 50.3 1.51 0.45 1.37 1.40 0.42 1.24 1.36 0.42 1.2017 488 586 1.09 1.05 0.28 4.20 72.4 1.33 0.39 1.20 1.23 0.37 1.09 1.20 0.37 1.0620 498 614 1.12 1.10 0.23 4.80 48.6 1.44 0.48 1.30 1.33 0.45 1.18 1.29 0.45 1.1421 498 614 1.12 1.10 0.23 3.40 73.6 1.45 0.42 1.32 1.35 0.39 1.19 1.31 0.39 1.1629 533 649 1.20 1.16 0.12 4.00 23.3 1.61 0.60 1.46 1.49 0.56 1.34 1.42 0.56 1.2930 533 649 1.20 1.16 0.12 4.30 49.7 1.29 0.56 1.20 1.20 0.53 1.12 1.14 0.53 1.0825 554 646 1.24 1.15 0.13 3.50 22.2 1.58 0.53 1.43 1.47 0.50 1.30 1.38 0.50 1.2326 554 646 1.24 1.15 0.13 4.10 49.8 1.36 0.56 1.25 1.26 0.52 1.16 1.18 0.52 1.104 359 461 0.80 0.82 0.26 3.60 24.0 1.22 0.30 1.11 1.14 0.28 1.01 1.33 0.28 1.185 359 461 0.80 0.82 0.26 3.00 48.5 1.28 0.31 1.16 1.19 0.29 1.05 1.37 0.29 1.229 415 527 0.93 0.94 0.24 4.20 26.8 1.30 0.36 1.18 1.20 0.33 1.07 1.27 0.33 1.13

10 415 527 0.93 0.94 0.24 2.50 47.2 1.30 0.30 1.18 1.21 0.28 1.07 1.26 0.28 1.1214 473 598 1.06 1.07 0.14 3.40 24.1 1.41 0.46 1.28 1.31 0.43 1.16 1.29 0.43 1.1415 473 598 1.06 1.07 0.14 3.50 48.5 1.34 0.48 1.21 1.24 0.45 1.11 1.22 0.45 1.0918 488 586 1.09 1.05 0.13 2.90 23.2 1.37 0.43 1.24 1.27 0.40 1.12 1.24 0.40 1.1019 488 586 1.09 1.05 0.13 3.50 49.6 1.36 0.51 1.23 1.26 0.48 1.14 1.23 0.48 1.1122 498 614 1.12 1.10 0.11 3.10 24.5 1.40 0.49 1.27 1.29 0.46 1.15 1.26 0.46 1.1223 498 614 1.12 1.10 0.11 3.80 50.2 1.36 0.58 1.26 1.26 0.54 1.17 1.22 0.54 1.1431 533 649 1.20 1.16 0.06 4.00 47.3 1.35 0.79 1.36 1.25 0.74 1.26 1.18 0.74 1.2227 554 646 1.24 1.15 0.07 5.00 49.0 1.23 0.76 1.26 1.14 0.71 1.17 1.07 0.71 1.12

Median 488 598 1.09 1.07 0.21 3.70 48.0 1.34 0.43 1.23 1.24 0.40 1.12 1.26 0.40 1.12Std. Dev. 65 65 0.14 0.12 0.08 0.56 13.9 0.12 0.13 0.11 0.11 0.12 0.10 0.09 0.12 0.07

M i s m a t c h R

a t i o a t

U T S

IO 3, UsingMeasured Yieldand Tensile of

Pipe and Welds

D e f e c

t H e i g

h t

D e f e c t

L e n g

t h

T e s t N o .

W e l

d T e n s i

l e

C T O D

IO 2, UsingMeasured Yieldand Tensile of

Pipe

W e l d

Y i e l d

IO 1, UsingSMYS of Pipe

M i s m a t c h

R a t

i o a t

Y i e l d

B-6


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B.6 References


2 Denys, R. M., The Effect of Weld Metal Matching on Girth Weld Performance, Volume II Experimental Investigation, final report to the Pipeline Research Committee of the AmericanGas Association, PR-202-922, January 24, 1993.

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Appendix C Stress Intensity Factor Solution

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C.1 Background

Chapuloit, et al., conducted over 200 3-D FE analyses of pipes containing finite-lengthsemi-elliptical defects [ 1]. The K I solutions were derived for pipes with D/t ratio rangingfrom 4 to 162 and a/t ratio up to 0.8. The solutions were also calibrated with the flat plate

solutions of Newman and Raju and Irwins analytical solution of an elliptical crack in aninfinite body [ 2,3]. Overall, Chapuloits solutions are perhaps one of the mostcomprehensive solutions in the published literature for circumferentially-cracked pipes under

bending loads.

In the previously published PRCI-funded work of Wang, et al. [ 4,5], the K I solutions ofChapuloit at the deepest point were fitted to a set of parametric equations. The K I solutionstook a similar form as those of ASME Section XI solutions. However, due to the use of ahigh order polynomial function in the parametric equations, the fitted equations did not givecorrect K I values at either very small or large a/t ratios. As shown by an example in FigureC-1, the trends at a/t < 0.1 and a /t > 0.6 are not consistent with the original data.

Furthermore, the overall fit has some oscillation even within the range of 0.1 < a/t < 0.6 dueto the high order polynomial functions.

A new fitting was conducted to remove the polynomial functions. The new parametric equations provide more consistent agreement with the original data as shown inFigure C-1.

0.8

1.0

1.2

1.4

1.6

1.8

0.0 0.2 0.4 0.6 0.8 1.0a/t

F b

Previous FitCurrent Fit

Data of Chapuloit

D /t =82, =0.012

Figure C-1 Comparison of the fitted equations as a function of defect depth ratio

C-2


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78 03-G78-20

C.2 Parametric Equations

The newly fitted equations are given as follows.

t a

Dc

t D ===

,

2, (C.1)

ba I F a K = (C.2)

( ) 2806.01983.0906.0791.031.209.1,, mm

F b

+++= (C.3a)

21 345.0163.000985.0 =m

22 155.018.200416.0 +=m

Additional corrections apply to F b for the following defect conditions,

( )

==

,80

,,, bb F F

if 1.0 and ,

80

>

( )

(C.3b)

,

.

1080>

8.01.

==

,

1.080,,, bb F F 1.0if


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78 03-G78-20

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.03 0.06 0.09 0.12 0.15

F b

= 0.1 = 0.2 = 0.4 = 0.6

= D/t = 42

Figure C-2 Comparison of the fitted curves with the original data of Chapuloit for pipes

with D /t of 42. The symbols are from the original data and the curves arefrom the fitted equations.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.00 0.03 0.06 0.09 0.12 0.15

F b

= 0.1 = 0.2 = 0.4 = 0.6

= D/t = 82



C-4


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78 03-G78-20

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.00 0.03 0.06 0.09 0.12 0.15

F b

= 0.1 = 0.2 = 0.4 = 0.6

= D/t = 162



C.4 References

1 Chapuloit, S., Lacire, M. H., and Le Delliou, P., Stress Intensity Factors for Internal

Circumferential Cracks in Tubes over a Wide Range of Radius over Thickness Ratios, PVPVol. 365, ASME 1998, pp. 95-106.

2 Newman, J. C., Jr. and Raju, I. S., Analysis of Surface Cracks in Finite Plates Under Tensionand Bending Loads, NASA Technical Paper 1578 , NASA, Washington, D. C., December1978.

3 Irwin, G. R., Crack-extension force for a part-through crack in a plate, Journal of Applied Mechanics , Vol. 29, 1962, pp. 651-654.



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Appendix D Plastic Collapse Solution

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D.1 Background

Plastic collapse solutions suitable for girth weld defect assessments have beeninvestigated extensively by Wang [ 1,2 ]. There are several earlier reviews, e.g., Rosenfeld [ 3] and Clyne and Jones [ 4], that targeted pipelines. Miller [ 5] conducted an extensive review of

limit load solutions for a wide range of structural geometries, including pipes.The plastic collapse solution adopted here follows the recommendation of Wang [ 6,7 ].

The basis of the recommendation has been covered extensively in prior publications. The plastic collapse solution is due to Miller [ 5],

( )

=

2sin

2cos

f

Miller c (D.1)

where is the nominal longitudinal stress at plastic collapse. The Miller solution of Eq.

(D.1) was compared with the full-scale test data of Glover [

Miller c

8,9 ] and Erdogan [ 10]. The

features of the test database are described in Appendix A. Based on the comparison, a defectsize correction factor was proposed [ 6],

( )

=

2sin

2cos

f

Girthc f (D.2)

where is the nominal longitudinal stress at plastic collapse of a girth weld with the

correction factor f . The defect size correction factor f was given as [ 6],

Girthc

05.0

14

1

1

+= f if 0.05 (D.3a)

4 = f if > 0.05 (D.3b)

The modified Miller solution of Eqs. (2) and (3) is the basis of the revised plasticcollapse criterion in CSA Z662 Appendix K 2003 Edition. The acceptance criteria of CSAZ662 Appendix K has a safety factor of 2 on the defect length computed from Eqs. (2) and(3). This safety factor is consistent with historical recommendations.

D.2 New Defect Size Correction Factor

The plastic collapse solution of Eqs. (D.2) and (D.3) worked well in comparison to testdata [ 1,2,6,7 ]. However, the discontinuity of the first order derivative at = 0.05 can pose a

problem if the current assessment procedures are cast into an optimization procedure.Although this is not an immediate concern for this project, revisions were made to the defectsize correction factor.

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( ) 5.205.03854

+= f if 0.05 (D.4a)

4 = f if > 0.05 (D.4b)

D.3 Comparison with Full-scale Test Data

The bending stresses at the critical events in the full-scale tests, normalized by the plasticcollapse stresses of Eq. (D.1) are shown in Figure D-1. When the stress ratio is greater than1.0 on the y-axis, the actual failure stress is greater than the predicted plastic collapse stress.In such cases, the Miller solution is conservative. It is evident from Figure D-1 that theMiller solution is less conservative for larger defects. A defect size correction line, Eq.(D.3), was suggested by Wang [ 6]. The new defect size correction line, corresponding to Eq.(D.4), is also shown in the figure. The new correction line gives lower plastic collapse stress,and therefore, is more conservative than the prior correction line.

It should be noted that no minimum toughness criterion is applied to the test data.Consequently, it was not expected that all test data would fall conservatively above thecorrection line. The test data are used to set the overall trend.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

c E x p

/

c M i l l e r

Full-Scale Test Data

Prior Defect Size Correction Line

New Defect Size Correction Line

Figure D-1 Comparison of the Miller plastic collapse solution and the full-scale test data.

The prior and current defect size correction lines are shown.

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D.4 References

1 Wang, Y.-Y., Wilkowski, G. M., and Horsley, D. J., Plastic Collapse Analysis of PipelinesContaining Surface-Breaking Circumferential Defects, in Pipeline Technology, Vol. I, R.

Denys, Ed., Elsevier Science B. V., May 21-24, 2000, pp. 191-209.2 Wang, Y.-Y., Wilkowski, G. M., and Horsley, D. J., Plastic Collapse Analysis of Pipeline

Girth Welds, in Assessment Methodologies for Preventing Failure: Deterministic and Probabilistic Aspects and Welding Residual Stress, Vol. 1 ASME PVP-Vol. 410-1 , Edited by R.Mohan, 2000, pp. 3-9.

3 Rosenfeld, M. J., "Serviceability of Corroded Girth Welds," Draft Final Report, PRI Contract No. PR 218-9438, March 31, 1995.

4 Kastner, W., Roehrich, E., Schmitt, W., and Steinbuch, R., Critical Crack Sizes in DuctilePiping, International Journal of Pressure Vessel and Piping, Vol. 9, 1981, pp.197-219.

5 Miller, A. G., "Review of Limit Codes of Structure Containing Defects," International Journalof Pressure Vessels and Piping, Vol. 32, 1988, pp. 191-327.



8 Pick, R. J., Glover, A. G., and Coote, R. I., Full Scale Testing of Large Diameter Pipelines,Proceedings of Conference on Pipeline and Energy Plant Piping, Pergamon Press, 1980, pp.357-366.

9 Glover, A. G., Coote, R. I., and Pick, R. J., Engineering Critical Assessment of Pipeline GirthWelds, Proceedings of Conference on Fitness for Purpose Validation of Welded Construction,The Welding Institute, Paper 30, 1981.

10 Erdogan, F., "Theoretical and Experimental Study of Fracture in Pipelines ContainingCircumferential Flaws," DOT-RSPA-DMA-50/83/3, Contract DOT-RC-82007 Final Report toUSDOT, September 1982.

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Appendix E Estimation of Applied Stress from Applied Strain

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E.1 Assumed Stress Strain Relations

Sometimes, it is easier to determine the applied longitudinal strain than the appliedlongitudinal stress. When applied stress is needed for computation, such as for thedetermination of applied stress in the application of the Level 1 Option 1 procedure, the

following process may be followed.The overall stress strain curve is assumed to take the form that is suggested in CSA Z662,

n

y

a yaa E E

+=

005.0 , (E.1)

where is the nominal yield stress (SMYS) and E is the Youngs modulus. There is an

unique relation between applied stress y

a and applied strain a , if the strain hardening

exponent n is known.

E.2 Estimation of Strain Hardening Exponent

By assuming a pure power stress strain relation, the strain hardening exponent may beestimated as,

( )( ){ }T Y

n t //1ln005.0/ln = . (E.2)

E.3 Estimation of Y / T Ratio from Pipe Grade or Yield Stress

Webster and Bannister examined the correlation of Y /T ratio and yield strength [ 1]. Twosimple relations were produced, one providing upper bound Y /T ratio, the other providing the

best fit to the data. The relations were derived from theoretical and empirical considerations,and are applicable to many kinds of structural steels. Mannucci, et al., found the relations to

be reasonable for pipeline steels tested in longitudinal direction [ 2]. The comparison of thelinepipe test data and the upper bound and best fit relations is shown in Figure E-1.

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Figure E-1 Comparison of linepipe longitudinal test data with the Webster and Bannistercorrelation equations [ 2]

0.7

0.8

0.9

1.0

50 60 70 80 90 100 110 120Grade (ksi)

Y / T

Upper Bound, Webster and Banister CSA Appendix KEq. 1 of the Current Document

API min Y and T requirementsBest Fit, Webster and Banister

Figure E-2 Comparison of the relations between Y /T ratio and pipe grades from

estimation equations and codes

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The relations for the upper bound and best fit by Webster and Bannister are shown inFigure E-2. Some reference points are added by computing the Y /T ratio from the API 5Lminimum yield and tensile requirements. In addition, the plastic collapse criterion of CSAZ662 Appendix K 2003 provides a reference table between pipe grade and flow stress. Theimplied Y /T ratio may be obtained when the flow stress is taken as the averaged value

between yield and tensile strength. The API 5L and CSA Z662 values are also shown inFigure E-2. A new equation in the same format as that of Webster and Banister, but

providing the best fit to the API 5L and CSA Z662 Appendix K, is suggested as follows,

25.2

75.2121

1/

+

=

y

T Y

. (E.3)

The nominal yield stress is in the unit of ksi. y

E.4 Estimation of Uniform StrainEstimating the strain at the ultimate tensile strength (UTS), often termed uniform strain

or tensile strain , can be difficult. It is generally true that the uniform strain is inverselyrelated to pipe grade. The following equation is suggested for grades up to X100 if no other

proven estimation procedure is available.

22.000175.0 += yt

y

. (E.3)

The nominal yield stress is in the unit of ksi.

E.5 References

1 Webster, S., Bannister, A., Engineering Fracture Mechanics , Vol. 67 (2000), pp. 481-514.

2 Mannucci, G., Di Vito, L., Malatesta, G., Izquierdo, A., and Cumino, G., Evaluation of theEffect of Yield-to-Tensile Ration on the Structural Integrity of an Offshore Pipeline by a Limit-State Design Approach, Proceedings of the 4 th International Conference on PipelineTechnology, May 9-13, 2004, Ostend, Belgium, pp. 1283.

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Appendix F Incorporation of Weld Strength Mismatch

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F.1 Background

The effects of weld strength mismatch on the weld integrity have received great attentionin the last two decades. There were two international symposia organized by GKSS(Germany) dedicated to this subject [ 1,2 ]. With the trend towards using high-strength

linepipes, girth weld strength undermatching has become a distinct possibility [ 3]. It istherefore necessary to consider how girth welds with mismatching welds should be assessed.

Early work by Wang indicated that the effects of weld strength mismatch in ECA procedures of FAD format can be accounted for by scaling the stress ratio ( S r or Lr ) [4,5,6 ].The newly developed European structural integrity assessment procedure SINTAP hasadopted this approach [ 7]. Therefore, the weld strength mismatch effects can be effectivelyincorporated into the ECA procedure by providing a correction factor to the plastic collapsesolutions,

Girthc Mis

Misc f = (F.1)

where is the mismatch corrected plastic collapse stress and is the mismatchcorrection factor.

Misc Mis f

Extensive studies have been conducted by researchers at GKSS on the effects of weldstrength mismatch on the plastic collapse loads. The results of these studies have beenincorporated into a structural integrity assessment procedure termed Engineering TreatmentModel, or ETM [ 8,9 ]. They did not, however, study pipes with finite length girth welddefects. The geometry that most closely matches the girth welds in pipes is pipes containingfully-circumferential surface-breaking defects. The mismatch correction factor from this

geometry was found to provide good approximation by Wang [ Mis f

10]. The formulae for the

mismatch correction factor are given in the same reference.F.2 Determination of Weld Width for Girth Weld

One of the key parameters in the mismatch correction factor is the weld width. Theoriginal GKSS work assumed the welds are parallel-sided. For a typical girth weld, the weldwidth (2 H ) corresponding to the defect depth may be used as the weld width in determiningthe mismatch correction factor, see Figure F-1.

2

Figure F-1 Determination of weld width 2H for a typical girth weld geometry

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F.3 Suggested Approach for the Treatment of Weld Strength Mismatch

A multi-level approach may be taken in the treatment of weld strength mismatch,depending on the availability of weld property data.

Level 1: If the weld tensile property is not known, conservative assessment can be

conducted by (1) using the pipe tensile property and (2) ensuring the weldmetal strength even- or over-matches the pipe tensile property. This is thedefault condition assumed in the Level 1 assessment procedure.

Level 2: If the weld tensile property is known, but the weld profile is not known,conservative assumption can be made on the weld width and the assessmentcan be done by incorporating the weld strength mismatching effects. Forundermatching welds, upper bound weld width should be assumed. Forovermatching welds, lower bound weld width should be assumed.

Level 3: If the weld tensile property and the weld profile are known, the assessmentcan be done using the actual properties and dimensions.

Care should be taken when assessing defects on the fusion boundary. The lower of the base and weld metal tensile property should be taken when a single value of tensile propertyis needed, such as converting stress intensity factor K I to CTOD. The crack tip deformationis dominated by the lower strength material for fusion boundary defects [ 11 ]. For weldcenterline defects, the tensile properties of the weld metal should be taken.

F.4 References

1 Schawalbe, K.-H., etc., Mis-Matching of Welds, First International Symposium on Weld Metal

Mis-Matching , Luneburg, Germany, April 1993.2 Schawalbe, K.-H., etc., Mis-Matching of Welds, Second International Symposium on Weld

Metal Mis-Matching , Luneburg, Germany, April 24-26, 1996.

3 D. J. Horsley and A. G. Glover, Girth Weld Strength Under-Matching in High Pressure Natural Gas Pipelines, Second International Symposium on Weld Metal Mismatching ,Schawalbe, etc., Eds., Luneburg, Germany, April 24-26, 1996.

4 Wang, Y.-Y., Kirk, M. T., Gordon, J. R., and Pisarski, H. G., Incorporating Weld MetalMismatch into Structural Integrity Assessment, in Pipeline Technology , Vol. 1, R. Denys,Eds., Elsevier Science B. V., 1995, pp. 475-486.

5 Wang, Y.-Y., and Kirk, M. T., The Effect of Weld Metal Strength Mismatch and Structural

Geometry on Failure Assessment Diagram, Second International Symposium on Weld Metal Mis-Matching , Schawalbe, etc., Eds., Luneburg, Germany, April 24-26, 1996.

6 Wang, Y.-Y., and Kirk, M. T., A Structural Assessment Procedure for Welded Structures withWeld Metal Strength Mismatch, ASME PVP Conference , Montreal, July 22-26, 1996.

7 SINTAP Procedure, Final Version, November 1999.

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8 Schawable, K.-H., etc., EFAM ETM 97 The ETM Method for Assessing the Significance ofCrack-Like Defects in Engineering Structures, Comprising the Versions ETM 97/1 and ETM96/2, GKSS 98/E/6, Geesthacht, 1998.

weld code revision progress report

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