HSE Health & Safety

Executive

Growth of through-wall fatigue cracks in brace members

Prepared by TWI Ltd for the Health and Safety Executive 2004

RESEARCH REPORT 224

HSE Health & Safety

Executive

Growth of through-wall fatigue cracks in brace members

Dr Marcos Pereira TWI Ltd

Granta Park Great Abington

Cambridge CB1 6AL

The total fatigue life of a brace in an offshore jacket structure is conventionally considered in four parts. N1 is the number of cycles to initiate the first discernible surface cracking as noted by any available method. N2 is the number of cycles to detect surface cracking by visual examination without the use of crack enhancement or optical aids. N3 is the number of cycles until the first through wall cracking and N4 is the total number of cycles to the end of test or final separation of the member. The majority of fatigue tests conducted on tubular connections or on girth welds in brace members obtained only N3 results, it being common practice to stop testing when a through wall crack was present. In the HSE Guidance the S-N curves for tubular connections and girth welds in braces are therefore based on N3 data. (In fact it should be noted here that there were very few test results for single sided girth welds available at the time of drafting the HSE guidance; the choice of Class F2 for these joints was therefore based largely on judgement rather than data).

In UK waters, flooded member detection (FMD) by ultrasonic inspection with a remotely operated vehicle is used to check whether through cracks are present; however, in practice, fatigue cracks are likely to continue to grow around the brace circumference after breaking through-wall. A review by Sharp (Ref.1) concluded that detailed knowledge of the crack shape development after breakthrough together with a value for the ratio N4/N3 are required. From the structural safety viewpoint, there is clearly a need to quantify the rate of fatigue crack growth after development of a through wall crack, but prior to the point at which final separation becomes a possibility. The present study was designed to examine these factors for circumferential welds in tubular members, and hence allow the efficacy of the FMD strategy to be assessed.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

HSE BOOKS

© Crown copyright 2004

First published 2004

ISBN 0 7176 2867 1

All rights reserved. No part of this publication may bereproduced, stored in a retrieval system, or transmitted inany form or by any means (electronic, mechanical,photocopying, recording or otherwise) without the priorwritten permission of the copyright owner.

Applications for reproduction should be made in writing to:Licensing Division, Her Majesty's Stationery Office, St Clements House, 2-16 Colegate, Norwich NR3 1BQ or by e-mail to hmsolicensing@cabinet-office.x.gsi.gov.uk

ii

CONTENTS

EXECUTIVE SUMMARY vBackground vObjectives vWork Carried Out vConclusions vRecommendations vi

1. INTRODUCTION 1

2. OBJECTIVES 3

3. PROJECT OVERVIEW 5

4. SCOPE OF WORK 7

4.1. TASK 1 – SPECIMEN MANUFACTURE 7

4.2. TASK 2 – TESTING FIXTURE DESIGN AND COMMISSIONING 7

4.3. TASK 3 – FATIGUE TESTING 8

4.4. TASK 4 – ANALYTICAL EVALUATION AND VALIDATION OF ANALYTICAL MODEL 9

5. RESULTS AND DISCUSSION 11

6. CONCLUSIONS 15

7. RECOMMENDATIONS 17

8. REFERENCES 19

FIGURES 1 – 2

TABLES 1 – 4

Appendix A – Material Certificates Appendix B – Welding Procedure Appendix C – Weld Inspection Certificates Appendix D – Fatigue Test Certificates Appendix E – Engineering Critical Analysis

iii

iv

EXECUTIVE SUMMARY BACKGROUND The total fatigue life of a brace in an offshore jacket structure is conventionally considered in four parts. N1 is the number of cycles to initiate the first discernible surface cracking as noted by any available method. N2 is the number of cycles to detect surface cracking by visual examination without the use of crack enhancement or optical aids. N3 is the number of cycles until the first through wall cracking and N4 is the total number of cycles to the end of test or final separation of the member. The majority of fatigue tests conducted on tubular connections or on girth welds in brace members obtained only N3 results, it being common practice to stop testing when a through wall crack was present. In the HSE Guidance the S-N curves for tubular connections and girth welds in braces are therefore based on N3 data.

In UK waters, flooded member detection (FMD) by ultrasonic inspection with a remotely operated vehicle is used to check whether through cracks are present; however, in practice, fatigue cracks are likely to continue to grow around the brace circumference after breaking through-wall. From the structural safety viewpoint, there is clearly a need to quantify the rate of fatigue crack growth after development of a through wall crack, but prior to the point at which final separation becomes a possibility. In this way the remaining safe life of the structure after through-wall cracking can be assessed, and hence the efficacy of the FMD strategy examined.

OBJECTIVES To carry out fatigue tests on tubular girth welds in order to determine their remaining fatigue life (N3-N4) after development of through wall cracks.

WORK CARRIED OUT A series of circumferential butt welds in steel pipe of 324mm outside diameter and 12.7mm wall thickness was fatigue tested under four point bending. The project was divided in four major tasks as described below:

Task 1 – Specimen manufacture Task 2 – Testing fixture design, commissioning and pre-test Task 3 – Fatigue testing Task 4 – Analytical evaluation and validation of analytical model

All tasks have now been completed; this report is the final one in the series.

CONCLUSIONS A series of fatigue tests on circumferential butt welds in steel pipe of 324mm outside diameter and 12.7mm wall thickness was conducted in which crack development prior to final failure was examined in detail. The results lead to the following conclusions.

x A value of 1.1 can be reasonably assumed for the ratio N4/N3 for the girth welds investigated here.

x It is evident that the remaining fatigue life could be only slightly greater than the endurance. This has important implications on the use of flooded member detection (FMD) and the selection of an appropriate inspection interval needs to be taken into careful consideration in the development of a structural integrity management strategy.

v

x Conservative estimations of fatigue endurance of tubular girth welds can be achieved using the current formulations of BS 7910 and the fatigue crack growth mean line for R~0.1 (Ref.3).

RECOMMENDATIONS x It is recommended that further investigation be undertaken to incorporate in the fatigue

crack growth formulation of BS 7910, methods to estimate the growth of the first observed through crack (based on N3) until a fully developed through crack (based on N*) is achieved. For this purpose, further fatigue tests will be required in order to measure the fatigue crack length and height during testing. Finite element analysis may also provide K solutions in order to estimate the crack growth ratios that should be applied in the N3 to N* interval.

x It is also recommended that further tests be carried out in order to study the fatigue crack shape development, which is essential to validate fatigue crack growth formulations developed within the N3 to N* interval.

x Behaviour is likely to be influenced by the wall thickness to diameter ratio. Further tests for tubes of different dimensions are therefore recommended in order to allow broader application of these findings.

x The results provide a limited statistical dataset and need to be considered further in conjunction with the wider data in the literature.

Note: N* is the total number of cycles from the start of testing required for a surface crack to develop and grow to a nominally straight fronted through wall crack, i.e. when the external and internal crack lengths are roughly equal.

vi

1. INTRODUCTIONThe total fatigue life of a brace in an offshore jacket structure is conventionally considered in four parts. N1 is the number of cycles to initiate the first discernible surface cracking as noted by any available method. N2 is the number of cycles to detect surface cracking by visual examination without the use of crack enhancement or optical aids. N3 is the number of cycles until the first through wall cracking and N4 is the total number of cycles to the end of test or final separation of the member. The majority of fatigue tests conducted on tubular connections or on girth welds in brace members obtained only N3 results, it being common practice to stop testing when a through wall crack was present. In the HSE Guidance the S-N curves for tubular connections and girth welds in braces are therefore based on N3 data. (In fact it should be noted here that there were very few test results for single sided girth welds available at the time of drafting the HSE guidance; the choice of Class F2 for these joints was therefore based largely on judgement rather than data).

In UK waters, flooded member detection (FMD) by ultrasonic inspection with a remotely operated vehicle is used to check whether through cracks are present; however, in practice, fatigue cracks are likely to continue to grow around the brace circumference after breaking through-wall. A review by Sharp (Ref.1) concluded that detailed knowledge of the crack shape development after breakthrough together with a value for the ratio N4/N3 are required. From the structural safety viewpoint, there is clearly a need to quantify the rate of fatigue crack growth after development of a through wall crack, but prior to the point at which final separation becomes a possibility. The present study was designed to examine these factors for circumferential welds in tubular members, and hence allow the efficacy of the FMD strategy to be assessed.

1

2

2. OBJECTIVESTo carry out fatigue tests on tubular girth welds in order to determine their remaining fatigue life (N3-N4) after development of through wall cracks.

3

4

3. PROJECT OVERVIEW The project was divided in four major tasks as described below:

Task 1 – Specimen manufacture Task 2 – Testing fixture design, commissioning and pre-test Task 3 – Fatigue testing Task 4 – Analytical evaluation and validation of analytical model

All tasks have now been completed; this report is the final one in the series.

5

6

4. SCOPE OF WORK 4.1. TASK 1 – SPECIMEN MANUFACTURE In order to be as consistent as possible with earlier studies on tubular connections, particularly those conducted under the United Kingdom Offshore Steels Research Project (UKOSRP, Ref.2) the pipe grade selected was a BSI 7191 GR 355EN (EN 10210-1) with specified yield strength of 350MPa and fracture toughness measured in terms of Charpy energy of 27J at –20oC. The main pipe dimensions were 12in (324mm) outside diameter (OD) and 12.7mm wall thickness. The pipe material specification is given in Appendix A.

TWI developed a welding procedure for the girth welds using a single sided SMAW procedure similar to that used for North Sea offshore structures. The welding procedure details are given in Appendix B.

Eight specimens were prepared from 16 sections with the final specimen dimensions as shown in Fig.1. The sections were marked prior to flame cutting and welding in order to allow for consistent preparation of samples.

1400

Weld

Applied loads

350

Figure 1 Schematic illustration of fatigue testing arrangement (not to scale, dimensions in mm)

All specimens were inspected visually and by magnetic particle inspection (MPI) and X-ray non-destructive methods. The standard inspection criterion applied for the girth welds was BS EN 288-3 with reference level B of BS EN 25817. All welds passed the criteria adopted. The inspection certificates are given in Appendix C.

Following an accidental overload of one of the original specimens (W01-01) an additional specimen (W09-01) was prepared using the same welding procedure and inspection methods described above.

4.2. TASK 2 – TESTING FIXTURE DESIGN AND COMMISSIONING The fatigue tests were conducted under bending load. Four point loading was selected since this gives a relatively uniform stress field in the test section between the points of load application. A specially designed four point bending rig was manufactured as shown in Fig.2. The rig was commissioned and tested with specimen W07-01 (the first specimen to be tested in Task 3). Originally it was planned to pressurise a rubber sleeve around the girth weld with low pressure air, and to monitor the pressure as a means of detecting through-thickness cracking. Specimen W07-01 was tested in this way; however, the method proved to be unsatisfactory. It was decided

7

that further tests would be monitored internally using a digital camera to view the internal weld root bead at the position of maximum tensile stress, and by visual inspection of the exterior. This method proved to be successful and was used for all the remaining specimens.

Figure 2 Fatigue testing arrangement

4.3. TASK 3 – FATIGUE TESTING Fatigue testing was conducted under ambient laboratory conditions using a servo-hydraulic testing system of 1000kN capacity operating in load control. The testing frequency was in the range 1.0 to 1.5 Hz. Four electrical resistance strain gauges of 6mm gauge length (type FLA-6-11) were bonded to the pipe outer surface to measure the axial strain range, and hence allow the outer fibre axial stress range local to the joint to be estimated. Gauges 1 to 3 were placed at 6 o’clock position. The centre of the gauges 1 and 2 being 5mm from the weld toe, one gauge either side of the weld respectively. Gauge 3 was placed 85mm from the weld toe on the gauge 2 side. Gauge 4 was placed 5mm from the weld toe at 12 o’clock position. Applied stress ranges were selected to achieve lives in the range A to B cycles approximately. All tests were conducted with a tensile mean stress in the outer fibre at the location of failure, i.e. with a positive load ratio, R. The nominal stress ranges and mean stress values applied are shown in Table 1.

The tests were carried out in two stages. In the first stage, loading was applied until a through wall crack developed in the girth weld. Once the first crack was detected the number of cycles (N2) was recorded and the fatigue crack growth was monitored and measured constantly until a through wall crack was detected. The through wall cracks were detected by visually inspecting the external pipe wall at convenient intervals (number of cycles) that varied accordingly with the applied load. The size of the internal and external cracks were measured and monitored systematically in order to record the number of cycles for the first through wall crack (N3) and to determine the ratio of N2/N3 cycles. In the second stage, additional monitoring of the external

8

crack size was carried out in order to determine the number of cycles (N*)1 at which the crack had developed to a nominally straight fronted through wall crack, i.e. when the external and internal crack lengths were roughly equal. This stage was deemed to have been reached once the external crack length had grown to 90% of the internal length, at which stage monitoring was discontinued and the test was allowed to continue until unstable tearing occurred.

4.4. TASK 4 – ANALYTICAL EVALUATION AND VALIDATION OF ANALYTICAL MODEL In order to estimate the total number of cycles to failure for comparison with the experimental data generated in Task 3, assessments were made using a fracture mechanics approach based on BS 7910: amendment No.1 (Ref.3). A stress intensity factor solution derived for joints in flat plate (Clause M.3.2, M.5.1.3 and P.4.3.2 of BS 7910) was used. Stress intensity magnification factor (Mk) of flaws at weld toe was assumed according to Clause M.5.1.3 of BS 7910 (Mk 3D solutions). The assessments were undertaken in two stages. Stage 1 estimated the total number of cycles to grow an initial surface crack using the experimentally measured first crack size at N2 cycles obtained in Task 3 to the first through wall crack. Stage 2 estimated the total number of cycles to failure (i.e. when the final flaw length reached the limit of validation of BS 7910 flat plate formulation) using the re-characterized through wall crack size from the estimated first through wall crack size from stage 1. The initial crack sizes used in the assessments are summarized in Tables 3 and 4.

To carry out the fatigue crack growth assessments the software CRACKWISE 3, version 3.13, was used. Initially the BS 7910 recommended Paris Law constants for a stress ratio R>0.5 were used, however the results obtained were very conservative in terms of the estimated total number of cycles to failure. Paris law constants for the fatigue crack growth assumed in the assessments were then based on the mean line for a stress ratio R~0.1 (Ref. 4). Two sets of assessments were undertaken, i.e. two-stage fatigue crack growth and simplified fatigue crack growth curves as described in Ref.3 and 4. The fatigue thresholds assumed in the assessments are those from BS 7910: Amendment No.1.

1 Note: N* is the total number of cycles from the start of testing required for a surface crack to develop and grow to a nominally straight fronted through wall crack, i.e. when the external and internal crack lengths are roughly equal.

9

10

5. RESULTS AND DISCUSSIONNine specimens were fatigue tested and a summary of the results is shown in Table 1 and Fig.3. The fatigue test certificates are given in Appendix D.

10

Stre

ss ra

nge,

MPa

Class B ClassC Class D Class E N2 N3 N4

100

1000

1.E+05 1.E+06 1.E+07

Endurance N, cycles

Figure 3 Fatigue test results including N2, N3 and N4 measured cycles

As indicated above, Specimen W07-01, the first specimen tested, used air pressure to detect the through wall crack. The system did not work as planned and the specimen fractured while it was loaded overnight without through-thickness cracking being detected. From post mortem examination it was found that the internal crack shape did not allow the air to pass through the opened crack at a sufficient rate. Hence it was decided that in further tests visual inspection aided by a video camera would be used to detect the internal and external cracks, as described earlier. Therefore, the W07-01 initial crack size at N2 cycles and first through wall crack size at N3 cycles reported in Table 1 were estimated based on the strain gauge measurement and the last number of cycles monitored before a large crack was detected respectively. While these estimates were made in an attempt to retrieve some value from the test, clearly they are not valid test results and should be treated with caution.

From Table 1 it should be noted that tests W01-01 and W03-01, both tested at 100MPa stress range, were not continued to failure. W01-01 specimen achieved five million cycles without any visible internal or external cracks, at which point the test was terminated. W03-01 survived 2.8 million cycles without cracking, at which point a test machine malfunction gave rise to an overload, damaging the specimen beyond any possible repair. Due to these two different circumstances there are no N3 or N4 data available for the tests at 100MPa stress range.

11

All remaining specimens were tested successfully to failure, i.e. until unstable tearing occurred. For those specimens the initial internal crack sizes at N2 cycles and external crack sizes at N3 cycles, and the parameter N* as defined above, were successfully measured. These values are summarized in Table 1. Figure 4 shows the plots for all specimens that developed through wall cracks (N3) and the measured fatigue endurance N4 (in this figure the N2 data plots are omitted). Note that specimens W01-01 and W03-01 are plotted as run-out values together with the N4 values from other specimens.

10

Stre

ss ra

nge,

MPa

Class B ClassC Class D Class E N3 N4

100

1000

1.E+05 1.E+06 1.E+07

Endurance N, cycles

Figure 4 Fatigue test results showing N3 and N4 measured cycles. Also plotted are the run out values of

specimens W01-01 and W03-01 (N2) as N4 indicated with an arrow

Examination of the results in Table 1 suggests that an N4/N3 ratio of between 1.0 and 1.2 could be applied to the girth welds tested here.

The results of the fatigue crack growth assessments undertaken using the two stage and simplified fatigue crack growth curves are summarized in Tables 3 and 4. Figure 5 shows plots of the estimated and measured fatigue endurance ratio (N4est/N4) against the nominal stress range applied during the fatigue testing for the simplified and two stage fatigue crack growth assessments. The detailed assessment printouts are given in Appendix E.

The fatigue assessments were undertaken on specimens for which values of N2 were successfully measured. Tables 3 and 4 show that the best estimation of the measured N4 cycles is achieved using the simplified fatigue crack growth curve. The results also show that, for the majority of the cases studied, the formulation in BS 7910 yielded conservative estimates of actual fatigue life.

12

N4e

st/N

4 1.20

1.00

0.80

0.60

0.40

Simplified Two stage 0.20limit of failure

0.00

100 120 140 160 180 200 220 240 260

Stress range, MPa

Figure 5 Stress range plotted against the estimated/measured fatigue endurance ratio (N4est/N4)

Specimen W02-01 gave low fatigue endurances by comparison with the other specimens, as can be seen in Table 1 and Figure 3. In addition, the fracture mechanics assessment overpredicted the endurances for this test, see Tables 3 and 4. Results of the NDT conducted after specimen manufacture did not provide any explanation of this low result; similarly examination of the fatigue fracture surfaces (shown in Fig.6) found no fabrication flaw which would account for early fatigue development. It would therefore appear that this is a valid test result towards the lower side of the expected scatter, most likely as a result of local variability of the root bead profile.

D002506_01 Figure 6

Fracture surface of W02-01. Stress range 250MPa; Mean Stress 125MPa

13

A plot of the estimated and measured number of cycles at the first through wall crack and end of test (N4est/N3est and N4/N3) is shown in Fig.7. The plotted data lie below the diagonal showing

N4e

st/N

3est

that the assessments underestimated this ratio. The figure also shows that N4est/N3est converges to a value of 1.04 whilst the experimental data (Table 1) indicates a N4/N3 converging to a value of 1.1. The difference between the measured and assessed values can be attributed to the conservative estimation of fatigue crack growth according to BS 7910, since it did not take into account the endurance for the crack growth from the first observation of a through wall crack to a fully developed straight fronted through wall crack. Evidence of this is given in Tables 1, 3 and 4.

The ratio of the cycles to the first observed through crack/fully developed through crack (N*/N3) varied from 1.02 to 1.15. Using the estimated N3est and the measured N* the estimated ratio (N*/N3est) varies from 1.14 to 1.65 for the simplified fatigue crack growth curve (W02-01 excluded). This reflects the general conservatism in the predicted N3 values, N3est, compared to those observed in the test. A monitoring strategy could therefore be based on the predicted N3est values.

1.20

1.15

1.10

1.05

1.00 1.00 1.05 1.10 1.15 1.20

N4/N3

Figure 7 Plot of estimated (N3est/N4est) and measured (N3/N4) first through crack/fatigue endurance ratios

14

6. CONCLUSIONSA series of fatigue tests on circumferential butt welds in steel pipe of 324mm outside diameter and 12.7mm wall thickness was conducted in which crack development prior to final failure was examined in detail. The results lead to the following conclusions.

x A value of 1.1 can be reasonably assumed for the ratio N4/N3 for the girth welds investigated here.

x It is evident that the remaining fatigue life could be only slightly greater than the endurance. This has important implications on the use of flooded member detection (FMD) and the selection of an appropriate inspection interval needs to be taken into careful consideration in the development of a structural integrity management strategy.

x Conservative estimations of fatigue endurance of tubular girth welds can be achieved using the current formulations of BS 7910 and the fatigue crack growth mean line for R~0.1 (Ref.4).

15

16

7. RECOMMENDATIONS

x It is recommended that further investigation be undertaken to incorporate in the fatigue crack growth formulation of BS 7910, methods to estimate the growth of the first observed through crack (based on N3) until a fully developed through crack (based on N*) is achieved. For this purpose, further fatigue tests will be required in order to measure the fatigue crack length and height during testing. Finite element analysis may also provide K solutions in order to estimate the crack growth ratios that should be applied in the N3 to N* interval.

x It is also recommended that further tests be carried out in order to study the fatigue crack shape development, which is essential to validate fatigue crack growth formulations developed within the N3 to N* interval.

x Behaviour is likely to be influenced by the wall thickness to diameter ratio. Further tests for tubes of different dimensions are therefore recommended in order to allow broader application of these findings.

x The results provide a limited statistical dataset and need to be considered further in conjunction with the wider data in the literature.

17

18

8. REFERENCES1 – Sharp J V, Stacey A, Wignall C M ‘Structural Integrity Management of Offshore Installations Based on Inspection for Through-Thickness Cracking’, OMAE 1998

2 – Lapwood D G ‘Pedigree of Steel used in the UKOSRP-I Programme’, SDR(1984), TWI Report No. 3460/12/77, August 1977.

3 – BS 7910:1999 (incorporating Amendment No.1): ‘Guide on methods for assessing the acceptability of flaws in metallic structures’

4 – King R N, Stacey A and Sharp J V: 'A Review of Fatigue Crack Growth Rates for Offshore Steels in Air and in Seawater Environments', OMAE 1996, Vol.III, pp.341-348.

19

20

Tab

le 1

Fa

tigue

test

ing

resu

lts

Spec

imen

N

omin

al S

tress

N

omin

al M

ean

Ran

ge

Stre

ss (M

Pa)

(MPa

) W

01-0

1+ 10

0 50

W

03-0

1**

100

50

W06

-01

150

75

W08

-01

150

75

W09

-01

150

75

W05

-01

200

100

W07

-01++

20

0 10

0 W

02-0

1 25

0 12

5 W

04-0

1 25

0 12

5

N2

N3 (

cycl

es)

N2/N

3 N

* N

* /N3

N4 (

cycl

es)

N4/N

3 (c

ycle

s)

2,88

3,08

0 -x

--x

--x

--x

--x

--x

-5,

092,

793

-x-

-x-

-x-

-x-

-x-

-x-

1,08

2,96

9 1,

614,

801

0.67

1 1,

708,

394

1.06

1,

728,

475

1.1

344,

162

498,

600

0.69

0 57

2,90

0 1.

15

584,

791

1.2

335,

323

1,34

0,29

1 0.

250

1,41

7,22

4 1.

06

1,44

2,57

4 1.

1 31

4,20

7 47

0,87

2 0.

667

495,

915

1.05

51

7,97

3 1.

1 62

1,93

5 63

6,61

3n

0.97

6 64

6,55

6 1.

02

668,

122

1.0

120,

000

137,

840

0.87

1 14

6,00

0 1.

06

149,

489

1.1

290,

900

386,

036

0.75

4 40

0,81

8 1.

04

403,

777

1.0

-x- D

ata

not a

vaila

ble

+ O

verlo

aded

. No

crac

ks w

ere

iden

tifie

d in

the

spec

imen

. Num

ber o

f cyc

les i

ndic

ate

end

of te

st.

** T

est s

topp

ed a

t the

num

ber o

f cyc

les i

ndic

ated

. No

crac

ks w

ere

iden

tifie

d in

the

spec

imen

.++

Cra

ck in

itiat

ion

not c

lear

ly id

entif

ied

on v

isua

l ins

pect

ion.

N2 v

alue

s est

imat

ed fr

om st

rain

gau

ge m

easu

rem

ent

n T

he n

umbe

r of c

ycle

was

est

imat

ed fr

om th

e pr

evio

us c

rack

size

mon

itorin

g be

fore

the

thro

ugh

crac

k w

as d

etec

ted.

21

Table 2 Internal and external measured crack length and correspondent fatigue cycles (all measures in

millimetres).

Specimen

W01-01

Position

Internal External

Crack length at N2

-x--x-

Crack length at N3

-x--x-

Crack length at N*

-x--x-

Crack length at N4

-x--x-

Weld/Parent Interface*

-x--x-

W03-01 Internal External

-x--x-

-x--x-

-x--x-

-x--x-

-x--x-

W06-01 Internal External

40 -x­

67 44

174 177

462 -x­

221 -x-

W08-01 Internal External

30 -x­

72 23

150 170

492 -x­

292 -x-

W09-01 Internal External

5 -x-

93+23 35

185 178

500 -x­

193 -x-

W05-01 Internal External

32 -x­

84 36

133 117

484 -x­

150 -x-

W07-01 Internal External

-x--x-

-x--x-

-x--x­

473 -x­

227 -x-

W02-01 Internal External

37 -x­

85 54

152 142

400 -x­

235 -x-

W04-01 Internal External

23 -x­

118 36

180 170

408 -x­

210 -x-

-x- Data not available

22

Table 3 Result of the fatigue crack growth from BS 7910, two stage fatigue crack growth curve.

Specimen N2 N2 crack

size (mm) N3,est N2/N3,est N* N*/N3,est N4est N4est/N3,est N4,est/N4

W01-01 2,883,080 N/A N/A N/A N/A N/A N/A N/A N/A W03-01 5,092,793 N/A N/A N/A N/A N/A N/A N/A N/A W06-01 1,082,969 40 1,277,681 0.848 1,708,394 1.34 1,304,785 1.02 0.75 W08-01 344,162 30 409,162 0.841 572,900 1.40 427,162 1.04 0.73 W09-01 335,323 5 749,323 0.448 1,417,224 1.89 781,323 1.04 0.54 W05-01 314,207 32 396,207 0.793 495,915 1.25 408,207 1.03 0.79 W07-01 621,935 N/A N/A N/A N/A N/A N/A N/A N/A W02-01 120,000 37 154,000 0.779 146,000 0.95 160,000 1.04 1.07 W04-01 290,900 23 342,900 0.848 400,818 1.17 350,900 1.02 0.87

N/A – not applicable

Table 4 Result of the fatigue crack growth from BS 7910, simplified fatigue crack growth curve.

N2 crack Specimen N2 size (mm) N3,est N2/N3,est N* N*/N3,est N4est N4est/N3,est N4,est/N4

W01-01 2,883,080 W03-01 5,092,793 W06-01 1,082,969 W08-01 344,162 W09-01 335,323 W05-01 314,207 W07-01 621,935 W02-01 120,000 W04-01 290,900

N/A – not applicable

N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 40 1,323,965 0.818 1,708,394 1.29 1,350,948 1.02 0.78 30 420,162 0.819 572,900 1.36 438,162 1.04 0.75 5 857,323 0.391 1,417,224 1.65 889,323 1.04 0.62

32 410,207 0.766 495,915 1.21 422,207 1.03 0.82 N/A N/A N/A N/A N/A N/A N/A N/A 37 160,000 0.750 146,000 0.91 166,000 1.04 1.11 23 350,900 0.829 400,818 1.14 357,900 1.02 0.89

23

APPENDIX A Material Certificates

APPENDIX C Weld Inspection Certificates

APPENDIX D Fatigue Test Certificates

APPENDIX E Engineering Critical Analysis

Printed and published by the Health and Safety ExecutiveC30 1/98

Printed and published by the Health and Safety Executive C0.06 08/04

ISBN 0-7176-2867-1

RR 224

78071 7 628674£20.00 9