PWHT Exemption

....

. . . . . . .

.

.

.

.

.

.

a

. .

..:.

..

.... .

.

.

. . ... . . . . . :. . . . . . . . . -

. . .

., .. . ., :... .,.. . . .. . .. .. . .. .. . .. . . . .

. .. . . By

..

.

. ..

:

. ..

..

..

. .

. .

.

..

.

.

R...H Leggatt, A.Muhammed, ,and M., Che./itani' :A. T,Smith .; ' ,: . .

. ..

'

. . ~.

.

.

. . .

. . .:,:.~. ..._ .. . . . . ..... .. .. .. .. .. .. . .

..

,-. . . . ...........

. :

. .

.

..'

.

.

.

. ,

.

. .

. . . . .. . .. .. :. . . .

'. "

. . .. . . . ., ., .- ;:,: .

::

. . ..

. . . . . . . . .

. . . . . . .. ... . . .

.

,

-

1' .;..

. . .. . .

.kL3

a a a a

.

,..

. :

..

.

.

.

.

.

. .

.

:@ IJ.

~.

.

.

.

..

.

... . ~.

. . . . .

...

~

.

.

.

.

.

.

.z

, ~

.

..

..

. . . . .

.

..

. ... . .. . . -. . . - . . . . .

B.

. . f = 3 'Z:.. . ... ..:

.

....:.........;..

....

.,

;;

.

.

.

.

.

.

. ,

.. .

.

. . . . .. . ..

.

.

.

.

. . . . . . .. . . :.

. . . . .

. . .

-

.

.

.

.

.

.

.

.

.. ,

.

@.

'4

This Research Report is for the exclusive use of subscribing members of TWI, and its content should not be communicated to other individuals or organisations without written consent. It is in the interest of all members to respect this confidence.

May 1999

67911999

Using fracture mechanics to claim exemption from PWHT four case studies

-

By R H Leggan, A Muhammed, A T Smith and M J Cheairani

No embargo

M'I, G m r n P* G-t A b i i k o n Gmbridgc CBI 6AL. United Kingdmn Telephone: +44 (0) 1223 891 162

T e k k +U(0)1223 892588

USING FRACTURE MECHANICS TO CLAIM EXEMPTION FROM PWHT- FOUR CASE STUDIES

CONTENTS TECHNOLOGY BRIEFING Background Objectives Approach Results and Discussion Main Conclusions Recommendations

1.

INTRODUCTION

1

2.

OBJECTIVES

2

3.

INDUSTRIAL CASE STUDIES

2

3.1.

CASEA: SPHERICAL PROPANE VESSEL 3.1.1. Background 3.1.2. Objective 3.1.3. Input Parameters 3.1.4. Engineering Critical Assessment (ECA) 3.1.5. Fracture Assessment Results 3.1.6. Discussion

3.2.

CASEB: STUBTO HEADER WELDREPAIR 3.2.1. Background 3.2.2. Objective 3.2.3. Input Parameters 3.2.4. Fracture Assessment Results 3.2.5. Discussion 3.2.6. Conclusions

3.3.

CASEC: TITANIUM ALLOYRISER 3.3.1. Background Objective 3.3.2. 3.3.3. Input Parameters 3.3.4. Fracture Assessment Results Discussion 3.3.5. 3.3.5.1. Technical justification for a relaxed PWHT procedure 3.3.5.2. Financial justification 3.3.6. Conclusions

PRAD No: 7308.0119911022.03 Copyright Q TWI 1999

12 12 13 13 14 14

14 15 15

USING FRACTURE MECHANICS TO CLAIM EXEMPTION FROM PWHT - FOUR CASE STUDIES

CONTENTS (contd) 3.4.

CASED: HIGHPRESSURE/HIGH TEMPERATURE SEPARATOR VESSEL 3.4.1. Background 3.4.2. Objective 3.4.3. Input Data 3.4.4. Engineering Critical Assessment (ECA) 3.4.5. Fracture Assessment Results 3.4.6. Discussion 3.4.7. Conclusions

4.

SUMMARY AND DISCUSSION OF CASE STUDIES 4.1. TECHNICAL CASEFOR EXEMPTION FROM PWHT AND FINANCIAL IMPLICATIONS

5.

CONCLUSIONS

6.

ACKNOWLEDGEMENTS

7.

REFERENCES

TABLES AND FIGURES

PRAD No: 7308.01/99/1022.03 Copyright Q TWI 1999


TECHNOLOGY BRIEFING Background Surveys of member companies conducted by TWI and EWI have shown that there is a strong demand for research aimed at reducing the requirement for post-weld heat treatment (PWHT). Current design codes for the design of pressure vessels, boilers and piping specify that PWHT is required if the thickness of the parts being welded exceeds a specified value. This value depends on the type of material being used, and varies from code to code. The use of a thickness criterion for PWHT provides a simple and direct method for determining whether PWHT is required. An alternative procedure for deciding whether PWHT is necessary to avoid the risk of failure by fracture is by conducting a fracture mechanics assessment using a recognised procedure such as that described in PD6493: 1991. A criterion for PWHT based on a fracture mechanics assessment is more complicated than a criterion based on thickness alone. It seems unlikely that designers, owners or certifying authorities would, in general, wish to abandon the thickness-based criteria in favour of a more complicated approach. However, there are many cases in which PWHT is required by the appropriate code, but may be considered to be unnecessary, excessively expensive, or impossible. In these cases, a fracture mechanics assessment may be used, subject to the agreement of the concerned parties, to determine whether PWHT is necessary for the avoidance of failure by fracture. Objectives

To illustrate how the fracture assessment procedures of PD6493:1991 may be used to make a case for exemption from PWHT. To provide examples of the technical and economic benefits which may be obtained using these procedures. Approach In order to demonstrate the potential benefits of using fracture mechanics to justify exemption from PWHT, TWI has performed a series of 'Industrial Case Studies'. Member companies which had expressed an interest in relaxation of PWHT requirements were invited to submit details of industrial applications in which they would wish to claim exemption from PWHT. A total of twelve cases were submitted, and four were selected for analysis. The need for PWHT was assessed with regard to avoidance of fracture and plastic collapse. Other failure mechanics such as fatigue, creep and stress corrosion cracking were not considered. The cases investigated were as follows:

PRAD No: 7308.01/99/1022.03 Copyright 0 TWI 1999

Page i

USING FRACTURE h1ECHANICS TO CLAIM EXEMPTION FROM PWHT - FOUR CASE STUDIES

Case A: Case B: Case C: Case D:

Spherical propane storage vessel, diameter 14m, thickness 37mm, A537 Class 1 steel. Stub-to-header repair weld, stub diameter 48mm, stub thickness IOmm, 2%CrMo steel. Titanium alloy riser, diameter 273mm, thickness 28mm. Repair of separator vessel, diameter 1830mm, thickness 34mm, SA516 Grade 70 steel.

Results and Discussion The structures were shown to be fit-for-purpose in the as-welded condition in three of the four cases studied (Cases A, B and D). In Case C, the titanium riser could not be shown to be fit-for-purpose in the as-welded condition, but the analysis could be used to determine what level of residual stresses would be acceptable, and hence to establish the heat treatment conditions. The costs of performing the analyses, including gathering the necessary data, were considered to be negligible compared with the potential cost savings in the first three cases. There was a moderate cost saving in the fourth case. Main Conclusions Fracture mechanics assessment provides a cost-effective method of investigating whether PWHT is necessary in order to avoid the risk of failure by fracture: the costs of performing the analyses are relatively modest, and in some cases, the costs saved if PWHT can be avoided are large. It was shown that the structures were fit-for-purpose in the as-welded condition in three of the four cases. For the titanium alloy riser, it was found that PWHT was necessary. A fracture mechanics analysis could be used as a basis for determining the heat treatment temperature. The chances of making a successful case for avoidance of PWHT are best with a good knowledge of the input parameters. In particular, assumptions regarding fracture toughness, reference flaw sizes and applied stresses can be crucial to the .. outdome ofjhe analysis.

-

Recommendations In cases in which PWHT is required by the appropriate code, but is considered to be unnecessary, excessively expensive, or impossible, a fracture mechanics assessment may be used to determine whether PWHT is necessary for the avoidance of failure by fracture. Consideration should also be given to the influence of heat treatment on avoiding other failure mechanisms, such as fatigue or stress corrosion cracking. Fracture mechanics assessments would be more reliable and easier to perform if design codes specified minimum fracture toughness (rather than Charpy) levels that should be achieved and reference defect sizes that should be detected.

Page ii


USING FRACTURE MECHANICS T O CLAIM EXEMPTION FROM PWHT - FOUR CASE STUDIES

1.

INTRODUCTION Surveys of member companies conducted by TWI and EWI have shown that there is a strong demand for research aimed at reducing the requirement for post weld heat treatment (PWHT). The following views were expressed: that the requirements for PWHT in current design and construction codes have not taken account of improvements in weldment toughness since the codes were originally written; that there are anomalies between different codes; and that there is great potential for cost savings if heat treatment requirements could be relaxed. Current design codes such as the BSI and ASME codes for the design of pressure vessels, boilers and piping and HSE guidance for the design of offshore installations' specify that PWHT is required if the thickness of the parts being welded exceeds a specified value. The limit depends on the type of material being used, and minimum design temperature, but the value varies from code to code. The use of a thickness criterion for PWHT provides a simple and direct method for determining whether PWHT is required. It has been in use for many years, and the current thickness criteria can be considered to have been validated by custom and practice. TWI are not aware of any failures which have been attributed to any inadequacy in the thickness criteria for PWHT. An alternative procedure for deciding whether PWHT is necessary to avoid the risk of failure by fracture is by conducting a fracture mechanics assessment using a recognised procedure such as that described in ~ ~ 6 4 9 3 : 1 9 9. 1The ~ use of this procedure is permitted in the British pressure vessel standard BS 5500: 1997' and in the HSE guidance for the design of offshore installations'. A general description of the use of PD6493 to justify exemption from PWHT is given in a previous papeS. The method is applicable to both new components and repair welds. The analysis given in this report is based entirely on avoidance of failure by fracture and plastic collapse. Consideration should also be given to the influence of heat treatment on avoiding other failure mechanisms such as fatigue and stress corrosion cracking. Fracture mechanics analysis is based on a consideration of the stresses or strains acting at critical locations in the structure, the local geometry, the mechanical properties, the size of flaws which may have escaped detection or been detected but left unrepaired, and the fracture toughness of the parent metal, weld metal and HAZ, as measured by the crack tip opening displacement (CTOD), stress intensity factor (K) or energy release rate (J). A criterion for PWHT based on fracture mechanics analysis is clearly much more complicated than a criterion based on thickness alone. It seems unlikely that designers, owners or certifying authorities would, in general, wish to abandon the thickness-based criteria in favour of a more complicated approach. Users would no doubt like to see a relaxation in the current thickness criteria, and there is some merit in the argument that the codes have failed to take account of improvements in toughness. Unfortunately, it is not possible to use fracture mechanics to justify a general relaxation or rationalisation of the thickness


Page 1


criteria. Any fracture-based assessment must take account of all the parameters listed above. If the thickness criterion were dependent on all these parameters, it would lose its main advantage: simplicity. However, there are many cases in which PWHT is required by the appropriate code, but may be considered to be unnecessary, excessively expensive, or impossible. In these cases, a fracture mechanics assessment may be used, subject to the agreement of the concerned parties, to determine whether PWHT is necessary for the avoidance of failure by fracture. Consideration should also be given to the influence of heat treatment on avoiding other failure mechanisms, such as fatigue or stress corrosion cracking. In order to demonstrate the potential benefits of using fracture mechanics to justify exemption from PWHT, TWI has performed a series of 'Industrial Case Studies'. Member companies which had expressed an interest in relaxation of PWHT requirements were invited to submit details of industrial applications in which they would wish to claim exemption from PWHT. A total of twelve cases were submitted, and four were selected for analysis. The four Industrial Case Studies are presented in Section 3 of this report, and discussed in Section 4. 2.

OBJECTIVES To illustrate how the fracture assessment procedures of PD6493:1991 may be used to make a case for exemption from PWHT. To provide examples of the technical and economic benefits which may be obtained using these procedures.

3.

INDUSTRIAL CASE STUDIES

3.1.1.

Background This case was provided by Company A, an engineering design and consulting firm. Several large spherical vessels have been commissioned for service as propane storage vessels. The size of the spherical vessels (14m ID) makes PWHT very difficult and expensive. It will be extremely beneficial if a case can be made for waiving the PWHT requirements for these spheres.

3.1.2.

Objective To evaluate the case for a PWHT waiver for the propane spheres using a fracture mechanics based approach.

Page 2

PRAD No: 7308.01/99/1022.03 Copyright O TWI 1999


3.1.3.

Input Parameters The propane spherical vessel is designed to BS 5500: 1 9 9 4 ~and built of steel plate strakes with some of the joints welded on site. The major structural dimensions and design details of the spherical vessel are given below: Parent plate material Internal diameter Wall thickness (varies) Design Pressure Proof Test Pressure / temperature Operating Pressure I temperature Average air temperature (outside) Minimum design temperature Specified minimum yield strength Tensile strength (specified minimum) Charpy energy (WM, HAZ, parent) Coefficient of thermal expansion, a Poisson's ratio, v Young's Modulus, E Welding processes NDT

A537 class 1 = 14000mm = 35.2 to 37.lmm = 19 barg (I .9N1mm2) = 24.5 barg ( 2 . 5 ~ l m m ~ ) l l 0 ~ ~ = 10.5 barg ( l . l ~ l m m ~ ) / 3 2 ~ ~ = 28°C = -46°C = 345Nlmm2 = 483Nlmm2 = 305 at -40°C minimum = 12 x 1O-~/OC = 0.3 = 2.07 x 1 0 ~ ~ l m m ~ SAW and SMAW 100% Radiography

The above information was used to calculate the relevant stresses and to estimate mechanical properties for the engineering critical assessment (ECA). 3.1.4.

Engineering Critical Assessment (ECA) 1~ using the TWI The ECA was carried out to the BSI ~ ~ 6 4 9 3 : 1 9 9procedures software Crackwise Version 2. Two types of analysis were performed. The first type was aimed at determining whether the vessel is fit-for-purpose in the as-welded condition. The fracture toughness value used in this set of analyses was derived from the specified Charpy energy requirement using a published Charpy-toughness (CV-K) correlation. It is prudent to cany out assessments to the PD6493 Level 1 procedures when using CV-Kcorrelations and this has been done for the test, design and operating conditions in this study. Where the first type of analysis did not give a clear indication of fitness-for-service based on the assumed fracture toughness, the second type of analyses was conducted. This was carried out to determine the critical toughness values required for avoidance of failure in the as-welded condition. As the toughness values obtained from correlations with Charpy energy tend to be very conservative, this second type of analysis gives a critical value that can be compared with fracture toughness data obtained from testing relevant vessel material. The analysis in this case was based on the PD6493 Level 2 procedures and an assumed reference flaw size representative of defects not likely to have been missed by NDT.

PRAD No: 7308.0 119911 022.03 Copyright 0 TWI 1999

Page 3


Further details on the input to the ECA are briefly outlined below: Component Geometry The analyses have been carried out for the main construction welds with the section details obtained from the engineering drawings provided. A thickness of 35.2mm and a width of 8600mm were used in the ECA. Primary Stresses The membrane stress o in the vessel due to internal pressure p was calculated for the test and design conditions using the equation o =pR/2t, where R and t are the radius and thickness, respectively, of the relevant component of the vessel. For the test condition, the pressure due to the hydrostatic head of water was added to the specified test pressure in calculating p and o. Local high stress regions such as those at supports, skirts, penetrations and nozzles were not considered in this analysis. Residual Stresses In the as-welded condition, SMYS magnitude residual stresses were assumed. However, for the Level 2 analysis, allowance was made for the relaxation of the residual stresses due to proof loading or primary stresses depending on which gave the greater relaxation. Stresses Due to Misalignment Allowance was made for a misalignment of 3.0mm between adjacent plates in accordance with BS 5500. The resulting bending stresses were computed using equations given in Appendix D of PD6493: 1991. Thermal Stresses Stresses due to temperature gradients across wall thickness were included in the ECA relating to the assessment of operating and design conditions. The average temperature outside the tank was given as 28OC. The resulting bending thermal stress ob was calculated using the equation given in Ref.6.

o*=

EaAT 2(1- v)

For a temperature gradient (AT) of 74°C at the minimum design temperature and the other assumed input data (see Section 3.1.3), this gives a bending stress of 1 3 1 ~ 1 m m(a~ smaller bending stress of about lOMPa resulted for the operating condition). Also, a thermal membrane stress was included in the ECA to allow for variation in the temperature at different vessel regions. Assuming the vessel to be restrained against expansion or contraction in two directions the stress om was calculated from the following equation6.

Page 4



om=-

EaAT (1 - v)

The variation in average temperature with location is expected to be much less than that assumed across wall thickness above. A value of 10°C was assumed for the design conditions resulting in a thermal membrane stress of 35~1mm'. No thermal stresses were included in the analysis for the proof test condition as no significant gradient is expected to have developed during the short duration of the hydrotest. Fracture Toughness The specified Charpy encrgy requirement for the vessel material was 305 (min.) at -40°C. It is assumed that this requirement applies to all parent steels and welds. The Charpy-fracture toughness correlations given in the draft BS 7910" (Annex K) were used in estimating the fracture toughness values. BS 7910 will replace PD6493 and is scheduled to be published in 1999. The correlations of Annex K include more recent developments and have therefore been used in preference to those given in PD6493: 1991. First, fracture toughness was estimated assuming transitional behaviour on the basis of the Master Curve approach. The basic equation for this is:

where K,,, is in ~ ~ a d m T = T27~ = B =

Pf

=

temperature at which K,,, is to be determined 275 Charpy transition temperature (OC) material thickness probability of failure (5% recommended by BS 7910)

The above equation was applied to the three temperatures of interest, that is, -46"C, 10°C and 32°C for design, proof test and operating conditions respectively. From the 30J (min) energy requirement at -40°C, the 275 temperature was calculated as -42.I0C using Table K1 of draft BS 7910 Annex K. Also the thickness B was taken as 13.2mm from the input data. The calculated L,(for Pr = 0.05) values were 2175, 4814 and 6 9 0 5 ~ m m " ' ~at -46"C, 10°C and 32"C, respectively. Ideally the estimates for 10°C and 32°C should be checked against L,estimates for fully ductile behaviour. This is not necessary here as the assessment for fimess-forservice is governed by the design condition (i.e. 46OC).


Page 5


Assumed Reference Flaw In order to determine the minimum toughness required to avoid failure in the aswelded condition, a reference flaw is required for the analysis. The vessel is built to BS 5500:1994 with 100% radiography (RT) of the welds. BS 5500 radiographic acceptance levels require that all planar defects found must be repaired. However, detection capability can be low for planar flaws with tight gape when using radiography. It would therefore be reasonable to perform additional ultrasonic inspection in a case concerned with waiving post-weld heat treatment. Assuming the ultrasonic inspection (UT) is performed to a good standard, a reference flaw may be determined from the NDT capability given in Ref.7, see Table 1. For the relevant joint thicknesses, the document quotes a surface flaw 2mm deep by 8mm long as being typically within the detectability of manual ultrasonics. This implies that flaws of this size should be detectable, but may not be sized accurately. These reference NDT dimensions may be used for an ECA where no flaws have been found or any flaws found have been repaired. These dimensions have been adopted for the reference flaw in the present analyses. For actual cases, issues of sizing capability of UT must also be considered. 3.1.5.

Fracture Assessment Results The results of the Engineering Critical assessments are presented below. Details of the Crackwise output are given in Appendix A. Tolerable Surface Flaw Sizes The results of the analyses based on PD6493:1991 Level 1 procedures are summarised in Fig.1-3 for the design, proof test and operating conditions. The results show that the as-welded vessel is satisfactory (i.e. 2mm deep by 8mm long surface flaws are tolerable) under the conditions considered. The design condition is the most onerous of the three cases as illustrated by the relative proximity of the assessment point to the failure assessment line. However, it is likely that the actual margin of safety is higher than that suggested by the analysis, given the level of conservatism in the Charpy-K correlations and in the Level 1 FAD used in this case.

3.1.6.

Discussion Technical Justification for Avoidance of PWHT The results show that the assumed reference surface flaw (2mm x 8mm) is tolerable in the as-welded condition. Flaws of this size should be detectable using a good manual ultrasonics inspection procedure. This provides technical justification for avoidance of PWHT.

Page 6


USING FRACTURE MECHANICS T O CLAIM EXEMPTION FROM PWHT- FOUR CASE STUDIES

It should however be noted that this study has considered only the main constructional welds. Other details such as attachment welds should either be assessed using the fitness-for-service approach adopted here or the attachment welds should be completed and heat treated prior to final assembly. Financial Justification The cost of PWHT of the spherical vessels was estimated to be about f I00 000 by the client. This can be compared with the costs of data collection, analyses and fracture toughness measurement which will be a small proportion of that cost (around 10%). The use of a fracture mechanics procedure to waive PWHT would therefore represent a significant cost saving. Conclusions The analyses conducted on the basis of Charpy energy requirement and Charpytoughness correlation show that the spherical vessel can be considered fit-forservice in the as-welded condition. On the basis of financial data provided by the client, the cost of conducting analysis and testing for a PWHT waiver is negligible when compared to the cost of a PWHT programme.

3.2.1.

Background This case together with background information and basic data have been provided by company B, a large power generator. The case concerns a stub to header weld repair. The parent material involved, a 2%CrMo steel type HFS 622, has been selected as one of the steels in widespread use for high temperature steam headers and drums. High temperature headers in conventional coal and oil fired power plant collect steam from the boiler superheater and reheater sections. A typical header may collect steam from several hundred separate boiler tubes. The header is a long cylindrical vessel mounted in the 'dead space' above the furnace. The tubes emerge vertically from the fumace and pass through a gas seal into the dead space. Each tube is welded to a shorter length of tubing 'the antler' which is of a similar cross section, but bent as required to connect to the header. The antler is in turn welded to a short stub tube, which is welded directly to the header. Short stub tubes are welded on to the header in the fabrication works. Hence, all the stub to header welds can be post weld heat treated together at the same time as the header structural welds, commonly using a large furnace to heat treat the complete header or a large header section in a single operation. Short stub tubes allow the component to be transported to site without undue difficulty, and the stub to antler welds can then be made on site. Because these are relatively thin section, their post-

PRAD No: 7308.0119911022.03 Copyright 0 TWI 1999

Page 7

USING FRACTURE MECHANICS TO CLAlhl EXEMPTION FROM PWHT- FOUR CASE STUDIES

weld heat treatment is usually not required to BS 2633 when low alloy steels such as 1CrMo or 2%CrMo are employed. PWHT of the stub to header welds in the fabrication works is not excessively difficult or expensive. However, PWHT of a single stub to header replacement on site is cumbersome. Such PWHT requires uniform heating of a cylindrical band around the header circumference. This is complicated by the many tubes protruding from the header, and the operation may cause an expensive delay to a breakdown repair outage. It is, nevertheless, commonly camed out. However, in some emergency situations, temporary repairs without PWHT have been permitted and have operated satisfactorily until permanent repair could be undertaken. 3.2.2.

Objective To determine whether a single stub to header repair weld is fit-for-purpose in the aswelded condition.

3.2.3.

Input Parameters Company B has provided information on service stresses (FE data on operating stresses and additional thermal stresses), material properties (including toughness data), and maximum dimensions of flaws which might be present. Geometry of Header and Stub Header inside diameter = 280 +/- 3mm Header minimum thickness = 52mm Stub outside diameter = 48.3mm Stub thickness = IOmm Design temperature = 535°C Operating temperature < 535OC Assumed Flaw Types and Locations The following hypothetical flaws have been considered (see Fig.4): i. ii.

...

111.

Surface and embedded longitudinal flaws in the header at the weld toe Surface and embedded longitudinal flaws in the stub at the weld toe Embedded transverse flaws in the weld.

Primary Stresses The primary stresses have been estimated from finite element data provided by company B in the stub at the weld toe (Lines 1 and 4), in the weld (Lines 2 and 5) and in the header at the weld toe (Lines 3 and 6), see Fig.4. These stress distributions have been linearised excluding peak stresses, which are associated with the presence of the weld and allowed for in the analyses via the parameter Mk. This is a dimensionless stress intensity magnification factor which is a function of

Page 8

PRAD No: 7308.01/99/1022.03 Copyright Q T W I 1999


the weld geometry and local weld toe profile (see Appendix E in BSI ~ ~ 6 4 9 3 : 1 9 9 1 ' )The . stress linearisation has given membrane and bending stresses in the transverse direction (stresses perpendicular to the weld) and in the longitudinal direction (stresses parallel to the weld) shown in Table 2. Given that for each postulated flaw, two stress distributions may be relevant (e.g. stresses associated with Lines 1 and 4 for stub flaws), fracture analyses have been performed for both sets of stresses, and the most conservative result has been adopted. Thermal Stresses Thermal stresses due to a thermal shock load have been estimated from finite element data provided by company B at the weld toe and across the thickness of the header and stub. The shock load is a down shock on the inner surface of 100°C in one minute, which is regarded as a reasonable worst case. The stress distributions have been linearised, giving membrane andlor bending stresses in the transverse direction (stresses perpendicular to weld) and in the longitudinal direction (stresses parallel to the weld) shown in Table 3. The thermal stresses acting on the postulated flaws are compressive. Their presence reduces the magnitude of the total stresses (i.e. sum of applied, residual and thermal stresses) and results in a lower total crack driving force than that associated with applied and residual stresses alone. Therefore, such thermal stresses are beneficial, but given that they occur only as a result of a thermal shock load, such benefit can not be used under normal service loading. Consequently, the fracture analyses have been performed assuming no thermal stresses. Welding Residual Stresses In accordance with the recommendations of PD6493:1991, residual stresses in the as-welded condition have been assumed to be uniform across the thickness as follows: For longitudinal flaws at the weld toe in the header or stub, the welding residual stress is assumed to be the lesser of the room temperature yield strengths of the weld or parent metal, i.e. 2 7 5 ~ / m m * . For transverse flaws in the weld, the welding residual stress is assumed to be equal to the room temperature yield strength of the weld, i.e. 370~lmrn*. No allowance has been made for the effects of proof testing on the magnitude of welding residual stresses.


Page 9

USING FRACTURE MECHANICS TO CLAIM EXEMPTION FROM PWHT

- FOUR CASE STUDIES

Mechanical Properties Parent metal tensile properties at room temperature: c~ys= 275Nlmm2 (SMYS) (JTS = 490N/mm2 (SMTS) E = 2 0 7 0 0 0 ~ l m m(estimated) ~ Parent metal tensile properties at operating temperature (assumed = 535°C): oys = 174Nlmm2 07s = 209N/mm2 (estimated) ~ based on Table 3.6.3 in BS 5500: 1997') E = 1 7 0 0 0 0 ~ 1 m m(estimated Weld metal tensile properties at room temperature:

The above yield and tensile strength values are basically the specified minimum values and these were used in the ECA. The actual values which are likely to be higher were not known, so no advantage could be taken of these in the ECA. However, the loss of this benefit of higher yield strength is likely to be offset by the use of the specified minimum value in estimating residual stresses (see above). Toughness Based on a review by company B of available data relevant to the parent metal, weld metal and HAZ, the toughness expressed in terms of KI, has been assumed equal to 3 1 6 2 ~ 1 m m " ~at the operating temperature. This toughness value was provided by Company B as an appropriate lower bound. Flaw Dimensions According to company B, a full volumetric inspection of the weld repair is considered difficult to cany out. Normally, visual and magnetic particle inspection are applied, and if considered necessary, ultrasonic testing (UT) can be used to give some assurance against flaws extending into the header. However, UT would not be considered to provide a complete inspection. Given the above, it has been assumed that only visual and magnetic particle inspections are applied. Therefore, surface breaking flaws can be discovered but not embedded flaws. According to company B, an unlikely but plausible embedded flaw height might be up to 12mm. This may be the height of a root flaw which has extended as a hydrogen crack in the weld metal and HAZ, mainly below the header outer surface. Such a flaw may be either longitudinal or transverse with regard to the welding direction. In both cases, the flaw may be inclined with respect to the through thickness direction of the header (if flaw is in header) or stub (if flaw is in Page 10



stub). For the purpose of the ECA, all flaws have been considered parallel to the through thickness direction of the header or stub. Longitudinal flaws have been considered to have a maximum length equal to the weld toe circumference on the header or stub. Dimensions of transverse flaws have been considered limited by the width of the weld. The matrix of flaws considered is shown in Table 4.

3.2.4.

Fracture Assessment Results The hypothetical flaws (listed in Appendix B) have been assessed using the Level 2 procedures of BSI PD6493:19912 with TWI software 'Crackwise 2'. PD6493:1991 uses flat plate solutions for the stress intensity factor and net section stress. These are, respectively, the solutions of Newman and ~ a j u ' , and Willoughby and ~ a v e ~ ~ . These solutions are know to be conservative for flaws in circumferential configurations. The Newman and Raju stress intensity factor solutions apply to flaws with a maximum length equal to half the plate width. Due to this restriction, the 'plate width' has been assumed to be twice the circumference of the stub for all the flaws considered, so that longitudinal flaws which have a length equal to the weld toe circumference, can be evaluated. Increasing the plate width dimensions leads to conservative solutions. For each of the flaws considered, an initial analysis has been conducted to establish whether or not the flaw is acceptable in the as-welded condition. If the flaw is acceptable, its presence is considered not to affect the fitness-for-purpose of the repair weld. If the flaw is unacceptable, an additional analysis has been carried out in order to calculate the critical flaw height assuming that the length is constant. All the header flaws, weld flaws, and one of the stub flaws (embedded, see Table 4) have been found acceptable. The sizes of these flaws have been chosen pessimistically as discussed above. The height of the surface flaw in the stub (see Table 4) has been established from a 'critical parameter analysis', i.e. it is the critical flaw height. Results of the analyses are given in Appendix B. Note that creep at operating temperatures has not been considered for the present analyses.

3.2.5.

Discussion Technical Justification for Exemption from PWHT The results in the previous section indicate that the embedded flaws assumed to exist in the header, weld, and stub of the weld repair in the as-welded condition are acceptable, i.e. are non-critical in terms of fracture and plastic collapse. The sizes of these flaws have been chosen pessimistically to allow for the possibility that such flaws may not be detected, since only visual and magnetic particle inspections are camed out. The 12mm deep surface flaws assumed to exist in the header are also acceptable. The critical height of a surface flaw in the stub, with a length equal to the weld toe


Page 11


circumference, is 5.3mm. If the minimum surface flaw height that can be reliably detected using visual or magnetic particle inspections is less than the tolerable height, i.e. 5.3mm, larger unacceptable flaws (height > 5.3mm) can be detected and dealt with, and it may be concluded that non-detectable surface flaws do not threaten the fitness-for-purpose of the weld repair in the as-welded condition. Based on the above and assuming that no other mechanisms, such as creep fatigue, may lead to extension of the original flaws, it is concluded that the weld repair is fitfor-purpose at room temperature under operating loading in the as-welded condition. Financial Justification It has been shown that the case for avoiding PWHT can be technically justified from a fracture and plastic collapse point of view. The cost of this analysis is likely to be negligible in comparison with the total cost associated with canying out PWHT on site which is cumbersome and may be excessively expensive.

3.2.6.

Conclusions On the basis of the data and assumptions adopted in the analysis, the stub to header weld repair may be considered fit-for-purpose in the as-welded condition provided that surface breaking flaws of height greater than 5.3mm can be reliably detected.

3.3.1.

Background This case was provided by company C, a metals manufacturer. Risers are used to transmit oil from the wellhead, located at the seabed, to a terminal such as a single point mooring, located at sea level. The riser needs to have a low elastic modulus to allow for movement and be relatively light to reduce the static load. Titanium alloys have been proposed as a suitable material because of its excellent mechanical properties and corrosion resistance. Risers are currently manufactured by welding sections together prior to being lowered over the side of a purpose built construction barge. There is currently a requirement that the construction welds be post weld heat treated. ECA can be used to investigate if the riser is fit-for-purpose in the as welded condition or to quantify the level of residual stress the riser will tolerate and still be fit-for-purpose. The PWHT procedure can then be adjusted to obtain the level of residual stress required thereby avoiding the unnecessary cost of full PWHT. The ECA was conducted in accordance with BSI PD6493:1991 procedures. Although the document is specifically aimed at welded fabrications in ferritic and austenitic steels, the scope extends to titanium alloy components such as in this case.

Page 12



3.3.2.

Objective T o determine whether the riser is fit-for-purpose in the as-welded condition, or if not, what level of residual stress in the weld is acceptable.

3.3.3.

Input Parameters The following analysis is based on a riser of dimensions: Internal diameter = 216.8mm External diameter = 273mm Thickness = 28.lmm The following information was provided by company C. Primary Stresses The ruling case is where the riser is subject to combined axial force and pressure forces of 1062kN and a bending moment of 651kNm. Primary membrane and bending stresses are calculated to be

w

Bending stress = 535N/mm2 Membrane stress = 56Nlmm2

All welds are machined flat and there are no additional stresses due to misalignment. Residual and Thermal Stresses In the as-welded condition, a peak residual stress value of 620Nlmm2 has been supplied. This is less than the yield strength of the titanium. The residual stress is assumed to be constant through the thickness of the riser. Allowance has been made for residual stress relaxation due to prior loading as per PD6493:1991. Thermal stresses are assumed to be negligible. Mechanical Properties These have been provided by company C as:

It is assumed here that the Gtvalue supplied is the appropriate value for both parent material and welds.

PRAD No: 7308.01/99/1022.03

Copyright 0 TWI 1999

Page 13


Flaw Dimensions The assumed flaw dimensions are for a circumferential surface breaking flaw. They have been specified by company C, as 12.7mm long and 1.5mm deep. These dimensions are based on the predicted depth of a fatigue flaw after sixty years service assuming an initial flaw size of 12.7mm (%") long and a depth 5% of the wall thickness (1.4mm in the present case). Company C have stated that any initial defects of the size quoted can be detected after fabrication. 3.3.4.

Fracture Assessment Results The case discussed above was analysed using the Level 2 procedure outlined in PD6493:1991 with the computer software package 'Crackwise 2'. The stress intensity factor given by Newman and ~ a j u was ' used, together with the net section stress solution given by ~astner''. An initial analysis was conducted to examine if the riser could be judged to be fitfor-purpose in the as-welded condition (Case Cl). A sensitivity analysis was then done to determine what level of residual stress could be tolerated in the riser weld for the riser to be fit-for-service (Case C2). Further sensitivity analyses were made to investigate the influence of assumed fracture toughness value (Case C3). Results are given in Appendix C and Fig.5 to 7.

3.3.5.

Discussion

3.3.5.1. Technical justification for a relaxed PWHT procedure Proposed Avoidance of PWHT Analysis of this case (Fig.5) shows that the riser is not fit-for-service for the assumed input parameters in the presence of as-welded levels of residual stress. This assessment assumes that the as-welded residual stress is constant through the section thickness and additional analysis of the residual stress distribution could possibly result in a less conservative assessment. The results are strongly influences by the assumed fracture toughness value (see Fig.6), and the level of residual stress (Fig.7). If testing of relevant parent pipe and weld material could demonstrate a fracture toughness value of 3145~1mm"'~(Case C3) at the relevant temperature; then the riser could be shown to be fit-for-purpose. Alternatively, acceptable levels of residual stresses could be determined, see below.

Page 14



Determination of Acceptable Level for Residual Stress The location of the defect assessment loci on the failure assessment diagram is a function of the level of residual stress. Using a sensitivity analysis it is possible to determine the maximum level of residual stress for the riser to be fit-for-service. This is shown in Fig.7. The maximum level of residual stress for the riser to be fitfor-purpose was determined as 207N/mm2. This level of residual stress is 33% of the assumed as-welded level of residual stress. At present, detailed information on the relationship of PWHT procedure to residual stress levels is unavailable. Experimental trials would therefore be needed to determine if these levels of residual stress are attainable and what PWHT procedure was appropriate. If this level of residual stress is unattainable then the riser cannot be judged as fit-forservice.

3.3.5.2. Financial justification For this case, the primary consideration is the technical justification for fitness for service. It was shown that the case for avoiding PWHT cannot be upheld for the input data provided. Hence, the considerable savings associated with the elimination of PWHT cannot be achieved for the conditions analysed. Improvements may be possible if actual fracture toughness data could be obtained to show that K,,,>3145~/mm'~~.It may also be possible to achieve some productivity gains and cost savings if the results can be used to justify a faster or more efficient PWHT cycle. The cost of any input parameter refinement and subsequent analysis is a small proportion of the total cost involved with the PWHT during installation of titanium risers.

3.3.6.

Conclusions On the basis of the information provided above, the titanium riser cannot be shown to be fit-for-service unless actual fracture toughness values can be shown to exceed 3 1 4 5 ~ m m " ' ~ or the residual stresses are reduced to a maximum of 207N/mm2. Without better toughness data, further work would be required to determine the PWHT conditions necessary to achieve the above level of residual stress required for this operation.

3.4.1.

Background This case was provided by company D, an international oil company. It involves a high pressurethigh temperature (HPHT) separator vessel already in use. The vessel was fabricated in 1981 without PWHT. However, cracks were later found, repaired and then post weld heat treated in 1989. The purpose of this study is to determine if further PWHT can be avoided in the event that repairs are required in the future.


Page 15


3.4.2.

Objective To determine whether the HPHT vessel would be fit for continued use after repair without post weld heat treatment.

3.4.3.

Input Data The vessel was designed and built to ASME VIII Div. 1. Details of the input data for the assessment are outlined below Material Data Parent plate material SA516 Gr 70 = 6'0" (1 829mm) Internal diameter Wall thickness = 1.35" (34mm) = 893 psi ( 6 . 2 ~ / m m ~ ) / 2 4 " ~ Test pressureltemperature = 530 psi ( 3 . 7 ~ 1 r n m ~ ) / 1 2 7 ~ ~ Operating pressureltemperature SMYS = 38 ksi (262N/mm2) = 70 ksi (483~lmm') Tensile strength = 2644NmrnJi2) Fracture toughness (parent metal, J) = 0.19 ksi-in (K) = [JE Fracture toughness (Hz environment), K = 70 ksidin = 2 4 3 4 ~ m m ' ~ ' ~ Welding processes repair welds by SMAW NDT 100% Radiography after fabrication, MT and UT in-service (crack sizing)

3.4.4.

Engineering Critical Assessment (ECA) The ECA was carried out to BSI ~ ~ 6 4 9 3 : 1 9 9Level 1 ~ 2 procedures using TWI software Crackwise 2. It is assumed that the vessel was fabricated using both longitudinal and circumferential seam welds. Both welds were assessed under service condition with allowance made for proof testing. Further details on the input to the ECA are briefly outlined below: Primary Stresses The primary membrane stresses on the seam welds due to internal pressure were calculated using standard vessel formulae. The resulting stresses are 49MPa and 97MPa for the girth and longitudinal seam welds respectively. The equivalent stresses under test condition were calculated as 82MPa and 164MPa for the girth and longitudinal seam welds respectively. No consideration was given to stress raisers at nozzles or supports in this particular case but their effect could be readily included if the relevant information was made available. Residual Stresses Yield magnitude residual stresses were assumed in all analyses. Allowance was also made for relaxation of residual stresses due to proof loading and interaction with primary stresses where applicable.

Page 16

PRAD No: 7308.01/99/1022.03

Copyright O TWI 1999


Stresses Due to Misalignment Construction tolerance limits specified in the 1995 ASME VIII Div.1 (see Section UW-33) allows a maximum eccentricity of 118" (3.2mm) for the plate thickness (34mm) of interest. This amount of eccentricity was included in the ECA with the resulting bending stresses calculated within Crackwise. Thermal Stresses No thermal stresses were included in the ECA. Fracture Toughness The minimum toughness (2434~mm.'") specified by the client was that for a hydrogen environment at the operating temperature. It is assumed for the purpose of this report that this value is representative for the environment and possible flaw location (parent steel, HAZ or weld) of concern. In practice, it will be necessary to perform tests to simulate service exposure to enhance the confidence in the toughness value employed in the assessments. Assumed Flaw Sizes It is believed that the welds were inspected by ultrasonics (UT) following the repairs. The IIW' document on fitness-for-purpose assessment was used to estimate the reference flaw not likely to have been missed by manual UT. For the relevant plate thickness (34mm), the minimum detectable flaw dimensions quoted in the document (see Table 1) is a surface breaking flaw 2mm deep by 8mm long. These dimensions were used for all the analyses as a typical size which needs to be tolerated in the as-welded conditions to allow a PWHT waiver. Adopting these dimensions implies that either no defects were found by NDT or any defects found were repaired.

3.4.5.

Fracture Assessment Results The results of the engineering critical assessment (ECA) are summarised in Fig.8-9. The results show that the girth and longitudinal welds are fit-for-service in the aswelded condition. Details of the Crackwise calculations are given in Appendix D.

3.4.6.

Discussion Technical Justification for Avoidance of P W H T The ECA provides evidence that further post weld heat treatment can be avoided. The analysis assumes that no further crack growth due to environment or loading history occurs in service. It is also assumed that any environmental factors contributing to the initial cracking has not led to any toughness reduction below the value (2434~mm"") used in the ECA.


Page 17

USING FRACTURE MECHANICS TO CLAIM EXEMPTION FROhl PWHT - FOUR CASE STUDIES

Financial Justification For this case the estimated cost of undertaking one local repair weld PWHT is of an order similar to that of canying out the PWHT waiver ECA. Therefore, the analysis in this case would represent no significant cost saving. The savings would be much greater compared with the cost of multiple local PWHT or other potential alternatives, such as vessel replacement or part replacement with PWHT. Also, the time cost of PWHT may include loss of production in some cases, thereby making a waiver ECA very worthwhile.

3.4.7.

Conclusions The analyses show that the vessel is fit-for-service in the as-welded condition. On the basis of the financial data provided by the client, using a fracture mechanics argument to justify local PWHT exemption of a single repair weld represents no significant cost saving. However, if canying out the PWHT involved loss of production, the true cost would be significantly higher thereby making a waiver ECA more attractive.

4.

SUMMARY AND DISCUSSION OF CASE STUDIES

4.1.

TECHNICAL CASEFOR EXEMPTION FROM PWHT AND FINANCIAL IMPLICATIONS The conclusions from the four case studies are summarised below, in all cases these are based on the assumption that the input parameters used are appropriate. Most of these were supplied by the member companies, and not validated by the authors. The conclusions below should not, therefore, be applied in any general sense to other welded structures and components. Case A The analyses conducted on the basis of Charpy energy requirement show that the spherical vessel can be considered fit-for-service in the as-welded condition. This suggests a good margin of safety against fracture in the as-welded condition given that Charpy toughness correlations tend to be very conservative. On the basis of financial data provided by the client, the cost of conducting analysis and testing for the PWHT waiver is marginal when compared to the cost of a PWHT programme.

Page 18

PRAD No: 7308.01199/1022.03 Copyright Q TWI 1999


Case B On the basis of the data and assumptions adopted in the analysis and assuming that no crack extension occurs due to fatigue andlor creep, the stub to header weld repair may be considered fit-for-purpose with respect to fracture and plastic collapse in the as-welded condition provided that surface breaking flaws of height greater than 5.3mm can be reliably detected. The cost of this analysis is likely to be negligible in comparison with the total cost associated with carrying out PWHT on site which is cumbersome and may be excessively expensive. Case C On the basis of the information provided above, the titanium riser cannot be shown to be fit-for-service unless actual fracture toughness values can be shown or) the residual stresses are reduced to a to exceed 3 1 4 5 ~ m m " ' ~( 9 9 . 5 ~ ~ a d m maximum of 2 0 7 ~ 1 m m ~ . Without better toughness data, further work would be required to determine the PWHT conditions necessary to achieve the above level of residual stress required for this application. The considerable savings associated with the elimination of PWHT cannot be achieved for the conditions analysed. It may be also possible to achieve some productivity gains and cost savings if the results can be used to justify a faster or more efficient PWHT cycle. The cost of any input parameter refinement and subsequent analysis is a small proportion of the total cost involved with the PWHT during installation of titanium alloy risers. Case D On the basis of the input data provided, the analyses show that the vessel is fitfor-service in the as-welded condition. For this case the estimated cost of undertaking one local repair weld PWHT is of an order similar to that of carrying out the PWHT waiver ECA. Therefore, the analysis in this case would represent no significant cost saving. The savings would be much greater compared with the cost of multiple local PWHT or other potential alternatives, such as vessel replacement or part replacement with PWHT. Also, the time cost of PWHT may include loss of production in some cases, thereby making a waiver ECA very worthwhile. In summary, the structures were shown to be fit-for-purpose in the as-welded condition in three of the four cases studied (Cases A, B and D). In Case C, the titanium riser could not be shown to be fit-for-purpose in the as-welded condition,


Page 19


but the analysis could be used to determine what level of fracture toughness or residual stresses would be acceptable. The costs of performing the analyses, including gathering the necessary data, were considered to be negligible compared with the potential cost savings in the first three cases. In the fourth case, there was negligible cost savings compared to a single repair weld PWHT.

The general conclusion from this work is that fracture mechanics assessment provides a cost-effective method of investigating whether PWHT is necessary: the costs of performing the analyses are relatively modest, and in some cases, the costs saved if PWHT can be avoided are large. A common problem that is encountered when performing fracture mechanics assessments is the difficulty in determining or selecting suitable values for some of the input variables. In particular, it is often difficult to decide an appropriate value for the size of defects which may be present in the structure and have escaped detection. Fracture toughness values of actual parent and weld material are often unavailable, but this parameter is often very crucial to the successful outcome of the ECA. If material extraction from the actual structure is impossible, weld procedure review and weldment simulation with subsequent testing can be used to determine appropriate input values. If no fracture toughness data are available and cannot be obtained, then estimated values are used based on a correlation between toughness (CTOD or K) and impact energy (Cv). Values of toughness obtained by this method tend to be very conservative. Fracture mechanics assessments would be more reliable and easier to perform if design codes specified minimum fracture toughness levels to be achieved and reference defect sizes to be detected. 5.

CONCLUSIONS Four industrial case studies exploring the benefits of using fracture mechanics analysis as the basis for claiming exemption from PWHT have been presented. The need for PWHT was assessed with regard to avoidance of fracture and plastic collapse. Other failure mechanisms such as fatigue, creep and stress corrosion cracking were not considered. The cases investigated were: Case A Case B: Case C:

Page 20

Spherical propane storage vessel, diameter 14m, thickness 37mm, A537 Class 1 steel. Stub-to-header repair weld, stub diameter 48mm, stub thickness lOmm, 2GCrMo steel. Titanium alloy riser, diameter 273mm, thickness 28mm.



Case D:

Repair of separator vessel, diameter 1830mm, thickness 34mm, SA516 Grade 70 steel.

Fracture mechanics assessment provides a cost-effective method of investigating whether PWHT is necessary in order to avoid the risk of failure by fracture: the costs of performing the analyses are relatively modest, and in some cases, the costs saved if PWHT can be avoided are large. It was shown that the structures were fit-for-purpose with respect to the avoidance of fracture and plastic collapse in the as-welded condition in three of the four cases (Cases A, B and D). For the titanium alloy riser, (case D), it was found that PWHT was necessary unless fracture toughness values determined on the actual weld procedure exceed the value assumed in the analyses. Alternatively, fracture mechanics analyses could be used to support the development of an appropriate PWHT procedure. The chances of making a successful case for avoidance of PWHT are best with a good knowledge of the main input parameters. In particular, assumptions regarding fracture toughness, reference flaw sizes and applied stresses can be crucial to the outcome of the analysis. Indeed, fracture mechanics assessments would be more reliable and easier to perform if design codes specified minimum fracture toughness levels that should be achieved and reference defect sizes that should be detected.

6.

ACKNOWLEDGEMENTS The authors are grateful to all the member companies who responded to our initial survey, and in particular to the company representatives who gathered the data for the case studies. The work described in this report was carried out within the TWI Core Research Programme, funded by the Industrial Members of TWI.

7.

REFERENCES 1 UK Department of Energy: 'Offshore installations: Guidance on design and

construction,' HMSO.

2 BSI PD6493:1991: 'Guidance on methods for assessing the acceptability of flaws in fusion welded structures'. BSI London, 1991.

3 BS 5500:1997: 'Specification for unfired fusion welded pressure vessels'. British Standards Institute, 1997. 4 Smith A T: 'Avoid post-weld heat treatment Bulletin, NovemberIDecember 1996, 119-122.


-

use fracture mechanics'. TWI

Page 2 1


5 BS 5500:1994: 'Specification for unfired fusion welded pressure vessels'. January 1994.

6 Spence J and Tooth A S (Ed): 'Pressure vessel design-concepts and principles'. 1992. 7 IIW: 'Guidance on assessment of the fitness-for-purpose of welded structures' Draft for development, IIWIIIS-SST-I 157-90, 1990. 8 Newman J C and Raju I S: 'Stress-intensity factor equations for cracks in threedimensional finite bodies subjected to tension and bending loads'. NASA Technical Memorandum 85793, April 1984. 9 Willoughby A A and Davey T G: 'Plastic collapse at part wall flaws in plates'. ASTM STP 1020,390-409, 1989.

10 Kastner K, Rohrich E, Schmitt W and Steinbuch R: 'Critical crack sizes in ductile piping'. Int J Press Ves and Piping 9, 197-2 19, 1981. 11 BS 7910:1998 (Draft): 'Guide on methods for assessing the acceptability of flaws in fusion welded structures'. 1998

Page 22

PRAD No: 7308.01/99/1022.03

Copyright O TWI 1999


Table 1 Typical detectable flaw dimensions using ultrasonic testing (Reproduced from IIWIIIS Guidance SST-1157-90')

Imperfection fully

Notes: (1)

Means that detection is at the 'full skip' position, i.e. where the beam is reflected off the back surface and up the underside of the scanning surface. Imperfections immediately under the probe cannot usually be detected if they do not extend more than 3mm down.

(2 )

Assuming that the back surface is parallel to the scanning surface so that the comer effect can operate.

USING FRACTURE MECHANICS T O CLAIM EXEMPTION FROM PWHT- FOUR CASE STUDIES

Table 2 Membrane and bending stresses in stub to header weld region (Fig.6, Case B)

Table 3 Thermal membrane and bending stress components in stub to header weld (Case B) i

Stress Component, ~lmm* Outer

Transverse and longitudinal stresses in header N/A

Longitudinal stresses in weld (Line 2)

Longitudinal stresses in weld (Line 5)

Transverse stresses in stub (Lines I and 4)

-50

-53

-69

N/A

43

67

90

Membrane

-4

7

II

Bending

-47

-60

-80

Inner

-

.............................@ USING FKACI'UKE MECIIANICS 1'0CLAIM EXEMPTION FROM PWHT- FOUR CASE STUDIES

Tnble 4 Scope of fracture assessments and dimensions of flaws considered in Case B

Location

Orientation

Height

Length

Ligament

Ref.

12mm 12mm 12mm

215mm(') 215mm ( I ) 2 15mm ( I )

3.0mm 1.5mm N/A

s12hIe3a sl2hlela sl2hlsna

Header Header Header

Longitudinal Longitudinal Longitudinal

Type Embedded Embedded Surface (3'

Weld Weld Weld

Transverse Transverse Transverse

Embedded Embedded Embedded

12mm 12mm 12mm

12mm 12mm 12mm

l .Omm l .Omm 1.Omm

sl2wtela sl2wtel b sl2wtelc

Stub Stub

Longitudinal Longitudinal

Embedded Surface

8.0mm 5.3mm

152mm (2) 152mm (2)

I .Omm N/A

sO8sle l b s06slsnb

Note: ( I ) Length of weld toe circuniference on header (2) Length of weld toe circumference on stub (3) Flaw breaking on outer surface

Case A: Avoidance of PWHT of a propane rherlcal m e 1

Operacing cmdlUon

Sf Ver. 2.066 -0.98062

Fig. 1 Case A. Assessment of as-welded vessel (operating condition, 32°C)

Case A: Avoidance of PWHT of a propane spherical vessel Prooftest condiUon

Sr Ver. 2.066 -0.98062

Fig. 2 Case A. Assessment of as-welded vessel (proof test condition, 10°C)

Case A: Avoidance of PWHZ of a pmpane spherical vessel Deslgn CondMon

Sr

Ver. 2.056

- 0.98052

Fig.3 Case A. Assessment of as-welded vessel (design condition, -46OC)

Flaw iii

Fig. 4 Case B: Locations of stress distributions from finite element analysis

Case Study C7: Avoidance of PWH't for a Ti riser

Sr

-

Ver. 2.056 0.98052

Fig.5. Case C: As-welded Ti riser

Case Study C3: Avoidance of PWHT for a Ti riser Required fracture toughness 2.07

2

1.0-

0

0

1

-

Ver. 2.056

-

-

- 0.98052

-

-

-

-

1 .o

.

-

-

-

-

-

Sr

Fig.6. Case C: Effect of assumed fracture toughness value, Ll

-

2.0

-

I

Case Study C2: Avoldance of PWHTfora Tiriser Tolerable rssidual stresses

Sr

-

Ver. 2.056 0.98052

Fig.7. Case C: Effect of assumed secondary membrane stress

Case D: Avoidance of PWHT of a HPHTsepraIor

Var. 2.066

-

Sr 0.97103

Fig. 8 Case D: Level 2 assessment of girth welds

. sr

Ver. 2.056

- 0.97103

Fig.9. Case D: Level 2 assessment of longitudinal seam welds

APPENDIX A Output from Crackwise 2 for Case A

-

-

Crackwise Version 2.056 0.98052 Wednesday, Apr 07,1999

INPUT File: H:\7308\KG\CVKI -1.CW2

Project ID Case A: Avoidance of PWHT of a propane sherical vessel 730813 A Muhammed

Project title: Project number: Name: Date: Comments:

Operating condition Draft 887910 Annex K (1998) CV-Kcorrelations used in analysis

Calculation type Assessment level: Anatysis type:

1 Known parameter analysis

Geometry, mrn Flaw type: Flaw depth, a: Section thickness, 8: Parametric angle: Bulging correction factor applied

Surface flaw 2.000 35.200

Flaw length, 2c: Section width, W:

Max Radius of curvature, R:

7000.000

Section thickness, 61: Exponent, n:

35.200 1.500

Misalignment Butt weld, axial, vessel seam Misalignment, e: Section thickness, 82: Misalignment factor:

Total misalignment factor, Pb'lPm:

Stresses, MPa Primary membrane stress, Pm: Primary bending stress, Pb:

SCFrn: SCFb:

Weld condition: As welded Appropriate yield strength, sy*: Thermal membrane stress, Qtm:

Thermal bending stress, Qtb:

Proof test conditions Yield strength, sy*: Membrane stress, Pm*:

Tensile strength, su": Bending stress, Pb*:

Tensile properties, MPa Failure locus type - Level 1 Yield strength, sy: Young's modulus, E:

Tensile sbengtfr, su:

Toughness (K), NlmrnA3/2 Toughness:

OUTPUT Known parameter calculation Assessment result

Acceptable

FAD coordinates Kr:

Sr Parametric angle:

90.000 deg.

Secondary stresses Qrn:

225.673

Messages:

Qb:

Calculation has WARNINGS :Back check (negathre FAD slope), due to Strength,

9.610

-

TW

-

Crackwise Version 2.056 0.98052 Wednesday. Apr 07, 1999

INPUT File: H:\7308\KG\CVKl-2.CW2

Project ID Project We: Project number: Name: Date: Comments:

Case A: Avoidance of WVHT of a propane spherical vessel 730813 A Muhammed Proof test condition Oraft BS 7910 Annex K (1998) CVKcorrelations used in analysis

Calculation type Assessment level: Analysis type:


Geometry, mm Flaw type: Flaw depth, a: Section thickness, B: Parametric angle: Bulging correction factor applied

Surface flaw 2.000 35.200 Max

Flaw length, 2c: Section width, W: Radius of curvature, R:

7000.000

Section thickness, B1: Exponent, n:

35.200 1.500

Misalignment Butt weld, axial, vessel seam Misalignment, e: Section thickness, 82: Misalignment factor: Total misalignment factor, Pb'lPm:


SCFm: SCFb:

Weld condition: As welded Appropriate yield strength, sy': Thermal membrane stress, Qtm:


Tensile properties, MPa Failure locus type - Level 1 Yield strength, sy: Young's modulus, E:

Tensile strength, su:

Toughness (K), N/mmA3/2 Toughness:

OUTPUT Known parameter calculation Assessment result:

Acceptable

FAD coordinates Kr: Sr: Parametric angle:

90.000 deg.

Seconda~ystresses Qm:

344.740

Messages:

Qb:

Calculation has WARNINGS : Back check (negative FAD slope), due to Strength,

0.000

-

-

Crackwise Version 2.056 0.98052 Wednesday, Apr 07, 1999

INPUT File: H:\7308\KG\CVKl-3.CW2


Case A: Avoidance of PWHT of a propane spherical vessel 730813 A Muhammed Design condition Draft BS 7910 Annex K (1998) CV-K correlations used in analysis min. design ternerature of -48 deg. C

Calculation type Assessment level: Analysls type:


Geometry, mm Flaw type: Flaw depth, a: Section thickness, 8: Parametric angle: Bulging correction factor applied



Misalignment Butt weld, d a l , vessel seam Section thickness, B1: Exponent, n:

Misatignment, e: Section thickness, 62: Misalignmentfactor: Total misalignment factor, Pb'lPm:


SCFm: SCFb:

Weld condition: As welded Appropriate yield strength, sy': Thermal membrane stress, Qtm:


Proof test conditions Yield eength, sy': Membrane stress, Pm":

131.400

Tensile strength, sue: Bending stress, Pb':

Tensile properties, MPa

-

Falure lacus type Level 1 Yield sbength, sy: Young's modulus, E:

f ensile strength, su:

Toughness (K), N/mmA3/2 Toughness:


Acceptable

FAD coordinates Kr: Sr:

Parame& angle:

90.000 deg.

Secondary stresses Qm:

225.673

Messages:

Qb:

Calculation has WARNINGS : Back c h e c k (negative FAD slope), due to Strength,

482.630


0 0

APPENDIX B

a

a

Output from Crackwise 2 for Case B

'

-

-Version 2.056 0.972101

TFQT ---d

Wednesday, Oct 22, 1997

INPUT File: G:\MJC\CRP-7308\S12HLE3A.CW2

Project ID PWHT case studies; Case 0 7038 M J Cheaitani

Project We: Project number: Name: Date: Comments:

Servive temp; 2a=12; in Header, Longitudinal, Embedded, p=3; a; File s12hle3a

Calculation type 2 Known parameter analysis

Assessment level: Analysis type:

Geometry, mm Embedded flaw 12.000 52.000 3.000

Flaw type: Flaw depth, 2a: Section thickness, B: tigament height, p: Flaw at weld toe

Flaw length, 2c: Section width, W: Attachment length, L:

Stresses, MPa Primary membrane stress. Pm: Primary bending stress, Pb:

Weld condition: As welded - residual stress relaxation enabled Appropriate yield strength, sy': 275.000 Thermal membrane stress, Qtm: 0.000


Tensile properties, MPa Failure locus type - Low work hardening materials Tensile strength, su:

Yield strength,sy: Young's modulus, E: Resolution (increments)

Toughness (K), MPa.mA0.5 Toughness:

OUTPUT Known parameter calculation Assessment resuft

Acceptable


Secondary stresses

Qm: Messages:

275.000

Qb:

Calculation has WARNINGS : Back check (negative FAD slope), due to Strength.

0.000

r

Crackwise -Version 2.056

Wednesday, Oct 22,1997

",y\.\,\,, * ' -__- A I I / / / .<,

-?.re

- 0.972101

\;I\,

1

.-L'L

INPUT File: G:\MJC\CRP-7308\S12HLEIACW2


PWHT case studies: Case B 7038 M J Cheaitani Sewice temp; 2a=12; in Header. Longitudinal. Embedded, p=1.5: a; File s12hlela



Geometry, mm Flaw type: Flaw depth, 2a: Section thickness. 8: Ligament height, p: Flaw at weld toe

Embedded flaw 12.000 52.000 1.500

Flaw length. 2c: Section width. W:

214.600 430.000

Attachment length. L:

20.000

Stresses, MPa Primary membrane stress. Pm: Primary bending stress. Pb:

SCFm: SCFb:

Weld condition: As welded -residual stress relaxation enabled Appropriate yield strength, sy': 275.000 Thermal membrane stress. Qtrn: 0.000

Thermal bending stress. Qtb:

0000


209.000


-

Failure locus type Low work hardening materials Yield sb-ength, sy: Young's modulus. E:

174.000 1.70E+05

Resolution (increments)

100.000



Acceptable

FAD coordinates

Kr: Sr: Secondary stresses Qm: Messages:

275.000

Qb:

Calculation has WARNINGS : Back check (negative FAD slope), due to Strength.

L~kwise '

-Version 2.056

Wednesday, Oct 22, 1997

- 0.972101

I

II

L-~V

\.T

_--.-

i .,'

I;?

/!

d;

,I.-_-

File: G:\MJC\CRP-7308\S12HLSNA.CW2

Project ID PWHT case studies; 7038 M J Cheaitani

Case B

Service temp; a=12; in Header, Longitudinal, Surface. p=n; a; File sl2hlsna



Geometry, mm Surface flaw 12.000 52.000 Normal

Flaw type: Flaw depth, a: Section thickness, B: Bending restraint: Flaw at weld toe

Flaw length, 2c: Section width, W: Parametric angle: Attachment length, L:

214.600 430.000 Max 20.000


0.000

Stresses, MPa Primary membrane stress, Pm: Primary bending stress, Pb: Weld condition: As welded - residual stress relaxation enabled 275.000 Appropriate yield strength, sy': Thermal membrane stress, Qtm: 0.000


-

Failure locus type Low work hardening materials Yield strength, sy: Young's modulus, E:

174.000 1.70E+05


100,000




Acceptable

FAD coordinates Kr:

Sr: ParameMc angle:

90.000 deg.


275.000

Messages:

Qb:


.;

.:' /

INPUT

Project We: Project numbec Name: Date: Comments:

I

1 1 \;yl-

:

r

-

Crackwise Version 2.056

Tuesday, Nov 25, 1997

- 0.97103

INPUT File: G:\MJC\CRP-730B\S12WTE 1A.CW2



Service temp; 2a=12; in Weld, Transverse. Embedded, p=l; a; File sl2wtela Parent metal tensile properties are used, Sbesses on Line 2, NOthermal stresses



Geometry, mm Embedded flaw 12.000 14.000 1.000

Flaw type: Flaw depth, 2a: Section thickness, B: Ligament height, p:



SCFm: SCFb:

Weld condition: As welded - residual stress relaxation enabled Appropriate yield strength, sy*: 370.000 Thermal membrane stress, Qtm: 0.000


0.000

Tensile properties, MPa Failure locus type Low work hardening materials

-

Yield strength, sy. Young's modulus, E:

174.000 1.70€+05


100.000


Toughness (K), MPa.mA0.5 Toughness.

OUTPUT Known parameter calculation Assessment resutt:

Acceptable

FAD coordinates Kr: S r: Secondary stresses Qm: Messages:

336.420

Qb:

0.000

Cafculatlon has WARNINGS :Mk: d2c > 0.5, Back check (negative FAD slope), due to Flaw depth, due to Primary membrane stress, due to Prlmary bendlng stress, due to Strength, due to Constant aspect ratlo, due to Constant prlmary stress ratlo,

PWHT case studies; Case B Sewice temp; 2a=12; in Weld, Transverse, Embedded, p-1; a; File s l t w t e l a

Sr

-

Ver. 2.056 0.97103

- Version 2.056 - 0.97103


INPUT File: G:\MJC\CRP-7308\S12VVTElB.CWZ

Project ID PWHT case studies; Case 0 7038 M I. Cheaitani

Project We: Project number: Name: Date: Comments

Service temp; 2a=12; in Weld, Transverse. Embedded, p=l; b; File sl2wtelb Parent metal tensile properties are used, SVesses on Line 5, No thermal stresses

Calculation type 2


Known parameter anaiysis

Geometry, mm Embedded Raw 12.000 14.000

Flaw type: Flaw depth. 2a: Section thickness, B: Ligament height, p:


1.ooo

Stresses, MPa Primary membrane sbess, Pm: Primary bending skess, Pb:

SCFm: SCFb:

Weld condition: As welded - residual stress relaxation enabled Appropriate yield strength, sy': 370.000 Thermal membrane stress, Qtm: 0.000


0.000

Tensile properties, MPa Failure locus type - Low work hardening materials Yield strength, sy: Young's modulus, E:





Acceptable

FAD coordinates Kr: Sr: Secondary stresses Qm: Messages:

330.990

Qb:

0.000

Calcufationhas WARNINGS :Back check (negative FAD slope), due to Flaw depth, due to Primary membrane stress, due to Strength,

PWHT case studies; Case

B

Service temp; 2a=12; in Weld, Transverse, Embedded, p=l; b; File sl2wtelb

Sr

Ver. 2.056

- 0.97103

r

Crackwise -Version 2.056

I

- 0.97103

I

Tuesday. Nov 25, 1997

Ttpa

INPUT File: G:\MJC\CRP-7308\S12WTE1CCCW2

Project ID Project Me: Project number. Name: Date: Commenh:

Senrice temp; 2a=12; in Weld. Transverse. Embedded, p=l; c; File slZwtelc Parent metal tensile properties are used. Stresses on Line 3, No thermal stresses

Calculation tvoe 2 Known parameter analrjis

Analysis type:

Geometry, mm Flaw type: Flaw depth. 2a: Sedan thickness, 8: Ligament height, p:

Embedded Raw 12.000 14.000 1.000

Flaw length. 2c: Section width, W:

Stresses, MPa Primary membrane stress. Pm: Primary bending stress, Pb:

SCFm: SCFb:

Weld condition: As welded -residual stress relaxation enabled Appropriate yield strength, sy': 370.000 0.000 Thermal membrane stress. Qtrn:

Thermal bending stress. Qtb:

0.000


209.000


174.000 1.70E+05


100.000


100.000

OUTPUT K n o w parameter calculation Assessment resun:

Acceptable

FAD coordinates Kr: Sr: Secondary stresses Qm: Messaaes:

Calculatlon has WARNINGS : Mk: a12c > 0.5. Back check (neaatlve FAD s l o ~ e l .due to Flaw d e ~ t h .due to Flaw length, due to Primary membrane stress, due to ~ ; f m i r ybending s&ess, due to ~treng'th,d u e to Constant aspect ratlo, due to Constant prlmary stress ratlo,

a PWHT case studies; Case

•

Service temp; 2a=12; in Weld, Transverse, Embedded, p=l; c; File s l l w t e l c

a a a a

0

B

Ver. 2.056

- 0.97103

- Version 2.056 - 0.971 0 3

Tuesday. Nov 25, 1997

INPUT File: G:\MJC\CRP-7308\SO8SLEl A.CW2


Project We: Project number. Name: Date: Comments:

Service temp; 2a=8; in Stub, Longitudinal, Embedded, p = l ; a; File s08slela



Geometry, mm Embedded flaw 8.000 10.000 1.ooo

Flaw type: Flaw depth, 2a: Section thickness, B: Ligament height, p: Flaw at weld toe


Stresses, MPa Primary membrane stress, Prn: Primary bending stress, Pb:

SCFm: SCFb:

Weld condition: As welded - residual stress relaxation enabled 275.000 Appropriate yield strength, sy': Thermal membrane stress, Qtm: 0.000

Thermal bending stress, ~ t b :


-


174.000 1.70E+05


100.000




Acceptable

FAD coordinates Kr: Sr: Secondary stresses

Qm: Messages:

275.000

Qb:

Calculation has WARNINGS :Back check (negative FAD slope), due t o Strength,

a

a a


B

Service temp; 2a=8; in Stub, Longitudinal. Embedded, p=l; a; File sO8slela

a a a

2.0-

a a a a

2

I.O-

0

a a a a

a a

0, 0

Sr

a

• a a a a a

a a 0

a a

a a a a

I .o

-

Ver. 2.056 0.97103

1

2.0

- Version 2.056 - 0.971 03


INPUT File: G:\MJC\CRP-7308\S08SLEI B.CW2



Service temp; 2a=8; in Stwb, Longitudinal. Embedded, p=l; b; File s08slelb



Geometry, mm Embedded Raw

Flaw type: Flaw depth, 2a: Section thickness, 6: Ligament height, p: Flaw at weld toe

8.000

10.000 1.OOO


Stresses, MPa Primary membrane stress, Pm: Primary bending stress, Pb: Weld condition: As welded - residual stress relaxation enabled 275.000 Appropriate yield strength, sy': Thermal membrane stress, Qtm: 0.000


Tensile properties, MPa ~ailurelocus type - Low work hardening materials Yield strength, sy: Young's modulus, E:

174.000 f.70E+05


100.000


Toughness (K), MPa.rnAO.S Toughness:


Acceptable


Secondary stresses Q m: Messages:

275.000

Qb:


PWHT case studies; Case B SeWlce temp; Za=8; in Stub, Longitudinal, Embedded, p a l ; b; File s08slelb

Sr

Ver. 2.056 - 0.97103

r

-

Crackwise Version 2.056


- 0.97103

j

=-*1 \$,?[

jI

nz.--,,., 4 U

_

;.,

INPUT File: G:\MJC\CRP-7308\S06SLSNA.CW2

Project ID PWHT case studies; Case B 7038 M J Cheaitani


Service temp; a=6; in Stub, Long'hdinal, Surface, p=n; a; File sO6slsna Flaw tength = full circumference of stub

Calculation type Assessment level: Analysis type: Critical parameter:

Z

Critical parameter analysis Ftaw depth

tolerance:


Flaw type: Flaw depth, a: Section thickness, 8: Bending restraint: Flaw at weld toe

Stresses, MPa

Flaw length, 2c: Section width,W: Parametric angle: Attachment length, L:

Primary membrane stress, Pm: Primary bending stress, Pb:

SCFm: SCFb:

Weld condition: As welded - residual stress relaxation enabled Appropriate yield strength, sy*: 275.000 0.000 Thermal membrane stress, Qtm:


Tensile properties, MPa Failure locus type Low work hardening materials

-

Yield strength, sy: Young's modulus, E:

174.000 1.70E+05

Resolubon (increments)

100,000


Toughness (K), MPa.mAO.S Toughness:

Other data Solver control setbngs: Initial guess: Max. step size:

Initial step sire: Max. no. iterations:

OUTPUT Cribcal parameter calculation Assessment result:

Crrtical

Critical parameter Ivalue:

Flaw depth

5.433

FAD coordinates Kr: Sr: Parametric angle:

90.000 deg.

Secondary stresses Qm: Messages:

Calcutatton has WARNINGS : Back check (negatrve FAD slope), due to Strength,

151.700 304.000 Max 62.000

0.000

_

Y

!

a a a a a a a a a

PWHT case studies; Case B Service temp; a=6; in Stub, Longitudinal, Surface, p=n; a; File sO6slsna

a a a

a • a a a a a a a a a a a a a

-

Ver. 2.056 0.97103

-

-

Crackwise Version 2.056 0.971 03 Tuesday, Nov 25, 1997

INPUT File: G:\MJC\CRP-7308\S06SLSNBBCW2

Project ID Project We: Project number: Name: Oate: Comments:

PWHT case studies; Case B 7038 M J Cheaitani Service temp; a=6; in Stub, Longitudinal. Surface, p=n; b; File sO6slsnb Flaw length = full circumference of stub

Calculation type Assessment level: Analysis type: Critical parameter:

2 Critical parameter analysis Flaw depth

tolerance:

Geometry, mm Flaw type: Flaw depth, a: Section thickness, B: Bending reskaint: Flaw at wefd toe

Surface flaw 6.000 10.000 Normal

Flaw length, 2c: Section width, W: Parametric angle: Attachment length, L:

151.700 304.000 Max 62.000

Stresses, MPa Primary membrane stress, Pm: Primary bending sbess, Pb:

SCFrn: SCFb:

-

Weld condition: As welded residual stress relaxation enabled Appropriate yield strength, sy*: 275.000 Thermal membrane stress, Qtm: 0.000


0.000

Tensife strength, su:

209.000


-


174.000 1.70E+05


100.000

Toughness (K), MPa.mAO.S Toughness:

Other data Solver control settings: Initial guess: Max. step sue:

Initial step size: Max. no. iterations:

OUTPUT Critical parameter calculation Assessment result:

Critical

Critical parameter Ivatue:

Flaw depth


Parametric angle:

90.000 deg.

Secondary stresses

Qrn: Messages:

275.000

Qb:

Calculatlon has WARNINGS : Back check (negative FAD slope), due to Strength,


B

Service temp; anb; in Stub, Longitudinal, Surface, p=n; b; File s06slsnb

Ver. 2.056

APPENDIX C Output from Crackwise 2 for Case C

-

-

Crackwise Version 2.056 0.98052 Wednesdav. Dec 02. 1998

INPUT File: H:\CSW\CRP98-00\7308CIA.CW2

Project ID Case Studv C1: Avoidance of PWHT for a Ti riser 7308 C S Wiesner see above Tolerable residual stresses

Proiect title: Proiect number: Name: Date: Comments:

Calculation type 2 Known ~arameteranalvsis

Assessment level: Analvsis tvDe:


Ftaw tvDe: Ftaw death. a: Section thickness. B: Bendina restraint: Kastner colla~sesolution

Flaw lenath, 2c: Section width. W: Parametric anale: Radius of curvature. R:

12.700 678.000 Max 108.000

Stresses, MPa Primarv membrane stress. Pm: Primarv bendina stress, Pb:

SCFrn: SCFb:

Weld condition: Known - residual stress relaxation enabled Secondarv membrane stress. Qm: 620.000 A~arooriatevietd strenath, sv*: 758.000 Thermal membrane stress. Qtrn: 0,000

Secondan, bendina stress. Qb:

0.000

Thermal bendina stress. Qtb:

0.000

Tensile slrenath, su:

824.000

Qb:

0.000

Tensile properties, MPa Failure locus type - Low work hardening materials Yield strenath, sv: Youna's modulus. E:

758.000 1.1OE+05


100.000

Toughness (K), NlmmA312 Touahness:

OUTPUT Known oarameter calculation Assessment result:

Not Aueotable

FA0 coordinates Kr: Sr: Parametric anale: Sewndarv stresses

Om: Messages:

493.096

Calculation has WARNINGS : Back check (negative FAD slope), due to Primary membrane stress, due to Primarv bendina stress. due to Strenath. due to Constant arimarv stress ratio.

-

-

Crackwise Version 2.056 0.98052 Wednesdav. Dec 02. 1998

INPUT File: H:\CSW\CRP98-00\7308C3A.CW2

Project ID Proiect title: Proiecl number: Name: Date: Comments:

Case Studv C3: Avoidance of PWHT for a Ti riser 7308 C S Wiesner see above Reauired fracture touahness

Calculation type Assessment level: Analvsis tvoe: Critical Darameter:

2 Critical oarameter analvsis Touahness

tolerance:

Geometry, mm Flaw tvoe: Flaw deoth, a: Section thickness. B: Bendina restraint: Kastner collawse solution

Surface flaw 1.500 28.130

Normal

Flaw length. 2c: Section width. W: Parametric anale: Radius of curvature. R:

12.700 678.000

Max 108.000

Stresses, MPa Primarv membrane stress. Pm: Primarv bendina stress. Pb:

SCFm: SCFb:

Weld condition: Known - residual stress relaxation enabled Secondarv membrane stress. Qm: 620.000 Aoarooriate vield strenath. sv': 758.000 0.000 Thermal membrane stress. Qtm:

Secondarv bendina stress. Qb:

0.000

Thermal bendina stress. Qtb:

0.000

Tensile strenath. su:

824.000

Tensile properties, MPa Failure locus type - Low work hardening materials Yield strenath. sv: Youna's modulus. E:

758.000 1.10E+05


100.000

Toughness (K), NlmmA3/2 Touahness:

Other data Solver control settinas: Initial auess: Max. steo size:

Initial steo size: Max. no. iterations:

OUTPUT Critical ~arametercalculation Assessment result:

Critical

Critical ~arameterIvalue:

f ouohness

3144.375

FAD coordinates Kr: Sr: Parametric anale:

90.000 dea.

Secondarv stresses Qrn:

493.096

Messages:

Qb:

0.000

Calculation has WARNINGS : Back check (negative FAD slope), due to Primary membrane stress, due to Primarv bendina stress. due to Strenath. due to Constant ~ r i m a r vstress ratio.

-

-

Crackwise Version 2.056 0.98052 Wednesdav. Dec 02.f 998

INPUT File: H:\CSW\CRP98-00\7308C2.CW2

Project ID Case Studv C2:Avoidance of PWHT for a Ti riser

Proiect title: Proiect number: Name: Date: Comments:

7308 C S Wiesner see above Tolerable residual stresses

Calculation type 2 Critical oarameter analvsis Secondarv membrane stress tolerance:

Assessment level: Analvsis tvoe: Critical oarameter:

Geometry, mm Flaw tvoe: Flaw d e ~ t h a: . Section thickness. 8 : Bending restraint: Kastner collaose solution

Surface flaw

1.500 28.130 Normal

Flaw lenath. 2c: Section width. W: Parametric anale: Radius of curvature. R:

12.700 678.000 Max

108.000

Stresses, MPa Primarv membrane stress. Pm: Primarv bendina stress. Pb:

SCFm: SCFb:

Weld condition: Known - residual stress relaxation not enabled 620.000 Secondaw membrane stress. Qm: Thermal membrane stress. Qtm: 0.000

Secondarv bending stress. Qb: Thermal bendina stress. Qtb:

0.000 0.000

Tensile strength. su:

824.000

Tensile properties, MPa Failure locus type - Low work hardening materials Yield strenath. sv: Youno's modulus. E:

758.000 1.1 0E+05


100.000

Toughness (K), NlmmA312 Touahness:

Other data Solver control settings: Initial guess: Max. steo size:

Initial steD size: Max. no. iterations:

OUTPUT Critical oarameter calculation Assessment resu[t:

Critical

Critical oarameter Ivalue:

Secondaw membrane stress 207.250

FAD coordinates Kr: St: Parametric anate: Secondaw stresses Qm: Messaoes:

207.250 Calculation successfullv cornoleted.

Qb:

a

USING FRACTURE MECHANICS T o CLAIM EXEMPTION FROM PWHT- FOUR CASE STUDIES

0

APPENDIX D Output from Crackwise 2 for Case D

a

a

a

a

-

1

-

Crackwise Version 2.056 0.98052

woo

Wednesday, Apr 07, 1999

a

• a a

•

INPUT File: H:\7308\GIRTH.CW2

Project ID Project title: Project number: Name: Date: Comments:

Case D: Avoidance of PWHT of a HPHT separator 730813 A Muharnmed Circumferential (GIRTH) weld

Calculation type 2 Known parameter anatpis

Assessment level:

Analysis type:

Geometry, mm Flaw type: Flaw depth, a: Seetion thickness, 6: Bending restraint:

Surface flaw 2.000 34.290 Normal

Flaw length, 2c: Section width, W: Parametric angle:

8.000 5745.300 Max

Misalignment Butt weld, axial, vessel seam Misalignment, e: Section thickness, 82: Misalignment factor:


Total misalignment factor, Pb'IPm:

Stresses, MPa Primary membrane stress, Prn: Primary bending stress, Pb:

0

@

a

48.670 0.000

Weld condition: As welded - residual stress relaxation enabled Appropriate yield strength, sy': 262.200 Thermal membrane stress, Qtm: 0.000 Proof test conditions Yield strength, sy': Membrane stress, Pm?

SCFm: SCFb:

Thermal bending sbess, Qtb: Tensile strength, sue: Bending stress, Pb':


262.200 2.07E+05


100.000


Toughness (K), NlmmA3/2 Toughness:

2433.900

OUTPUT Known parameter calculation

a a

0.000

Asressrnent resuk

Acceptable

FAD coordinates Kr: Sr: Paramebic angle:

90.000 deg.

Secondary e e s s e s Qm:

262.200

Messages:

Qb:

Calcuhtlon has WARNlNGS :Back check (negatfve FAD Slope), due to Strength,

483.000

-

-

Crackwise Version 2.056 0.98052 Wednesday, Apr 07, 1999

INPUT File: H:\7308\LONG.CW2

Project ID Case 0:Avoidance of PWHT of a HPHT separator 730813 A Muhammed

Project We: Project number: Name: Date: Comments:

Longitudinal seam weld



Geometry, rnm Flaw type: Flaw depth, a: Section thickness, B: Parametric angle: Bulging correction factor applied



Misalignment Butt weld, axial, vessel seam Misalignment, e: Section thickness, 62: Misatignment factor:


Total misalignment factor, Pb'lPm:

Stresses, MPa Primary membrane stress, Pm: Primary bending stress, Pb: Weld condition: As welded - residual stress relaxation enabled Appropriate yield strength, sy*: 262.200 Thermal membrane stress, Qtm: 0.000 Proof test conditions Yield strength, sy': Membrane stress, Pm':

Thermal bending stress, Qtb: Tensile strength, su': Bending stress, Pb*:


262.200 2.07€+05


100.000


Toughness (K), NlmmA312 Toughness:

OUTPUT K n o w parameter calculation Assessment result:

Acceptable


Paramebic angle:

90.000 deg.


228.368

Messages:

Qb:

Calculation has WARNINGS : Back check (negatlve FAD slope), due to Strength,

0.000

Quality Assessment of TWI1s Core Research Programme As part of the TWI continuous improvement scheme, we are seeking to establish views on the quality of individual reports produced from the Core Research Programme (CRF). If you would like to contribute to the assessment of this report, I would be grateful if you could complete the short questionnaire given below, and return this proforma to me, within one month.

Richard Dolby Director, Research & Technology

Report Title: Report Number: Author(s): (Please rick appropriate boxes)

(related to objectives)

Other comments:

Please note that reports given marks in the 'poor' category will be subject to a

TWIformal complaint procedure High My competence in the subject area is:

Medium

I

Reviewer: (please print clearly) Name: ........................................................................................................................................................................ Company: ................................................................................................................................................................... Date: ........................................... Thank you. Please return to Director of Research & Technology, ?1M, Granta Park, Great Abington, Cambridge CBI 6AL, UK or fax directly to +44 (0)1223 8901 10

,

. . . . . . .:.

.

TU71, Ahingron Hall,:\bingcon.. , . . .~. Cambridge CBi bAL United Kingdom ', , .

.<

.

Resirtckcd No.JOSSSS Faglan? ,: ,. TWI is the husincr? nrmc of. , ' The Welding hsiimte - ,

. .

.

.

. .

'

. .

.

.

"

. .

.

..

. . .. .. .. .

~

. . .

. . . . . .. .. . .. .. . - . ..:: .

'

'

.

.

.:

.I

~

,

,

' ':,

,

,

~~

.

.. . .

~~.

. .. . . . . . : ;

. ~

:..

PWHT Exemption

Recommend Documents