1、RecommendedPractices for Welding ofChromium-MolybdenumSteel Piping andTubingANSI/AWS D10.8-96An American National Standard550 N.W. LeJeune Road, Miami, Florida 33126ANSI/AWS D10.8-96An American National StandardApproved byAmerican National Standards InstituteDateRecommended Practices for Welding of
2、Chromium-Molybdenum Steel Piping and TubingSupersedes AWS D10.8-86Prepared by AWS Committee on Piping and TubingUnder the Direction of AWS Technical Activities CommitteeApproved by AWS Board of DirectorsAbstractThis document presents recommendations for welding chromium-molybdenum steel pipe and tub
3、ing to itself and to various other materials. Subjects covered in detail are filler metal selection, joint design, preheating, and postheating. Particular emphasis is placed on the importance of maintaining interpass temperature and dangers inherent in interrupted heating cycles.Key Words Chromium-m
4、olybdenum steel pipe, chromium-molybdenum steel tubingStatement on Use of AWS StandardsAll standards (codes, specifications, recommended practices, methods, classifications, and guides) of the American Welding Society are voluntary consensus standards that have been developed in accordance with the
5、rules of the Ameri-can National Standards Institute. When AWS standards are either incorporated in, or made part of, documents that are in-cluded in federal or state laws and regulations, or the regulations of other governmental bodies, their provisions carry the full legal authority of the statute.
6、 In such cases, any changes in those AWS standards must be approved by the govern-mental body having statutory jurisdiction before they can become a part of those laws and regulations. In all cases, these standards carry the full legal authority of the contract or other document that invokes the AWS
7、 standards. Where this contractual relationship exists, changes in or deviations from requirements of an AWS standard must be by agreement between the contracting parties.International Standard Book Number: 0-87171-500-7American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126 1996 by America
8、n Welding Society. All rights reserved Printed in the United States of AmericaNote: The primary purpose of AWS is to serve and benefit its members. To this end, AWS provides a forum for the ex-change, consideration, and discussion of ideas and proposals that are relevant to the welding industry and
9、the consensus of which forms the basis for these standards. By providing such a forum, AWS does not assume any duties to which a user of these standards may be required to adhere. By publishing this standard, the American Welding Society does not insure anyone using the information it contains again
10、st any liability arising from that use. Publication of a standard by the American Welding Society does not carry with it any right to make, use, or sell any patented items. Users of the in-formation in this standard should make an independent, substantiating investigation of the validity of that inf
11、ormation for their particular use and the patent status of any item referred to herein.With regard to technical inquiries made concerning AWS standards, oral opinions on AWS standards may be rendered. However, such opinions represent only the personal opinions of the particular individuals giving th
12、em. These individuals do not speak on behalf of AWS, nor do these oral opinions constitute official or unofficial opinions or interpretations of AWS. In addition, oral opinions are informal and should not be used as a substitute for an official interpretation.This standard is subject to revision at
13、any time by the AWS Piping and Tubing Committee. It must be reviewed every five years and if not revised, it must be either reapproved or withdrawn. Comments (recommendations, additions, or de-letions) and any pertinent data that may be of use in improving this standard are requested and should be a
14、ddressed to AWS Headquarters. Such comments will receive careful consideration by the AWS Piping and Tubing Committee and the author of the comments will be informed of the Committees response to the comments. Guests are invited to attend all meetings of the AWS Piping and Tubing Committee to expres
15、s their comments verbally. Procedures for appeal of an adverse decision concerning all such comments are provided in the Rules of Operation of the Technical Activities Com-mittee. A copy of these Rules can be obtained from the American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126.iii*Advi
16、sor*DeceasedPersonnelAWS Committee on Piping and TubingW. L. Ballis, Chairman Columbia Gas DistributionW. J. Sperko, 1st Vice Chairman Sperko Engineering ServicesM. C. Shepard, 2nd Vice Chairman Litwin Engineers and ConstructorsJ. K. Lambert, Secretary American Welding SocietyF. G. Ar m a o Aluminum
17、 Company of AmericaC. R. Brashears Alyeska Pipeline Service CompanyD. J. Connell Detroit EdisonH. W. Ebert Exxon Research and Engineering CompanyW. R. Etie ConsultantJ. E. Fisher INSECOE. A. Harwart* ConsultantG. K. Hickox ConsultantJ. Hill Hill Technical Services, IncorporatedJ. E. Hinkel Lincoln E
18、lectricConsultantR. B. Kadiyala* Techalloy CompanyM. P. Lang U. A. Local 514L. A. Maier, Jr. ConsultantB. B. McDonald United AssociationJ. W. McEnerney Cooperheat, IncorporatedJ. W. Moeller* ConsultantW. Newell Newell and AssociatesJ. S. Pastorok Perry Nuclear Power PlantL. Seum Phoenix ServicesCons
19、ultantE. G. Shifrin* ConsultantG. K. Sosnin ConsultantP. A . Te w s CRC-Evans Automatic WeldingJ. Tidwell Fluor DanielG. J. Tucker AIM Testing LaboratoryW. D. Watson, Jr. Roberts EngineeringR. R. Wright Moody-Tottrup International, IncorporatedAWS Subcommittee on Chromium-Molybdenum Steel PipingH. W
20、. Ebert, Chairman Exxon Research and Engineering CompanyJ. K. Lambert, Secretary American Welding SocietyD. J. Connell Detroit EdisonW. R. Etie ConsultantE. A. Harwart* ConsultantR. B. Kadiyala* Techalloy CompanyJ. W. McEnerney Cooperheat, IncorporatedL. Seum Phoenix ServicesConsultantW. Newell Newe
21、ll and AssociatesM. C. Shepard Litwin Engineers and ConstructorsW. J. Sperko Sperko Engineering ServicesJ. Tidwell Fluor DanielivForeword(This Foreword is not a part of ANSI/AWS D10.8-96, Recommended Practices for Welding of Chromium-Molybdenum Steel Piping and Tubing, but is included for informatio
22、n purposes only).The chromium-molybdenum (Cr-Mo) steels considered in this document contain from one-half to nine percent chromium and some molybdenum. These elements increase the corrosion and oxidation resistance of steel and impart greater strength and microstructural stability at elevated temper
23、atures.Since such alloy additions also increase hardenability, steps must be taken to prevent cracking during and after solid-ification by reducing stresses, limiting hydrogen content, and assuring adequate ductility. These steps include limiting the addition of those elements which increase hardena
24、bility, preheating, using filler metals and processes which mini-mize the addition of hydrogen to the weld, and postweld heat treatment (PWHT).When these alloys are used in a corrosive environment, care should be taken to eliminate crevices and reduce hardness. When the service conditions include ex
25、posure to high temperatures, consideration must also be given to the need for increased creep strength and possible problems due to temper embrittlement and stresses resulting from differential ther-mal expansion. In addition, when joining different chromium-molybdenum steels to each other or to aus
26、tenitic chromium-nickel stainless steels, consideration must be given to dilution during welding, diffusion of elements during service, and differences in thermal expansion and corrosion resistance.The selection of base metals is beyond the scope of this document; however, the selection of filler me
27、tals for various base metal combinations and suggested preheating and postweld heat treating temperatures are included. This recom-mended practice discusses the special considerations which are advisable when preheating and post heating. A more complete treatment of this subject is to be found in AN
28、SI/AWS D10.10, Recommended Practices for Local Heating of Welds in Piping and Tubing. Also not discussed in detail are the methods of root-pass welding. These are treated fully in ANSI/AWS D10.11, Recommended Practices for Root Pass Welding of Pipe Without Backing.Comments and suggestions are welcom
29、e. They should be addressed to the Secretary, Committee on Piping and Tubing, American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126.vTable of ContentsPage No.Personnel iiiForeword ivList of Tables .viList of Figures .vi1. Scope .12. Base Metals .12.1 General.12.2 Base-Metal Addition23. Fi
30、ller Metals 23.1 General.23.2 Low Hydrogen.23.3 Backing Rings and Consumable Inserts 43.4 Applications.43.5 Other Filler Metals.54. Joint Design and Preparation.54.1 Standard Joint Preparations .54.2 Root-Pass Considerations 54.3 Fit-Up.55. Preheating55.1 General.55.2 Interruption of Heating Cycle65
31、.3 Moisture and Other Materials Containing Hydrogen 75.4 Joint Restraint 75.5 Mass of the Base Metal76. Postweld Heat Treatment (PWHT) .76.1 General.76.2 PWHT Temperatures .76.3 PWHT Holding Time.76.4 Heating and Cooling86.5 Local PWHT86.6 Quality Control of PWHT .97. Repair and Maintenance Welding
32、of Service Exposed Cr-Mo Piping and Tubing.97.1 Base-Metal Contamination 97.2 Temper Embrittlement.97.3 Relaxation of PWHT Requirements 108. Safe Practices 10Annex A List of Safety Related References11Document List.12viList of TablesTable Page No.1 Base Metal Abbreviations12 Suggested Filler Metals
33、for Various Base Metal Combinations 33 Suggested Minimum Preheat Temperatures for Various Base Metals.64 Suggested PWHT Temperature Ranges.8List of FiguresFigure Page No.1 ASME B31.1 and B31.3 Bandwidth Requirement for Local PWHT 911. ScopeThese recommended practices apply to the arc weld-ing of the
34、 following base-metal combinations:(1) Similar chromium-molybdenum steels(2) Dissimilar chromium-molybdenum steels(3) Chromium-molybdenum to austenitic chromium-nickel stainless steels(4) Chromium-molybdenum to either carbon or carbon-molybdenum steelsIn this document, the chromium-molybdenum steel
35、al-loys are referred to as Cr-Mo steels.Cr-Mo steels are used extensively in the power, chem-ical, and petroleum industries. The properties of such piping and tubing materials and the applicable fabrica-tion and inspection requirements are addressed in a wide range of documents, including:(1) ASTM M
36、aterial Specifications(2) ASME Codes for Pressure Piping, B31(a) Power Piping (ANSI/ASME B31.1)(b) Chemical Plant and Petroleum Refinery Pip-ing (ANSI/ASME B31.3)(3) ASME Boiler and Pressure Vessel Codes (Sec-tions I, IIA, IIC, VIII, and IX)(4) NBIC National Board Inspection Code for Boilers and Pre
37、ssure Vessels (ANSI/NB-23)(5) API Piping Inspection Code (Inspection, Repair, Alteration and Rerating of In-Service Piping Systems), (API 570).2. Base Metals2.1 General. Table 1 lists the types of steel considered and the nominal chemical compositions and abbrevia-tions by which they will be identif
38、ied in this document. If materials not listed in Table 1 are used, the contents of this document may not apply. This will be especially true if the hardenability is increased by the presence of a higher carbon content. The carbon content of the materi-als listed is usually below 0.15 percent.The pri
39、mary factors governing the choice of filler metals are the composition of the base metals to be joined and the service conditions of the system. Gener-ally, the filler metal composition and the mechanical properties of the deposited weld metal should match Table 1Base Metal AbbreviationsTypes of Ste
40、elNominal CompositionASME/ASTM/ Grade* AbbreviationCarbon Steel (less than 0.35% C) A, B, or C C-steelCarbon1/2% Mo P1 or T1 C-Mo1/2% Cr1/2% Mo P2 or T2 1/2 Cr-Mo1% Cr1/2% Mo P12 or T12 1 Cr-Mo1-1/4% Cr1/2% Mo P11 or T11 1-1/4 Cr-Mo2% Cr1/2% Mo T3b 2 Cr-Mo2-1/4% Cr1% Mo P22 or T22 2-1/4 Cr-Mo3% Cr1%
41、 Mo P21 or T21 3 Cr-Mo5% Cr1/2% Mo P5 or T5 5 Cr-Mo7% Cr1/2% Mo P7 or T7 7 Cr-Mo9% Cr1% Mo P9 or T9 9 Cr-Mo9% Cr1% Mo-V, Nb, and N P91 or T91 9Cr-Mo-V18% Cr8% Ni TP-304 304 S. S.18% Cr12% Ni-Mo TP-316 316 S. S.18% Cr10% Ni-Nb (Cb) TP-347 347 S. S.18% Cr10% Ni-Ti TP-321 321 S. S.25% Cr20% Ni TP-310 3
42、10 S. S.*Table uses Symbols P (pipe), T (tube), and TP (tube or pipe). Other product forms with same nominal chemistry for which this document applies are CP (cast pipe), F (forging), FP (forged pipe), and WP (welded pipe).Recommended Practices for Welding ofChromium-Molybdenum Steel Piping and Tubi
43、ng2those of the base metals as closely as possible. Where service includes corrosion or oxidation, the corrosion and oxidation characteristics of the base metals and the weld deposit should be either matched as closely as pos-sible or selected to minimize galvanic reaction.2.2 Base-Metal Addition. S
44、ince the last edition of this recommended practice, one new Cr-Mo alloy has been added. It has a nominal composition of 9% Cr and 1% Mo, but vanadium, niobium (columbium), and nitrogen have been added to improve mechanical properties and corrosion resistance at elevated temperatures. This new materi
45、al has been assigned the grade designation of P91 and T91. Its weldability is similar to that of conventional 9 Cr-Mo materials. Special filler metals have been devel-oped for some welding processes.3. Filler Metals3.1 General. Suggested filler metals for various base-metal combinations are shown in
46、 Table 2. The filler met-als in this table are listed in accordance with the AWS classifications for electrodes and rods for the shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux cored arc welding (FCAW) processes. The classifications of fille
47、r metals for other processes will be in accordance with the specifications for those specific processes.Until recently the 5, 7, and 9 Cr-Mo electrodes and filler metals had been included in the same AWS filler metal specifications as austenitic stainless steels and had been assigned classifications
48、 such as E502. Recognizing that these filler metals are basically low-alloy steels, their classifications have been transferred to AWSs low-alloy filler metal specifications and have been assigned classifications such as E8018-B6. During these transition years, welding procedures and filler metal in
49、ventories can be expected to use both classifications. For the convenience of the user, Table 2 of this document lists these electrodes with their respective old and new classifications.Cr-Mo piping systems are usually selected for corro-sion resistance, high-temperature creep strength, or both. Since corrosion resistance is often associated with maxi-mum hardness, low-carbon electrodes (e.g., E8018-B3L), which are less air hardenable, are frequently se-lected for such applications. However, if high-tempera-ture creep resistance is a major design consideration, mini
