1、Heat Treatment and Testing of Carbon and Low Alloy Steel Large Cross Section and Critical Section ComponentsAPI RECOMMENDED PRACTICE 6HT SECOND EDITION, JUNE 2013Special NotesAPI publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, an
2、d federal laws and regulations should be reviewed.Neither API nor any of APIs employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained
3、herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of APIs employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upo
4、n privately owned rights.API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publicat
5、ion and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any authorities having jurisdiction with which this publication may conflict.API publications are published to facilitate the broad availability of proven, sound engin
6、eering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using
7、any other practices.Any manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact c
8、onform to the applicable API standard.Users of this Recommended Practice should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein. All rights reserved. No part
9、of this work may be reproduced, translated, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 1220 L Street, NW, Washington, DC
10、 20005.Copyright 2013 American Petroleum InstituteForewordThis recommended practice was formulated by Subcommittee 6, Ad-Hoc Task Group under ISO Standard 10423 on Heat Treatment of Large Cross Section and Critical Section Components. It is a report of the conclusion of a task group study of heat tr
11、eatment as covered by API Specification 6A, Specification for Wellhead and Christmas Tree Equipment. Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by lette
12、rs patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the specification.Should: As used in a standard, “should” de
13、notes a recommendation or that which is advised but not required in order to conform to the specification. This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questio
14、ns concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, NW, Washington, DC 20005. Reques
15、ts for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this re
16、view cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 1220 L Street, NW, Washington, DC 20005.Suggested revisions are invited and should be submitted to the Stand
17、ards Department, API, 1220 L Street, NW, Washington, DC 20005, standardsapi.org.iiiContentsPage1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Normative References. . . . .
18、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Terms and Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Purpose
19、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20、 . . . . . . . . . . . . . . . . 26 Recommended Heat Treating Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21、 . . . . . . . . . . . . . . . . . . . . . . . . . . . 26.2 Requirements for Heat Treating Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36.3 Recommendations for Heat Treatment Procedures and Practices . . . . . . . . . . . . . . . . .
22、 . . . . . . . . . . . . . . . 56.4 Recommendations for QTCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Design Consideration and Material Selection Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . .
23、 . . . . . . . . . 9v1Heat Treatment and Testing of Carbon and Low Alloy Steel Large Cross Section and Critical Section Components1 ScopeThis recommended practice (RP) may supplement the API equipment specifications for carbon and low alloy steel large cross section and critical components. The reco
24、mmend practice described herein suggests the requirements for batch-type bath quench and water spray quench-type heat treating practices.2 Normative ReferencesStandards referenced in this specification may be replaced by other international or national standards that can be shown to meet or exceed t
25、he requirements of the referenced standard. Manufacturers who use other standards in lieu of standards referenced herein are responsible for documenting the equivalency of the standards. Referenced standards used by the manufacturer may be either the applicable revision shown in Section 2 and herein
26、 or the latest revision. When the latest edition is specified it may be used on issue and shall become mandatory six months from the date of the revision.API Specification 6A, Specification for Wellhead and Christmas Tree EquipmentASTM A2551, Standard Test Methods for Determining Hardenability of St
27、eelNACE MR0175 2/ISO 15156 3, Petroleum and natural gas industriesMaterials for use in H2S-containing environments in oil and gas productionSAE AMS-H-6875 4, Heat Treatment of Steel Raw Materials3 Terms and Definitions For the purposes of this document, the following definitions apply.3.1critical se
28、ction componentsAny part having a cross section thickness with an equivalent round (ER) that exceeds the depth of hardenability of the alloy selected for the part. 3.2large cross sectionAny part having a cross section thickness with an equivalent round (ER) greater than 5 in. (125 mm).3.3prolongatio
29、nAn extension of a piece of raw material or an extension of a production part made integrally during forging, hot working, cold working or casting for the purpose of performing mechanical testing and metallurgical evaluation.3.4QTCQualification test coupon.1ASTM International, 100 Barr Harbor Drive,
30、 West Conshohocken, Pennsylvania 19428, www.astm.org.2NACE International (formerly the National Association of Corrosion Engineers), 1440 South Creek Drive, Houston, Texas 77218-8340, www.nace.org.3International Organization for Standardization, 1, ch. de la Voie-Creuse, Case postale 56, CH-1211 Gen
31、eva 20, Switzerland, www.iso.org.4SAE International, 400 Commonwealth Drive, Warrendale, Pennsylvania 15096-0001, www.sae.org.2API RECOMMENDED PRACTICE 6HT3.5soak timeThe time that the entire part (throughout its cross section) is at the specified temperature.4 PurposeHeat treatment is a critical pr
32、ocess that must be appropriate and controlled in order to produce parts that comply with design requirements. Per API 6A, “The properties exhibited by the QTCs shall represent the properties of the thermal response of the material comprising the production parts it qualifies. Depending upon the hard
33、enability of a given material, the QTC results might not always correspond to the properties of the actual components at all locations throughout their cross section.” The specified mechanical properties may not necessarily be required or achieved through the entire section thickness of the producti
34、on part(s). These procedures are intended to provide the manufacturer and end user with a means of ensuring that the qualification test coupon (QTC) is more representative of the mechanical properties in a large cross section component than can be expected with a standard API equipment specification
35、 QTC. Furthermore, these procedures are intended to provide to optimize the heat treatment and heat treatment response of large cross section components, thereby insuring that the component has the required mechanical properties at the depth below the surface established by the manufacture at all cr
36、itical locations. It should be noted that the required mechanical properties as established by the manufacturer may be different from the mechanical properties required by the API equipment specification. This recommended practice is intended to supplement the heat treatment and testing requirements
37、 found in the API equipment specification and not to replace them altogether. 5 ApplicationThis recommended practice is intended for use on large cross section components being manufactured for conformance to API equipment specifications. 6 Recommended Heat Treating Practices6.1 GeneralHeat treating
38、 may be defined as the controlled heating and cooling of a metal in order to obtain a desired microstructure and consequently desired properties. Carbon and low alloy steels are the most widely used alloys in oil and gas exploration and production. One of the reasons for this is their versatility: a
39、 wide range of properties can be obtained through an appropriate heat treatment. The basis for heat treating carbon and low alloy steels is that they have several different stable crystal structures depending on the heat treatment process used. By transforming the crystal structures during heat trea
40、tment, the desired microstructure and mechanical properties can be obtained in the end product, provided the size of the product does not exceed the hardenability limits of the alloy.The most common type of heat treatment imposed on carbon and low alloy steels is a three- to four-step process consis
41、ting of austenitizing, quenching, and tempering (Q ladle analysis or product chemical analysis; description of the parts to be heat treated including the quantity; QTC requirements (see 6.4); qualification testing and acceptance criteria (e.g. mechanical properties, metallurgical requirements, and t
42、est method specifications); any restrictions on specific furnace size or type used, when applicable; heat treating times and temperatures for all cycles; quenching medium, including start and finish temperature limits for water; allowable methods of determining time at temperature for each cycle; al
43、lowable reheat treatment provisions for nonconforming material; hardness test method, locations, frequency, and acceptance criteria; any special requirements; certification and records requirements.6.3.2 Rough Machining PracticesMachining prior to heat treat should be considered to minimize the stoc
44、k remaining on parts made from carbon and low alloy steels with relatively low hardenability.Parts requiring rough machining prior to heat treatment shall have sharp corners radiused or chamfered prior to the austenitize and quench operation. Such radiused or chamfered corners help to prevent quench
45、 cracking in these areas.There should be generous radii on all corners of parts being heat treated to prevent quench cracking. A 1/8-in. (3-mm) radius is the minimum, but 1/4 in. (6 mm) or larger is recommended.Rough machining to within 1/8 in. (3 mm) to 1/2 in. (13 mm) per side of major finished di
46、mensions prior to heat treatment is recommended. Additional material may need to be left on the component for the following reasons: to prevent quench cracking; to allow for the removal of surface scale and decarburization; to allow for the removal of surface imperfections;6API RECOMMENDED PRACTICE
47、6HT to allow for the distortion of part geometry; to ensure cleanup to the finished dimensions during final machining.In some cases the placement or rough machining of internal through bores and/or internal part configuration bears on the selection of the appropriate alloy. Since the through bores a
48、nd internal configuration substantially reduce the section thickness, the hardenability of the alloy selected may be less than that required for the same part without the through bores. Contiguous thickness variations should be minimized to help prevent quench cracking. Larger section thicknesses qu
49、ench at a much different rate than do the smaller sections and create a potential for contractual stress cracking between the sections during the quench. A generous radius should be left between these section thicknesses prior to heat treatment. 6.3.3 Furnace Loading PracticesTo ensure that all parts are evenly heated and quenched, provide sufficient part spacing within the working zone of the furnace. Do not stack or bundle parts. Fixtures may be required.Parts should not be placed directly on the furnace hearth (floor). Use a metal tray or fixture that allows the furna
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