20-5_R2009_E1991.pdf

Copyrighted material licensed to Stanford University by Thomson Scientific(),downloaded on Oct-05-2010 by Stanford University User.No further reproduction or distribution is permitted.Uncontrolled when printed.REAFFIRMED 2009FOR CURRENT COMMITTEE PERSONNELPLEASE E-MAIL CSasme.orgNATIONAL STANDARD GAGING FOR DRYSEAL PIPE THREADS(INCH)ASME B1.20.5-1991(REVISION OF ANSI 81.20.5-1978)The American Society of Mechanical Engineers 345 East 47th Street,New York,N.Y.1001 7-Copyrighted material licensed to Stanford University by Thomson Scientific(),downloaded on Oct-05-2010 by Stanford University User.No further reproduction or distribution is permitted.Uncontrolled when printed.Date of Issuance:March 15,1991 This Standard will be revised when the Society approves the issuance of a new edition.There will be no addenda or written interpretations of the requirements of this Standard issued to this edition.ASME is the registered trademark of The American Society of Mechanical Engineers.This code or standard was developed under procedures accredited as meeting the criteria for American National Standards.The Consensus Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an oppor-tunity to participate.The proposed code or standard was made available for public review and comment which provides an opportunity for additional public input from industry,academia,reg-ulatory agencies,and the public-at-large.ASME does not approve,rate,or endorse any item,construction,proprietary device,or activity.ASME does not take any position with respect to the validity of any patent rights asserted in connection with any items mentioned in this document,and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable Letters Patent,nor assume any such liability.Users of a code or standard are expressly advised that determination of the validity of any such patent rights,and the risk of infringement of such rights,is entirely their own responsibility.Participation by federal agency representative(s)or person(s)affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard.ASME accepts responsibility for only those interpretations issued in accordance with governing ASME procedures and policies which preclude the issuance of interpretations by individual vol-unteers.No part of this document may be reproduced in any form,in an electronic retrieval system or otherwise,without the prior written permission of the publisher.Copyright 0 1991 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A.Copyrighted material licensed to Stanford University by Thomson Scientific(),downloaded on Oct-05-2010 by Stanford University User.No further reproduction or distribution is permitted.Uncontrolled when printed.(This Foreword is not part of ASME B1.20.5-1991.)In 1973,the American National Standards Committee B2,which had formerly been re-sponsible for pipe thread standards,was absorbed by ANSI Standards Committee B1 and reorganized as subcommittee 20.A complete rewrite of the B2.2-1968 Standard on Dryseal Pipe Threads was completed with the publication of ANSI B1.20.3-1976 for product threads and the ANSI B1.20.5-1978 Standard for Gaging.The product thread standard ANSI B1.20.3 establishes two classes of dryseal pipe threads:Class 1 and Class 2.The classes differ only in inspection requirements.With Class 1 threads,inspection of root and crest truncation is not specified.Class 2 threads are identical to Class 1 threads except that inspection of root and crest truncation is required.This gaging standard includes 6-step crest and root check gages,which,within their limitations,should be helpful in establishing the degree of conformance of product threads.When 6-step crest or root check gages are to be used,it is necessary to classify the product thread size into a size range(minimum,basic,or maximum)as shown in Fig.1.The use of 3-step L1 thread gages for NPTF threads requires estimating the one third of a turn,plus or minus,from the basic notch on the gage to classify the thread as basic.Use of this same one third turn estimation is required to determine minimum and maximum ranges.This Standard includes 4-step taper thread gages to eliminate the need for estimating the one third turn de-viation from basic necessary with 3-step or basic step gages.3-step taper thread gages are included in Appendix A for those who may prefer to use them.Crest and root check gages for NPTF threads are also covered in this Standard.Prior to the-publication of ANSI B1.20.5-1978 many gage manufacturers had calculated diameters for and made such gages based on methods used for ANPT (MIL-P-7105)6-step gages,which were calculated to the extremes of the minimum and maximum zones,where most product threads should never be,and which,further,is not the same logic used in calculating