1、Technical Report on Material ToughnessAPI 6AMSECOND EDITION, SEPTEMBER 1, 1995(FORMERLY BULLETIN 6AM)American Petroleum Institute1220 L Street, NorthwestWashington, D.C. 20005Technical Report on Material ToughnessExploration and Production DepartmentAPI 6AMSECOND EDITION, SEPTEMBER 1, 1995(FORMERLY
2、BULLETIN 6AM)AmericanPetroleumInstituteSPECIAL NOTESAPI publications necessarily address problems of a general nature. With respect to par-ticular circumstances, local, state, and federal laws and regulations should be reviewed.API is not undertaking to meet the duties of employers, manufacturers, o
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10、 the accuracy and reliability of the data contained in them;however, the Institute makes no representation, warranty, or guarantee in connection withthis publication and hereby expressly disclaims any liability or responsibility for loss ordamage resulting from its use or for the violation of any fe
11、deral, state, or municipal regu-lation with which this publication may conflict.API technical reports are published to facilitate the broad availability of the informa-tion contained therein. These documents are not intended to obviate the need for applyingsound engineering judgment regarding when a
12、nd where this information should be utilized.The formulation and publication of API technical reports is not intended in any way to in-hibit anyone from using any other data, information, or practices.Copyright 1995 American Petroleum InstituteiiiCONTENTSPage1 SCOPE . . . . . . . . . . . . . . . . .
13、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Initial Task Group Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Amended Task Group Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 GENERAL HISTOR
14、Y OF API 6A/6D ACTIVITIES RELATIVE TO IMPACT TESTING OF MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 MATERIALS TOUGHNESS TASK GROUP HISTORY . . . . . . . . . . . . . . . . . 24 API SPECIFICATION 6A, FIFTEENTH EDITIONBRITTLE FRACTUREPREVENTION BENEFITS . . . . . . . . .
15、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.2 Design Considerations Now Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.3 Design Methods Now R
16、equired . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.4 Materials Requirements Now Included . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.5 Comprehensive Welding Requirements Have Been Established . . . . . . . . 34.6 Important New Quality Control Requirements Hav
17、e Been Added . . . . . . . 35 ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35.1 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35.2 The Use of CVN Requirements in Mater
18、ials Specifications . . . . . . . . . . . 35.2.1 Historical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35.2.2 Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.2.3 Fitness-For-Purpose Analyses . . . . . . . . . . . .
19、. . . . . . . . . . . . . . . . . 45.3 API 6A Task Group FitnessFor Purpose Analysis . . . . . . . . . . . . . . . . . 45.3.1 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.3.2 Design Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20、 . . . . . . . . . . . . . 45.3.3 Defect Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.3.4 KIC-CVN Correlations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55.3.5 Derivation of the CVN Toughness Requirement . . . . . . . . . .
21、 . . . . . 55.3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55.3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6APPENDIX AREFERENCES AND BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . 1
22、1Figures1CVN Values for 75K MaterialSurface Crack and 50 ksi Stress . . . . . . . . . 72CVN Values for 75K MaterialSurface Crack and 75 ksi Stress . . . . . . . . . 83CVN Values for 75K MaterialVolumetric Crack and 50 ksi Stress . . . . . . 94CVN Values for 75K MaterialVolumetric Crack and 75 ksi St
23、ress . . . . . . 10Tables1CVN Values Derived by KIC-CVN Correlations . . . . . . . . . . . . . . . . . . . . . . 5vFOREWORDThis technical report is under the jurisdiction of the API Subcommittee on Valves andWellhead Equipment. It is a report of the methodology and conclusions of a task groupstudy o
24、f material toughness requirements for equipment covered by API Specification 6A,Specification for Wellhead and Christmas Tree Equipment. The report was first issued asAPI Bulletin 6AM, First Edition, September 1, 1989, and was reaffirmed and reissued in1995 as a technical report designated API 6 AM.
25、This document was produced solely for the purpose of disseminating technical infor-mation and is not an API standard. API publications may be used by anyone desiring to doso. Every effort has been made by the Institute to assure the accuracy and reliability of thedata contained in them; however, the
26、 Institute makes no representation, warranty or guar-antee in connection with this publication and hereby expressly disclaims any liability orresponsibility for loss or damage resulting from its use or for the violation of any federal,state, or municipal regulation with which this publication may co
27、nflict.Suggested revisions are invited and should be addressed to the director of the Explo-ration and Production Department, American Petroleum Institute, 1220 L Street, N.W.,Washing ton, D.C. 20005.This publication shall become effective on the date printed on the cover but may be usedvoluntarily
28、from the date of distribution.SUMMARYCVN toughness requirements can be used as a quality assurance measure in API Speci-fication 6A equipment to screen materials with poor notch toughness. This should help tominimize brittle fracture of wellhead and of christmas tree equipment in the field.A minimum
29、 average of 15 ft-lb is justified in API Specification 6A for all temperatureclassifications of all PSL levels of equipment. This does not preclude the use of the currentlateral expansion requirements for PSL level 4 equipment. The Task Group recommends20 ft-lb. This compromise required that the Tas
30、k Group stipulate 15 ft-lb in the transversedirection: in order to satisfy logic that required 15 ft-lb in the transverse direction, a lon-gitudinal equivalent was necessary.Additional work is required to establish brittle fracture criterion for API Specification6A materials using Charpy-fracture me
31、chanics correlations.11 Scope1.1 INITIAL TASK GROUP CHARGEThe July 30, 1986, API Subcommittee Meeting Minutescontained the Material Toughness Task Group Charge. Itcomprised Attachment 6. The charge(s) were:1. Evaluate the material toughness requirements for APISpecification 6A materials, for accepta
32、nce worldwide.2. Perform a survey of the industry and review literature formaterial toughness values based on technical data and designrequirements.3. Devise a method or action to resolve difference betweenthe European and U.S. opinions on material toughness.4. Establish work groups to prepare appro
33、priate revisionsto API Specification 6A for ballot by June 1987.1.2 AMENDED TASK GROUP CHARGEThe Task Group came to several conclusions based on thecharges:Charge 1: The Task Group could not evaluate worldwideparameters necessary for acceptance of API Specification6A materials toughness requirements
34、. The justification forother groups requirements was not readily obvious.Charge 2: The members of the Task Group comprised across section of industry users and manufacturers whichhave worldwide exposure. The Task Group could not docu-ment any materials related failures on equipment whosematerials ha
35、d met the API Specification 6A requirement of15 ft-lb. All documentable failures did not meet the exist-ing requirements. A literature survey revealed no technicaldata or design requirements which are relatable to APISpecification 6A equipment design or usage.Charge 3: The differences between U.S. a
36、nd Europeanopinions on material toughness relate directly to a differ-ence in philosophy. There are several differences, but themajor difference is that the Europeans feel that the Charpyvalue relates to design while the U.S. opinion is that theCharpy test is a quality assurance exercise in sorting
37、outrogue materials. All other differences stem from that ma-jor premise.Unfortunately, the technical justification of either of therequirements is unclear. The historical evidence indicatesthat both approaches are conservative since no API Speci-fication 6A equipment failures have been attributed to
38、 brit-tle materials which met the requirements of the existingstandards.Therefore, the Task Group decided to start with a cleansheet and adopted the charge to Determine what is neces-sary to prevent brittle fracture in the field.Charge 4: With this charge in mind, the Task Group estab-lished work gr
39、oups for:a. Literature survey.b. Literature evaluation.c. Correlations and calculations.d. Position paper containing proposed changes.2 General History of API 6A/6D ActivitiesRelative to Impact Testing of Materials2.1 About 1969/70, at the API meeting in Los Angeles, acommittee was set up to review
40、the materials listed in APISpecification 6A and Specification 6D for low temperatureservice. This interest was generated by the activities of theAlaska Pipeline Project.2.2 The directions given by API committees were to re-view the materials listed in API Specification 6A and Speci-fication 6D and t
41、o remove those materials which would notmeet the standard Charpy V notch requirements of 15 ft-lbaverage, none less than 12 ft-lb at 20 F. The 20 F tem-perature was selected simply because that was the low end ofthe temperature range for API products at that time. In re-viewing these materials, it b
42、ecame very apparent to the com-mittee members that most of the materials listed would notmeet the standard Charpy requirements at 20 F and thatsome of the materials were even questionable above +32F.With this in mind, a call was put forth to all API membersto report and document, if possible, any fa
43、ilures of APIequipment which could be attributed to low notch toughness.No such failures were reported even in the Canadian or NorthSea sectors. Since no failures were reported, and since it waswell known that impact test values are generally consideredrelative in nature and are not used as a design
44、 tool, the com-mittee was put in a quandary as to what action should betaken. There was considerable discussion on how the indus-try would react to removing a material from the API specifi-cations which had been used very successfully for twenty orthirty years with no reported problems. and at the s
45、ame time,support its existence and continued use in the field.2.3 The final decision was to leave the need for impacttesting at temperatures above 20 F up to the users, whocould request impact testing at any temperature and stipulateany values they desired.Equipment below 20F would automatically req
46、uire im-pact testing. The test temperature and energy requirementshave changed somewhat over the years and have eventuallyevolved into the requirements of the current API Specifica-tion 6A and Specification 6D.Technical Report on Material Toughness3 Materials Toughness Task GroupHistory3.1 API Speci
47、fication 6A, Fifteenth Edition, was issued inApril 1986. There was immediate comment from Europe,specifically Great Britain and Norway, that their concernshad been ignored and that API Specification 6A equipmentwas inadequate for North Sea service. Three main areas ofdisagreement surfaced: Impact en
48、ergy value. Omission of a temperature rating specific to North Sea. No requirement for impact testing at service tempera-tures above 20F.These contentions arose despite the 15th Editions new,more stringent NDE requirements which reduce flaw size ac-ceptance and, therefore, reduce a materials ability
49、 to gener-ate a propagating crack.3.2 The committee was informed that the 15 ft-lb value at-tached to Charpy Impact Testing was the most troublesomeitem. This value was added to API Specification 6A in 1969to cull materials destined for Arctic service. The 1969 TaskGroups minutes indicate that they chose 15 ft-lb becauseASTM A350 and A352 listed this value for the most commonforging and casting materials of that time. Furthermore, the1969 version of A320 Gr L7M bolting required 15 ft-lb. Ap-parently, ASTM acquired the value from the Liberty Shipwork of
