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Prevention of Brittle Fracture of Pressure Vessels API RECOMMENDED PRACTICE 920 FIRST EDITION,MARCH 1990 American Petroleum Institute 1220 L Street,Northwest Nashington,D.C.20005 J?Prevention of Brittle Fracture of Pressure Vessels Refining Department API RECOMMENDED PRACTICE 920 FIRST EDITION,MARCH 1990 American Petroleum Institute SPECIAL NOTES 1.API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE.WITH RESPECT TO PARTICULAR CIRCUM-STANCES,LOCAL,STATE,AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED.2.API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS,MANUFACTURERS,OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES,AND OTHERS EXPOSED,CON-CERNING HEALTH AND SAFETY RISKS AND PRECAUTlONS,NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL,STATE,OR FEDERAL LAWS.3.INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPER PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDITIONS SHOULD BE OBTAINED FROM THE EMPLOYER,THE MANUFACTURER OR SUPPLIER OF THAT MATERIAL,OR THE MATERIAL SAFETY DATA SHEET.4.NOTHING CONTAINED IN ANY AP PUBLICATION IS TO BE CONSTRUED AS GRANTING ANY RIGHT,BY IMPLICATION OR OTHERWISE,FOR THE MANUFACTURE,SALE,OR USE OF ANY METHOD,APPARAI:US,OR PRODUCT COVERED BY LETTERS PATENT.NEITHER SHOULD ANYTHING CONTAINED IN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABILITY FOR INFRINGEMENT OF LETTERS PATENT.5.GENERALLY,API STANDARDS ARE REVIEWED AND REVISED,REAFFIRMED,OR WITHDRAWN.AT LEAST EVERY FIVE YEARS.SOMETIMES A ONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW CYCLE.THIS PUBLICATION WILL NO LONGER BE IN EFFECT FIVE YEARS AFfER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR,WHERE AN EXTENSION HAS BEEN GRANTED,UPON REPUBLICATION.STATUS OF THE PUBLICATION CAN BE ASCERTAINED FROM THE API AUTHORING DEPARTMENT(TELEPHONE(202)682-8000.A CATALOG OF API PUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API,1220 L STREET,N.W.,WASHINGTON,D.C.20005.Copyright 1990 American Petroleum Institute FOREWORD This recommended practice offers guidance in the selection of steels for new pressure vessels and the inspection and operation of existing pressure vessels to minimize the probability of brittle fracture.This recommended practice is aimed at preventing brittle fracture caused by low toughness at temperatures below approxi-mately 120F.Other mechanisms of deterioration a.re not addressed in this publi-cation.Both sections of this recommended practice are influenced by the improved toughness requirements voluntarily imposed by several companies for vessels used in refineries and by a few companies for petrochemical plants,natural gas process-ing plants,and transportation facilities.This recommended practice is also based on the toughness requirements included in the 1989 edition of Section VIII,Division 1,of the ASME Boiler and Pressure Vessel Code.The provision of API Standards 620 and 650 have also influenced the development of this recommended practice.Little precedent exists for the specification of enhanced toughness for multiple duplicate(or mass produced)vessels,nor for those vessels used in natural resource services(see Section 6 of API 510 for a more complete definition of the latter).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 publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal,state,or municipal regulation with which this publication may conflict.Suggested revisions are invited and should be submitted to the director of the Refining Department,American Petroleum Institute,1220 L Street,N.W.,Washington,D.C.20005.iii CONTENTS SECTION 1-SELECTION OF PRESSURE VESSEL STEELS TO PREVENT BRITTLE FRACTURE Page 1.1 Introduction.1 1.2 Purpose.1 1.3 General Philosophy.1 1.4 Materials Selection.1 1.5 Referenced Publications.2 SECTION 2-TOUGHNESS EVA.LUATION OF EXISTING PRESSURE VESSELS.2.1 Introduction.t:2.4 General Philosophy.2.5 Criteria for Service.;._.2.6 Importance of Condition.2 2 2 3 4 4 APPENDIX A-HYDROSTATIC TESTING.5 APPENDIX B-STEELS.7 APPENDIX C-INSPECTION.9 APPENDIX D-IMPACT TEST EXEMPTION CURVES.11 Figure D-1-Material Curves.12 Table D-1-Impact Test Exemption Temperatures for Bolting Materials.13 V Prevention of Brittle Fracture of Pressure Vessels SECTION 1-SELECTION OF PRESSURE VESSEL STEELS TO PREVENT BRITTLE FRACTURE 1.1 Introduction 1.1.1 Pressure vessels have failed by brittle fracture when the steel used did not have sufficient toughness for the exposure conditions.In the majority of cases,the failures occurred during the hydrostatic test(bydrote st)of the vessel and were triggered by discontinuities intro-duced during fabrication.Special toughness require-ments have voluntarily been appli