API RP 575 Inspection of Atmospheric an Low-Pressure Storage Tanks

Risk-based Inspection

API RECOMMENDED PRACTICE 580 FIRST EDITION, MAY 2002 ` , , ` , ` , , ` , , ` ` , ` , ` ` ` ` , , ` , , , ` , , , , , , ` , , ` ` , , ` -

COPYRIGHT 2003; American Petroleum Institute

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Risk-based Inspection

Downstream Segment API RECOMMENDED PRACTICE 580 FIRST EDITION, MAY 2002

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SPECIAL NOTES API publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed. 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, concerning health and safety risks and precautions, nor undertaking their obligations under local, state, or federal laws. 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. 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 letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent. Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years.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 after 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 Standards 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, www.api.org. 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. Questions concerning the interpretation of the content of this standard or comments and questions concerning the procedures under which this standard was developed should be directed in writing to the director, Standards Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005, [email protected]. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the general manager. API standards are published to facilitate the broad availability of proven, sound engineering and operating practices. These standards are not intended to obviate the need for applying sound engineering judgment regarding when and where these standards should be utilized. The formulation and publication of API standards is not intended in any way to inhibit anyone from using 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 conform to the applicable API standard.

All rights rights reserve reserved. d. No part part of this work work may be repr reproduced oduced,, stored stored in a retriev retrieval al system, system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written w ritten permission from the publisher. publisher. Contact the Publisher, API Publishing Publishing Services, Services, 1220 1220 L Street, Street, N.W., N.W., Washing Washington, ton, D.C. 20005. Copyright © 2002 American Petroleum Institute

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FOREWORD

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This recommended practice is intended to provide guidance on developing a risk-based inspection (RBI) program on fixed equipment and piping in the hydrocarbon and chemical process industries. It includes: • What is RBI • Wh What at are are the the key key ele eleme ment ntss of RBI • How How to impl implem emen entt a RBI RBI pro progr gram am It is based on knowledge and experience of engineers, inspectors, risk analysts and other personnel in the hydrocarbon and chemical industry. RP 580 is intended to supplement API 510 Pressure Vessel Inspection Code , API 570 Piping Inspection Code and API 653 Tank Inspection, Repair, Alteration and Reconstruction . These API inspection codes and standards allow an owner/user latitude to plan an inspection strategy and increase or decrease the code designated inspection frequencies based on the results of a RBI assessment. The assessment must systematically evaluate both the probability of failure and the associated consequence of failure. The probability of failure assessment must be based on all forms of deterioration that could reasonably be expected to affect the piece of equipment in the particular service. Refer to the appropriate code for other RBI assessment requirements. RP 580 is intended to serve as a guide for users in properly performing such a RBI assessment. The information in this recommended practice does not constitute and should not be construed as a code of rules, regulations, or minimum safe practices. The practices described in this publication are not intended to supplant other practices that have proven satisfactory, satisfactory, nor is this publication intended to discourage innovation and originality in the inspection of hydrocarbon and chemical facilities. Users of this recommended practice are reminded that no book or manual is a substitute for the judgment of a responsible, qualified inspector or engineer. 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, Standards Department, American Petroleum Institute, 1220 L Street, N.W., Washington D.C. 20005, [email protected].

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CONTENTS Page

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1

INTRODU INTRODUCTIO CTION, N, PURPOS PURPOSE E AND SCOPE SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .1 1.1 Purpos Purpose. e. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 1.2 Scope Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 . 1.3 Target arget Audienc Audiencee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2

REFERENC REFERENCES ES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. 2.1 Refere Reference nced d Public Publicati ations ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .3 2.2 Other Other Refer Referenc ences es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

3

DEFINIT DEFINITIONS IONS AND ACRON ACRONYMS YMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .4 3.1 Definit Definition ionss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 3.2 Acrony Acronyms. ms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 .

4

BASIC BASIC CONCEPT CONCEPTS S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 4.1 What What is Risk? Risk? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 4.2 Risk Risk Manage Managemen mentt and Risk Risk Reduct Reduction. ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 .7 4.3 The Evol Evoluti ution on of Inspec Inspectio tion n Interv Intervals als . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 .7 4.4 Inspec Inspectio tion n Optimi Optimizat zation. ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 .8 4.5 Relati Relative ve Risk Risk vs. Absolut Absolutee Risk. Risk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

5

INTRODU INTRODUCTIO CTION N TO RISK-B RISK-BASED ASED INSPECTI INSPECTION. ON. . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1 Conseq Consequenc uencee and Prob Probabi abilit lity y for Risk Risk-Ba -Based sed Insp Inspect ection. ion. . . . . . . . . . . . . . . . . . . 8 5.2 Types ypes of RBI RBI Assess Assessmen mentt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 .9 5.3 Precis Precision ion vs. vs. Accurac Accuracy. y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 .11 5.4 Unders Understan tandin ding g How RBI RBI Can Can Help Help to Manage Manage Operati Operating ng Risks Risks . . . . . . . . . . . . 11 5.5 Manage Managemen mentt of Risk Riskss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 .12 5.6 Relationship Relationship Between RBI and and Other Other Risk-Ba Risk-Based sed and and Safety Safety Initiativ Initiatives es . . . . . 12 5.7 Relationship Relationship with Jurisdi Jurisdictiona ctionall Requiremen Requirements. ts. . . . . . . . . . . . . . . . . . . . . . . . . . 13

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PLANNING PLANNING THE RBI RBI ASSESS ASSESSMENT. MENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 .13 6.1 Gettin Getting g Start Started ed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 13 6.2 Establ Establish ishing ing Obje Objecti ctives ves and and Goals Goals of of a RBI Assess Assessmen mentt . . . . . . . . . . . . . . . . . . 13 6.3 Initia Initiall Screen Screening. ing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 .14 6.4 Establ Establish ish Operati Operating ng Bounda Boundarie riess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 .16 6.5 Select Selecting ing a Type of of RBI Assess Assessmen ment. t. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 .16 6.6 Estima Estimatin ting g Resour Resources ces and Time Time Requi Required red . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 . 17

7

DATA AND INFORMAT INFORMATION ION COLLECTI COLLECTION ON FOR FOR RBI RBI ASSES ASSESSMEN SMENT T . . . . . . . 17 7.1 RBI Data Data Needs Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 17 7.2 Data Data Qualit Quality y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 18 7.3 Codes Codes and and Standa Standards rds—Na —Natio tional nal and and Inter Internat nation ional. al. . . . . . . . . . . . . . . . . . . . . . . 18 7.4 Source Sourcess of Site Site Spec Specific ific Data Data and Info Informa rmatio tion n . . . . . . . . . . . . . . . . . . . . . . . . . . 18

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IDENTIF IDENTIFYING YING DETERIOR DETERIORATI ATION ON MECHA MECHANISM NISMS S AND AND FAILUR FAILURE E MODES MODES . . 19 8.1 Introd Introduct uction ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 19 8.2 Failure Failure and Failure Failure Modes Modes for Risk-Based Risk-Based Inspecti Inspection on . . . . . . . . . . . . . . . . . . . . 19 8.3 Deteri Deteriora oratio tion n Mechan Mechanism isms. s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 .19 8.4 Other Other Fail Failure ures. s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 20

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ASSESSI ASSESSING NG PROBABI PROBABILITY LITY OF FAILU FAILURE RE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 .20 9.1 Introd Introduct uction ion to to Probab Probabili ility ty Analys Analysis is . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 9.2 Units Units of Meas Measure ure in in the Prob Probabi abilit lity y of Fail Failure ure Analysi Analysis. s. . . . . . . . . . . . . . . . . . . 20 9.3 Types ypes of Prob Probabi abilit lity y Anal Analysi ysiss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 .21 9.4 Determ Determina inatio tion n of Prob Probabi abilit lity y of Fail Failure ure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

10 ASSESSI ASSESSING NG CONSEQU CONSEQUENCE ENCES S OF FAILUR FAILURE E . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 .23 10.1 Introductio Introduction n to Consequence Consequence Analysis Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 10.2 Types of Consequence Consequence Analysis Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 .23 10.3 Units of Measure Measure in Consequence Consequence Analysis Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 10.4 Volume of of Fluid Release Released d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 .24 10.5 Consequence Consequence Effect Effect Catego Categories ries.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 .25 11 RISK RISK DETERMI DETERMINATI NATION, ON, ASSESS ASSESSMEN MENT T AND MANAGE MANAGEMENT. MENT. . . . . . . . . . . . 26 11.1 Purpose Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 26 11.2 Determinatio Determination n of Risk Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 .26 11.3 Risk Manageme Management nt Decisions Decisions and Acceptable Acceptable Levels Levels of Risk. . . . . . . . . . . . . . . 28 11.4 Sensitivi Sensitivity ty Analysi Analysiss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 .28 11.5 Assumptions. Assumptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 28 11.6 Risk Present Presentation ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 .29 11.7 Establishin Establishing g Accepta Acceptable ble Risk Risk Thresholds Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 11.8 Risk Managem Management ent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 30 12 RISK RISK MANAGEM MANAGEMENT ENT WITH WITH INSPEC INSPECTION TION ACTI ACTIVITI VITIES ES . . . . . . . . . . . . . . . . . . 30 12.1 Managing Managing Risk by Reducing Reducing Uncertainty Uncertainty Through Through Inspect Inspection ion . . . . . . . . . . . . . 30 12.2 Identifying Identifying Risk Risk Manageme Management nt Opportuniti Opportunities es from from RBI and Probabilit Probability y of Failure Failure Results Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 12.3 Establishin Establishing g an Inspection Inspection Strate Strategy gy Based on on Risk Assessment Assessment . . . . . . . . . . . . 31 12.4 Managing Managing Risk with Inspecti Inspection on Activities Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 . 31 12.5 Managing Managing Inspection Inspection Costs with with RBI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 . 32 12.6 Assessing Assessing Inspectio Inspection n Results Results and Determini Determining ng Correcti Corrective ve Action . . . . . . . . . . 32 12.7 Achieving Achieving Lowest Lowest Life Life Cycle Costs Costs with with RBI . . . . . . . . . . . . . . . . . . . . . . . . . . 32 13 OTHER OTHER RISK MITI MITIGATI GATION ON ACTIVI ACTIVITIE TIES S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 13.1 Genera Generall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 32 13.2 Equipment Equipment Replacem Replacement ent and Repair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 .33 13.3 Evaluating Evaluating Flaws Flaws for for Fitness-fo Fitness-forr- Service. Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 13.4 Equipment Equipment Modificat Modification, ion, Redesign Redesign and Rerating. Rerating. . . . . . . . . . . . . . . . . . . . . . . . 33 13.5 Emergency Emergency Isolation Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 .33 13.6 Emergency Emergency Depressurizi Depressurizing/Deng/De-inv inventor entory y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 13.7 Modify Modify Process Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 .33 13.8 Reduce Inventory Inventory.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 .33 13.9 Water Spray/D Spray/Deluge. eluge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 .33 13.10 Water Curtain Curtain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 .33 13.11 Blast-Resist Blast-Resistant ant Constructi Construction on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 . 33 13.12 Others. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 34

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vi Document provided by IHS Licensee=YPF/5915794100, Licensee=YPF/5915794100, User=, 11/11/2003 10:40:41 MST Questions or comments about this message: please call the Document Policy Group at 1-800-451-1584.

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14 REASSESS REASSESSMENT MENT AND UPDAT UPDATING ING RBI RBI ASSESS ASSESSMENT MENTS S . . . . . . . . . . . . . . . . . .34 . 34 14.1 RBI Reassessm Reassessments ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 .34 14.2 Why Conduct Conduct a RBI Reassessm Reassessment? ent? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 .34 14.3 When to to Conduct Conduct a RBI Reassessment. Reassessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 .35 15 ROLES, ROLES, RESPONSI RESPONSIBILI BILITIES TIES,, TRAINING TRAINING AND AND QUALIFIC QUALIFICATIO ATIONS NS . . . . . . . . . 35 15.1 Team Approach Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 35 15.2 Team Members, Members, Roles Roles & Responsibi Responsibilitie litiess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 15.3 Training Training and and Qualification Qualificationss For RBI Application. Application. . . . . . . . . . . . . . . . . . . . . . . . 36 16 RBI DOCUME DOCUMENTAT NTATION ION AND AND RECORDRECORD-KEEP KEEPING ING . . . . . . . . . . . . . . . . . . . . . . .37 . 37 16.1 Genera Generall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 37 16.2 RBI Methodolo Methodology gy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 16.3 RBI Personnel Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 37 16.4 Time Time Frame Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 37 16.5 Assignment Assignment of of Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 .37 16.6 Assumptions Assumptions Made to Assess Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 . 37 16.7 Risk Assessment Assessment Results Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 16.8 Mitigation Mitigation and FollowFollow-up up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38 .38 16.9 Codes, Standar Standards ds and Government Government Regulations Regulations.. . . . . . . . . . . . . . . . . . . . . . . . . 38 APPENDIX APPENDIX A Figures 1 2 3 4 5 6

DETERIO DETERIORATI RATION ON MECHAN MECHANISM ISMS S . . . . . . . . . . . . . . . . . . . . . . . . . . .39 .39

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Managem Management ent of Risk Risk Using Using RBI. RBI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 .8 Risk Risk Plot Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Contin Continuum uum of RBI RBI Approac Approaches. hes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 .10 Risk-b Risk-base ased d Inspe Inspecti ction on Plan Plannin ning g Proce Process ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 .11 Exam Exampl plee Even Eventt Tre Treee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 28 Exampl Examplee Risk Risk Matr Matrix ix Usin Using g Proba Probabil bility ity and Consequ Consequenc encee Cate Categor gories ies to Display Risk Rankings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 .29 Risk Risk Plot Plot when when Using Using Quantit Quantitati ative ve or or Numeri Numericc Risk Risk Valu Values es . . . . . . . . . . . . . . . . . 30

Tables 1 2 3 4

Thin Thinni ning ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39 39 Stre Stress ss Cor Corro rosi sion on Cra Crack ckin ing g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 .41 Metall Metallur urgic gical al and and Envir Environm onment ental al Fail Failure uress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Mech Mechani anica call Fai Failu lure ress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 45

vii COPYRIGHT 2003; American Petroleum Institute


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Risk-based Inspection 1 Intro Introdu ducti ction on,, Purpo Purpose se and Scope Scope

1.1.1 1.1 .1 Key Key Elem Element ents s of a RBI RBI Pro Progra gram m Key elements that should exist in any RBI program are:

1.1 PURPOSE

a. Management Management systems systems for maintaining maintaining documenta documentation, tion, perpersonnel qualifications, data requirements and analysis updates. b. Documented Documented method method for probabili probability ty of failure failure determination. c. Documented Documented method method for consequen consequence ce of failure failure determination. d. Documented Documented methodolo methodology gy for managing managing risk through through inspection and other mitigation activities.

The purpose of this document is to provide users with the basic elements for developing and implementing a risk-based inspection (RBI) program. The methodology is presented in a step-by-step manner to the maximum extent practicable. Items covered are: a. An introductio introduction n to the concepts concepts and princip principles les of riskriskbased inspection for risk management; and b. Individual Individual sections sections that describe describe the steps steps in applying these principles within the framework of the RBI process:

However, all the elements outlined in 1.1 should be adequately addressed in RBI applications, in accordance with the recommended practices in this document.

1. Planning Planning the the RBI Assessment. Assessment. 2. Data and and Informati Information on Collectio Collection. n. 3. Identifying Identifying Deteriorat Deterioration ion Mechanisms Mechanisms and Failure Failure Modes. 4. Assessing Assessing Probabil Probability ity of of Failure. Failure. 5. Assessing Assessing Conseque Consequence nce of Failure. Failure. 6. Risk Determinat Determination, ion, Assessm Assessment ent and Management. Management. 7. Risk Management Management with with Inspection Inspection Activi Activities. ties. 8. Other Risk Risk Mitigatio Mitigation n Activi Activities. ties. 9. Reassessment Reassessment and Updating. Updating. 10. Roles, Responsibil Responsibilities, ities, Trainin Training g and Qualificatio Qualifications. ns. 11. Documentatio Documentation n and record-keep record-keeping. ing. The expected outcome from the application of the RBI RB I process should be the linkage of risks with appropriate inspection or other risk mitigation activities to manage the risks. The RBI process is capable of generating:

1.1.2 1.1 .2 RBI Benefit Benefits s and and Limita Limitatio tions ns The primary work products of the RBI assessment and management approach are plans that address ways to manage risks on an equipment level. level. These equipment plans highlight risks from a safety/health/environment perspective and/or from an economic standpoint. In these plans, cost-effective actions for risk mitigation are recommended along with the resulting level of risk mitigation expected. Implementation of these plans provides one of the following: a. An overall overall reduction reduction in risk risk for the facilitie facilitiess and equipment assessed. b. An acceptance/un acceptance/underst derstanding anding of the current current risk. risk. The RBI plans also identify equipment that does not require inspection or some other form of mitigation because of the acceptable level of risk associated with the equipment’s current operation. In this way, inspection and maintenance activities can be focused and more cost effective. This often results in a significant reduction in the amount of inspection data that is collected. This focus on a smaller set of data should result in more accurate information. In some cases, in addition to risk reductions and process safety improvements, RBI plans may result in cost reductions. RBI is based on sound, proven risk assessment and management principles. principles. Nonetheless, RBI will not compensate compensate for:

a. A ranking ranking by risk of of all equipment equipment evaluate evaluated. d. b. A detailed detailed description description of the the inspection inspection plan to be employed for each equipment item, including: 1. Inspection Inspection method(s) method(s) that that should be used used (e.g., visual, visual, UT, Radiography, WFMT). 2. Extent of applicat application ion of the inspection inspection method(s method(s)) (e.g., percent of total area examined or specific locations). 3. Timing Timing of inspection inspections/ex s/examinat aminations. ions. 4. Risk management management achieved achieved through through implementa implementation tion of the inspection plan. c. A description description of any other risk risk mitigation mitigation activitie activitiess (such as repairs, replacements or safety equipment upgrades). d. The expected expected risk levels levels of all equipment equipment after after the inspecinspection plan and other risk mitigation activities have been implemented.

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a. b. c. d. e. f.

Inaccurate Inaccurate or missing missing information. information. Inadequate Inadequate designs designs or faulty equipment equipment installation installation.. Operating Operating outside outside the acceptable acceptable design design envelope. envelope. Not effecti effectively vely execut executing ing the plans. plans. Lack of qualified qualified personnel personnel or or teamwork. teamwork. Lack of sound enginee engineering ring or operational operational judgment. judgment.

1 Document provided by IHS Licensee=YPF/5915794100, Licensee=YPF/5915794100, User=, 11/11/2003 10:40:41 MST Questions or comments about this message: please call the Document Policy Group at 1-800-451-1584.

2

API RECOMMENDED PRACTICE 580

1.1.3 1.1 .3 Using Using RBI RBI as a Contin Continuou uous s Improv Improveme ement nt Tool Utilization of RBI provides a vehicle for continuously improving the inspection of facilities and systematically reducing the risk associated with pressure boundary failures. As new data (such as inspection results) becomes available or when changes occur, reassessment of the RBI program can be made that will provide a refreshed view of the risks. Risk management plans should then be adjusted appropriately. RBI offers the added advantage of identifying gaps or shortcomings in the effectiveness of commercially available inspection technologies and applications. In cases where technology cannot adequately and/or cost-effectively mitigate risks, other risk mitigation approaches can be implemented. RBI should serve to guide the direction of inspection technology development, and hopefully promote a faster and broader deployment of emerging inspection technologies as well as proven inspection technologies that may be available but are underutilized. ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

1.1.4 1.1 .4 RBI as an Inte Integra grated ted Manag Manageme ement nt Tool ool RBI is a risk assessment and management tool that addresses an area not completely addressed in other organizational risk management efforts such as Process Hazards Analyses (PHA) or reliability centered maintenance (RCM). It complements these efforts to provide a more thorough assessment of the risks associated with equipment operations. RBI produces Inspection and Maintenance Plans for equipment that identify the actions that should be implemented to provide reliable and safe operation. The RBI effort can provide input into an organization’s annual planning and budgeting that define the staffing and funds required to maintain equipment operation at acceptable levels of performance and risk.

1.2 SCOPE 1.2. 1.2.1 1 Indu Indust stry ry scop scope e Although the risk management principles and concepts that RBI is built on are universally applicable, RP 580 is specifically targeted at the application of RBI in the hydrocarbon and chemical process industry.

1.2.2 1.2 .2 Flexib Flexibili ility ty in Appli Applicat cation ion Because of the broad diversity in organizations’ size, culture, federal and/or local regulatory requirements, RP 580 offers users the flexibility to apply the RBI methodology within the context of existing corporate risk management practices and to accommodate unique local circumstances. The document is designed to provide a framework that clarifies the expected attributes of a quality risk assessment without imposing undue constraints on users. RP 580 is intended to promote consistency and quality in the identification,


assessment and management of risks pertaining to material deterioration, which could lead to loss of containment. Many types of RBI methods exist and are currently being applied throughout industry. This document is not intended to single out one specific approach as the recommended method for conducting a RBI effort. The document instead is intended to clarify the elements of a RBI analysis.

1.2.3 1.2 .3 Mechan Mechanica icall Inte Integri grity ty Focus Focused ed The RBI process is focused on maintaining the mechanical integrity of pressure equipment items and minimizing the risk of loss of containment due to deterioration. RBI is not a substitute for a process hazards analysis (PHA) or HAZOP. TypiTypically, PHA risk assessments focus on the process unit design and operating practices and their adequacy given the unit’s current or anticipated operating conditions. RBI complements the PHA by focusing on the mechanical integrity related deterioration mechanisms and risk management through inspection. RBI also is complementary to reliability centered maintenance (RCM) programs in that both programs are focused on understanding failure modes, addressing the modes and therefore improving the reliability of equipment and process facilities.

1.2. 1.2.4 4 Equi Equipm pmen entt Cover Covered ed The following types of pressurized equipment and associated components/internals are covered by this document: a. b. c. d. e. f. g.

Pressure Pressure vessels—all vessels—all pressure pressure containing containing components. components. Process Process piping—pipe piping—pipe and piping piping components components.. Storage Storage tanks—atmos tanks—atmospheric pheric and pressurize pressurized. d. Rotating Rotating equipment—press equipment—pressure ure containing containing components. components. Boilers Boilers and heaters—pre heaters—pressuri ssurized zed components. components. Heat exchange exchangers rs (shells, (shells, heads, heads, channels channels and bundles) bundles).. Pressure Pressure relief relief devices. devices.

1.2. 1.2.5 5 Equi Equipm pmen entt Not Not Cover Covered ed The following non-pressurized equipment is not covered by this document: a. Instrument Instrument and control control systems. systems. b. Electr Electrica icall systems. systems. c. Struct Structura urall syste systems. ms. d. Machinery Machinery components components (except (except pump pump and compressor compressor casings).

1.3 1.3 TAR ARGE GET T AUDI AUDIEN ENCE CE The primary audience for RP 580 is inspection and engineering personnel who are responsible for the mechanical integrity and operability of equipment covered by this recommended practice. However, while an organization’s Inspection/Materials Engineering group may champion the RBI initiative, RBI is not exclusively an inspection activity.


RISK-BASED INSPECTION

RBI requires the involvement of various segments of the organization such as engineering, maintenance and operations. Implementation of the resulting RBI product (e.g., inspection plans, replacement/upgrading recommendations, etc.) may rest with more than one segment of the organization. RBI requires the commitment and cooperation of the total organization. In this context, while the primary audience may be inspection and materials engineering personnel, others within the organization who are likely to be involved should be familiar with the concepts and principles embodied in the RBI methodology.

2 References 2.1 2.1

REFE RE FERE RENC NCED ED PUBLI PUBLICA CATI TION ONS S

API API 510

Pressure Vessel Inspection Code—Inspection, Repair, Alteration, and Rerating

API 570

Piping Inspection Code—Inspection, Repair, Alteration Alteration,, and Rerating Rerating of Inservice Piping Systems

RP 579 Std 653

Fitness-For-Service

RP 750 RP 752

RP 941

Tank Inspection, Repair, Alteration, and Reconstructio Reconstruction n Management Management of of Process Process Hazar Hazards ds Management Management of Hazards Hazards Associated Associated With With Location Location of Process Process Plant Plant Buildings, Buildings, CMA Managers Managers Guide Guide Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries Refineries and Petr Petrochem ochemical ical Plants Plants

ACC1 Responsible Responsible Care—CAER Code Resource Resource Guide

AIChE2 Dow’s Dow’s Fire Fire and Explosion Explosion Index Index Hazard Hazard Classification Guide , 1994

A Comparison of Criteria For For Acceptance Acceptance of Risk – PVRC Project 99-IP-01 , Febru-

ary 16, 2000

Chemistry Council, 1300 Wilson Boulevard, Arlington, Virginia, 22209, www.americanchemistry www.americanchemistry.com. .com. 2American Institute of Chemical Engineers, 3 Park Avenue, New York, New York York 10016-5991, www.aiche.org. 3American Society of Mechanical Engineers, 345 East 47th Street, New York, York, New York York 10017, www.asme.org.

Management Plan (40 CFR Part 68) Risk Management (RMP) Regulations

ISO5 Risk Manage Management ment Terminol Terminology ogy

OSHA6 29 CFR 1910.119 Process Safety Management

2.2 2.2 OTHE OTHER R RE REFE FERE RENC NCES ES The following publications are offered as a guide to assist the user in the development of risk-based inspection programs. These references have have been developed specifically for determining risk of process units and equipment, and/or developing risk-based inspection programs for process equipment. In these references, the user will find many more referreferences and examples pertaining to risk assessments of process equipment. Resource ce Document Document on Risk-Ba Risk-Based sed 1. Publ Public icat atiion 581 581 Base Resour Inspection, Inspection, American Petroleum Institute. Risk-Based Inspection Inspection, Applications Handbook, Ameri2. Risk-Based can Society of Mechanical Engineers. 3. Risk-Based Risk-Based Inspection, Inspection, Development of Guidelines, CRTD, Vol. Vol. 20-3, American Society of Mechanical Engineers, 1994. Risk-Based Inspection, Inspection, Development of Guidelines, 4. Risk-Based CRTD, Vol. Vol. 20-2, American Society of Mechanical Engineers, 1992. 5. Guidelines for Quantitative Risk Assessment , Center for Chemical Process Safety, American Institute of Chemical Engineers, 1989. 6. A Collabora Collaborativ tivee Framew Framework ork for for Office Office of Pipeline Pipeline Safety Cost-Benefit Analyses, September 2, 1999. 7. Economic Economic Values for Evaluat Evaluation ion of Federal Federal Aviati Aviation on Administration Investment and Regulatory Programs, FAA-APO-98-8, June 1998. The following references are more general in nature, but provide background development in the field of risk analysis and decision making, while some provide relevant examples. 1.

ASME3

1American

EPA EPA4 58 FR FR 54 54190

3

Pipeline Risk Management Manual, Muhlbauer, W.K.,

Gulf Publishing Company, 2nd Edition, 1996. Engineering Economics and Investment Investment Decision Meth2. Engineering ods, Stermole, F.J., Investment Evaluations Corporation, 1984. 4Environmental

Protection Agency, 1200 Pennsylvania Avenue, N.W., N.W., Washington, District of Columbia 20460, 204 60, www.epa.gov. 5 International Organization for Standardization, 1, rue de Varembe, Case postale 56, CH-1211 Geneve 20, Switzerland, www.iso.ch. 6 Occupational Safety and Health Administration, 200 Constitution Avenue, N.W., Washington, District of Columbia 20210, www.osha.gov.

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4


3. Introducti Introduction on to Decision Analysis Analysis, Skinner, D.C., Probabilistic Publishing, 1994. 4. Center for Process Process Safety, Safety, Americ American an Institut Institutee of Chemical Engineers (AIChE). Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs. New York: York: AIChE, 1994.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

Center for Process Process Safety, Safety, Americ American an Institut Institutee of Chemical Engineers (AIChE). Guidelines for Use of Vapor Cloud Dispersion Models. New York, York, AIChE, 1987. Center for Process Process Safety, Safety, Americ American an Institut Institutee of Chemical Engineers (AIChE). “International Conference and Workshop on Modeling and Mitigating the Consequences of Accidental Releases of Hazardous Materials,” Materials,” September 26-29, 1995. New York: York: AIChE, 1995. Federa Federall Emergen Emergency cy Manage Managemen mentt Agency Agency,, U.S. DepartDepartment of Transportation, U.S. Environmental Protection Handbook of Chemical Chemical Hazard Hazard Analysis Analysis ProceProceAgency. Handbook dures, 1989. Madsen, Madsen, Warren Warren W. and Robert C. Wagner Wagner.. “An Accurate Methodology for Modeling the Characteristics of Explosion Effects.” Process Safety Progress, 13 (July 1994), 171-175. Mercx, W.P.M., .P.M., D.M. Johnson, Johnson, and and J. Puttock. Puttock. “Valida “Valida-tion of Scaling Techniques for Experimental Vapor Cloud Explosion Investigations.” Process Safety Progress, 14 (April 1995), 120. Mercx, W.P W.P.M., .M., R.M.M. van Wees, Wees, and G. Opschoor. “Current Research at TNO on Vapor Cloud Explosion Modeling.” Process Safety Progress Progress, 12 (October 1993), 222. Prugh, Richard Richard W. W. “Quantitati “Quantitative ve Evaluati Evaluation on of Fireball Fireball Hazards.” Process Safety Progress, 13 (April 1994), 8391. Scheuermann, Scheuermann, Klaus Klaus P. P. “Studies “Studies About the the Influence Influence of Turbulence on the Course of Explosions.” Process Safety Progress, 13 (October 1994), 219. TNO Bureau for Industrial Industrial Safety, Safety, Netherlands Netherlands OrganizaOrganization for Applied Scientific Research. Methods for the Calculation of the Physical Effects of the Escape of Dangerous Material (Liquids and Gases). Voorburg, the Netherlands: TNO (Commissioned by Directorate-General of Labour), 1980. TNO Bureau for Industrial Industrial Safety, Safety, Netherlands Netherlands OrganizaOrganization for Applied Scientific Research. Methods for the Determination of Possible Deterioration to People and Objects Resulting from Releases of Hazardous Materials. Rijswijk, the Netherlands: TNO (Commissioned by Directorate-General of Labour), 1992. Touma, Jawad Jawad S., et al. “Performance “Performance Evaluation Evaluation of Journal of Applied Applied Dense Gas Dispersion Models.” Journal Meteorol Meteorology ogy, 34 (March 1995), 603-615. U.S. Environmenta Environmentall Protection Agency Agency,, Federal Emergency Management Agency, U.S. Department of Transportation. Technical Guidance for Hazards Analy-


sis, Emergency Planning for Extremely Hazardous Substances. December 1987.

17. U.S. Environment Environmental al Protection Protection Agency Agency, Office of Air Quality Planning and Standards. Workbook of Screening Techniques for Assessing A ssessing Impacts of Toxic Air Pollutants. EPA-450/4-88-009. EPA-450/4-88-009. September 1988. 18. U.S. Environment Environmental al Protection Protection Agency Agency, Office of Air Quality Planning and Standards. Guidance on the Application of Refined Dispersion Models for Hazardous/ Toxic Air Release. EPA-454/R-93-002. May 1993.

19. U.S. Environment Environmental al Protection Protection Agency Agency, Office of Pollution Prevention and Toxic Substances. Flammable Gases and Liquids and Their Hazards. EPA EPA 744-R-94-002. February 1994.

3 3.1 3.1

Defin De finit itio ions ns and and Ac Acro ron nyms yms DEFIN EFINIT ITIO ION NS

For purposes of this recommended practice, the following definitions shall apply.

3.1. 3.1.1 1 abso absolu lute te risk risk:: An ideal and accurate description and quantification of risk. 3.1.2 ALARP 3.1.2 ALARP (As (As Low As As Reason Reasonabl ably y Practic Practical) al):: A concept of minimization that postulates that attributes (such as risk) can only be reduced to a certain minimum under current technology and with reasonable cost. 3.1. 3.1.3 3 cons conseq eque uenc nce: e: Outcome from an event. There may be one or more consequences from an event. Consequences may range from positive to negative. However, consequences are always negative for safety aspects. Consequences may be expressed qualitatively or quantitatively. quantitatively. 3.1. 3.1.4 4 dama damage ge tole tolera ranc nce: e: The amount of deterioration that a component can withstand without failing. 3.1. 3.1.5 5 dete deteri rior orat atio ion: n: The reduction in the ability of a component to provide its intended purpose of containment of fluids. This can be caused by various deterioration mechanisms (e.g., thinning, cracking, mechanical). Damage or degradation may be used in place of deterioration. 3.1.6 event: Occurrence of a particular set of circumstances. The event may be certain or uncertain. The event can be singular or multiple. The probability associated with the event can be estimated for a given period of time. 3.1. 3.1.7 7 event vent tree tree:: An analytical tool that organizes and characterizes potential accidents in a logical and graphical manner. The event tree begins with the identification of potential initiating events. Subsequent possible events (including activation of safety functions) resulting from the initiating events are then displayed as the second level of the event tree. This process is continued to develop pathways or scenarios from the initiating events to potential outcomes.


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3.1. 3.1.8 8 exte extern rnal al eve event nt:: Events resulting from forces of nature, acts of God or sabotage, or such events as neighboring fires or explosions, neighboring hazardous material releases, electrical power failures, tornadoes, earthquakes, and intrusions of external transportation vehicles, such as aircraft, ships, trains, trucks, or automobiles. External events are usually beyond the direct or indirect control of persons employed at or by the facility. 3.1.9 failure: Termination of the ability of a system, structure, or component to perform its required function of containment of fluid (i.e., loss of containment). Failures may be unannounced and undetected until the next inspection (unannounced failure), or they may be announced and detected by any number of methods at the instance of occurrence (announced failure). 3.1. 3.1.10 10 fail failur ure e mode mode:: The manner of failure. For riskbased inspection, the failure of concern is loss of containment of pressurized equipment items. Examples of failure modes are small hole, crack, and rupture. 3.1.11 haza azard: A physical condition or a release of a hazardous material that could result from component failure and result in human injury or death, loss or damage, or environmental degradation. Hazard is the source of harm. Components that are used to transport, store, or process a hazardous material can be a source of hazard. Human error and external events may also create a hazard. 3.1.12 Hazard 3.1.12 Hazard and and Opera Operabil bility ity (HAZO (HAZOP) P) Study Study:: A HAZOP study is a form of failure modes and effects analysis. HAZOP studies, which were originally developed for the process industry, use systematic techniques to identify hazards and operability issues throughout an entire facility. facility. It is particularly useful in identifying unforeseen hazards designed into facilities due to lack of information, or introduced into existing facilities due to changes in process conditions or operating procedures. The basic objectives of the techniques are:

5

to a long-run relative frequency of occurrence or to a degree of belief that an event will occur. For a high degree of belief, the probability is near one. Frequency rather than probability may be used in describing risk. Degrees of belief about probability can be chosen as classes or ranks like “Rare/unlikely/ moderate/likely/almost certain” or “incredible/improbable/ remote/ occasional/probable/frequent”.

3.1.16 Quali 3.1.16 Qualitat tative ive Risk Risk Analysi Analysis s (Assessm (Assessment ent): ): Methods that use engineering judgment and experience as the bases for the analysis of probabilities and consequences of failure. The results of qualitative risk analyses are dependent on the background and expertise of the analysts and the objectives of the analysis. Failure Modes, Effects, and Criticality Analysis (FMECA) and HAZOPs are examples of qualitative risk analysis techniques that become quantitative risk analysis methods when consequence and failure probability values are estimated along with the respective descriptive input. 3.1.17 Quant 3.1.17 Quantita itativ tive e Risk Analysi Analysis s (Assessm (Assessment ent): ): An analysis that: a. Identifies Identifies and delineates delineates the combinati combinations ons of events events that, if they occur, will lead to a severe accident (e.g., major explosion) or any other undesired event. b. Estimates Estimates the frequen frequency cy of occurrence occurrence for for each combination. c. Estima Estimates tes the consequ consequenc ences. es.

3.1. 3.1.14 14 miti mitiga gati tion on:: Limitation of any negative consequence or reduction in probability of a particular event.

Quantitative risk analysis integrates into a uniform methodology the relevant information about facility design, operating practices, operating history, component reliability, human actions, the physical progression of accidents, and potential environmental and health effects, usually in as realistic a manner as possible. Quantitative risk analysis uses logic models depicting combinations of events that could result in severe accidents and physical models depicting the progression of accidents and the transport of a hazardous material to the environment. The models are evaluated probabilistically to provide both qualitative and quantitative insights about the level of risk and to identify the design, site, or operational characteristics that are the most important to risk. Quantitative risk analysis logic models generally consist of event trees and fault trees. Event trees delineate initiating events and combinations of system successes and failures, while fault trees depict ways in which the system failures represented in the event trees can occur. These models are analyzed to estimate the frequency of each accident sequence.

3.1. 3.1.15 15 prob probab abil ilit ity: y: Extent to which an event is likely to occur within the time frame under consideration. The mathematical definition of probability is “a real number in the scale 0 to 1 attached to a random event”. Probability can be related

3.1. 3.1.18 18 rela relati tive ve risk risk:: The comparative risk of a facility, process unit, system, equipment item or component to other facilities, process units, systems, equipment items or components, respectively. respectively.

a. To produce a full descrip description tion of the facilit facility y or process, process, including the intended design conditions. b. To systematically review review every every part of the facility facility or process to discover how deviations from the intention of the design can occur. c. To decide whether whether these these deviations deviations can lead lead to hazards or operability issues. d. To assess effectiv effectiveness eness of safeguards. safeguards.

3.1. 3.1.13 13 like likeli liho hood od:: Probability.



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3.1. 3.1.19 19 resi residu dual al risk risk:: The risk remaining after risk mitigation. 3.1.20 risk: Combination of the probability of an event and its consequence. In some situations, risk is a deviation from the expected. When probability and consequence are expressed numerically, risk is the product. 3.1. 3.1.21 21 risk risk ac acce cept ptan ance ce:: A decision to accept a risk. Risk acceptance depends on risk criteria. 3.1. 3.1.22 22 risk risk anal analys ysis is:: Systematic use of information to identify sources and to estimate the risk. Risk analysis provides a basis for risk evaluation, risk mitigation and risk acceptance. Information can include historical data, theoretical analysis, informed opinions and concerns of stakeholders.

3.1. 3.1.32 32 risk risk mana manage geme ment nt:: Coordinated activities to direct and control an organization with regard to risk. Risk management typically includes risk assessment, risk mitigation, risk acceptance and risk communication. 3.1. 3.1.33 33 risk risk miti mitiga gati tion on:: Process of selection and implementation of measures to modify risk. The term risk mitigation is sometimes used for measures themselves. 3.1. 3.1.34 34 risk risk red reduc ucti tion on:: Actions taken to lessen the probability, negative consequences, or both associated with a particular risk. 3.1.35 source: ce: Thing or activity with a potential for consequence. Source in a safety context is a hazard.

3.1. 3.1.23 23 risk risk a ass sses essm smen ent: t: Overall process of risk analysis and risk evaluation.

3.1. 3.1.36 36 sour source ce ident identifi ifica cati tion on:: Process to find, list, and characterize sources. In the safety area, source identification is called hazard identification.

3.1. 3.1.24 24 risk risk avoi avoida danc nce: e: Decision not to become involved in, or action to withdraw from a risk situation. The decision may be taken based on the result of risk evaluation.

3.1. 3.1.37 37 stak stakeh ehol olde der: r: Any individual, group or organization that may affect, be affected by, or perceive itself to be affected by the risk.

3.1. 3.1.25 25 riskrisk-ba based sed insp inspect ectio ion: n: A risk assessment and management process that is focused on loss of containment of pressurized equipment in processing facilities, due to material deterioration. These risks are managed primarily through equipment inspection.

3.1. 3.1.38 38 toxi toxic c chem chemic ical al:: Any chemical that presents a physical or health hazard or an environmental hazard according to the appropriate Material Safety Data Sheet. These chemicals (when ingested, inhaled or absorbed through the skin) can cause damage to living tissue, impairment of the central nervous system, severe illness, or in extreme cases, death. These chemicals may also result in adverse effects to the environment (measured as ecotoxicity and related to persistence and bioaccumulation potential).

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3.1. 3.1.26 26 risk risk com commu muni nica cati tion on:: Exchange or sharing of information about risk between the decision maker and other stakeholders. The information may relate to the existence, nature, form, probability, severity, severity, acceptability, mitigation or other aspects of risk. 3.1. 3.1.27 27 risk risk cont contro rol: l: Actions implementing risk management decisions. Risk control may involve monitoring, reevaluation, acceptance and compliance with decisions. 3.1. 3.1.28 28 risk risk crit criter eria ia:: Terms of reference by which the significance of risk is assessed. Risk criteria may include associated cost and benefits, legal and statutory requirements, socio-economic and environmental aspects, concerns of stakeholders, priorities and other inputs to the assessment. 3.1. 3.1.29 29 risk risk esti estima mati tion on:: Process used to assign values to the probability and consequence of a risk. Risk estimation may consider cost, benefits, stakeholder concerns and other variables, as appropriate for risk evaluation. 3.1. 3.1.30 30 risk risk eval evalua uati tion on:: Process used to compare the estimated risk against given risk criteria to determine the significance of the risk. Risk evaluation may be used to assist in the acceptance or mitigation decision. 3.1. 3.1.31 31 risk risk iden identi tific ficati ation on:: Process to find, list, and characterize elements of risk. Elements may include; source, event, consequence, probability. Risk identification may also identify stakeholder concerns.


3.1. 3.1.39 39 unmi unmiti tiga gate ted d risk: risk: The risk prior to mitigation activities. 3.2

ACRONYMS

ACC AIC AIChE ALARP ANSI API ASME ASNT AST ASTM BLEVE CCPS COF EPA FAR FMEA HAZO HAZOP P

American Chemistry Council Ame American Inst nstitute of Chemical Engi nginee neers As Low As Reasonably Practical American Na National Standards In Institute American Petroleum Institute American Society of Mechanical Engineers American So Society of of No Nondestructive Testing Ame American Society of Testing and Materials Boiling Li Liquid Ex Expanding Vapor Explosion Center fo for Ch Chemical Pr Process Sa Safety Consequence of Failure Environmental Protection Agency Fatality Accident Rate Failure Mo Modes an and Ef Effects Analysis Haz Hazard and Ope Operability Ass Assessment



ISO

International Organization for Standardization Management of Change National Association of of Co Corrosion Engineers Non destructive examination National Fi Fire Pr Protection As Association Occupational Safety and Health Administration Process Hazards Analysis Positive Material Identification Probability of Failure Process Safety Management Pressure Vessel Research Council Quality As Assurance/Quality Co Control Quantitative Risk Assessment Risk-Based Inspection Reliability Centered Maintenance Risk Management Plan Tubular Exchangers Manufacturers Association The Netherlands Or Organization fo for Applied Scientific Research

MOC NACE NDE NFPA OSHA PHA PMI POF PSM PVRC QA/QC QRA RBI RCM RMP TEMA TNO

4 Basic Concepts 4.1 4.1 WHAT IS RISK? ISK? Risk is something that we as individuals live with on a dayto-day basis. Knowingly or unknowingly, unknowingly, people are constantly making decisions based on risk. Simple decisions such as driving to work or walking across a busy street involve risk. More important decisions such as buying a house, investing money and getting married all imply an acceptance of risk. Life is not risk-free and even even the most cautious, risk-adverse individuals inherently take risks. For example, in driving a car, people accept the probability that they could be killed or seriously seriously injured. The reason this risk is accepted is that people consider the probability of being killed or seriously injured to be sufficiently low as to make the risk acceptable. Influencing the decision are the the type of car, the safety features installed, traffic volume and speed, and other factors such as the availability, risks and affordability of other alternatives (e.g., mass transit). Risk is the combination of the probability of some event occurring during a time period of interest and the consequences, (generally negative) associated with the event. In mathematical terms, risk can be calculated by the equation: Risk = Probability x Consequence Likelihood is sometimes used as a synonym for probability, however probability is used throughout this document for consistency.

4.2 RISK RISK MANA MANAGEM GEMENT ENT AND RISK RISK REDUC REDUCTIO TION N At first, it may seem that risk management and risk reduction are synonymous. However, risk reduction is only part of risk management. Risk reduction is the act of mitigating a known risk to a lower level of risk. Risk management is a process to assess risks, to determine if risk reduction is required and to develop a plan to maintain risks at an acceptable level. By using risk management, some risks may be identified as acceptable so that no risk reduction (mitigation) is required.

4.3 THE EVOLU EVOLUTIO TION N OF INSPECT INSPECTION ION INTER INTERVA VALS LS In process plants, inspection and testing programs are established to detect and evaluate deterioration due to in-service operation. The effectiveness effectiveness of inspection programs varvaries widely, ranging from reactive programs, which concentrate on known areas of concern, to broad proactive programs covering a variety of equipment. One extreme of this would be the “don’t fix it unless it’s broken” approach. The other extreme would be complete inspection of all equipment items on a frequent basis. Setting the intervals between inspections has evolved over time. With the need to periodically verify equipment integrity, organizations initially resorted to time-based or “calendarbased” intervals. With advances in inspection approaches, and better understanding of the type and rate of deterioration, inspection intervals became more dependent on the equipment condition, rather than what might have been an arbitrary calendar date. Codes and standards such as API 510, 570 and 653 evolved to an inspection philosophy with elements such as: a. Inspection Inspection interval intervalss based on some percentag percentagee of equipment life (such as half life). b. On-stream On-stream inspection inspection in lieu of internal internal inspection inspection based on low deterioration rates. c. Internal Internal inspection inspection requirement requirementss for deterioration deterioration mechamechanisms related to process environment induced cracking. d. Consequence Consequence based based inspection inspection interva intervals. ls. RBI represents the next generation of inspection approaches and interval setting, recognizing that the ultimate goal of inspection is the safety and reliability of operating facilities. RBI, as a risk-based approach, focuses attention specifically on the equipment and associated deterioration mechanisms representing the most risk to the facility. facility. In focusing on risks and their mitigation, RBI provides a better linkage between the mechanisms that lead to equipment failure and the inspection approaches that will effectively reduce the associated risks. In this document, failure is loss of containment.

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7


8

4.4 4.4


INSP INSPEC ECTI TION ON OPTIM OPTIMIZ IZAT ATIO ION N

When the risk associated with individual equipment items is determined and the relative effectiveness of different inspection techniques in reducing risk is estimated or quantified, adequate information is available for developing an optimization tool for planning and implementing a risk-based inspection program. Figure 1 presents stylized curves showing the reduction in risk that can be expected when the degree and frequency of inspection are increased. The upper curve in Figure 1 represents a typical inspection program. Where there is no inspection, there may be a higher level of risk, as indicated on the yaxis in the figure. With an initial investment investment in inspection activities, risk generally is significantly reduced. A point is reached where additional inspection activity begins to show a diminishing return and, eventually, may produce very little additional risk reduction. If excessive inspection is applied, the level of risk may even go up. This is because invasive inspections in certain cases may cause additional deterioration (e.g., moisture ingress in equipment with polythionic acid; inspection damage to protective coatings or glass lined vessels). This situation is represented by the dotted line at the end of the upper curve. RBI provides a consistent methodology for assessing the optimum combination of methods and frequencies. Each available inspection method can be analyzed and its relative effectiveness in reducing failure probability estimated. Given this information and the cost of each procedure, an optimization program can be developed. The key to developing such a procedure is the ability to assess the risk associated with each item of equipment and then to determine the most appropriate inspection techniques for that piece of equipment. A conceptual result of this methodology is illustrated by the lower curve in Figure 1. The lower curve indicates that with the application of an effective RBI program, lower risks can be achieved with the same level of inspection activity. This is because, through RBI, inspection activities are focused on higher risk items and away from lower risk items. As shown in Figure 1, risk cannot be reduced to zero solely by inspection efforts. The residual risk factors for loss of containment include, but are not limited to, the following: a. Huma Human n erro errorr. b. Natura Naturall disast disasters ers.. c. External External events events (e.g., collisions collisions or falling falling objects) objects).. d. Secondary Secondary effects effects from from nearby nearby units. units. e. Consequentia Consequentiall effects effects from associate associated d equipment equipment in the same unit. f. Delibe Deliberat ratee acts (e.g., (e.g., sabota sabotage) ge).. g. Fundamental Fundamental limitati limitations ons of inspection inspection method. method. h. Desi Design gn erro errors rs.. i. Unknown Unknown mechanisms mechanisms of deteriorati deterioration. on.

Many of these factors are strongly influenced by the process safety management system in place at the facility.

4.5 RELATI RELATIVE VE RISK RISK VS. ABS ABSOLU OLUTE TE RISK RISK The complexity of risk calculations is a function of the number of factors that can affect the risk. Calculating absolute risk can be very time and cost consuming and often, due to having too many uncertainties, is impossible. Many variables are involved with loss of containment in hydrocarbon and chemical facilities and the determination of absolute risk numbers is often not cost effective. RBI is focused on a systematic determination of relative risks. In this way, facilities, units, systems, equipment or components can be ranked based on relative risk. This serves to focus the risk management efforts on the higher ranked risks. It is considered, however, that if a Quantitative RBI study is conducted rigorously that the resultant risk number is a fair approximation of the actual risk of loss of containment due to deterioration. Numeric risk values determined in qualitative and semi-quantitative assessments using appropriate sensitivity analysis methods also may be used to evaluate risk acceptance.

5 Intr Introd oduc uctio tion n to Risk Risk-Ba -Based sed Inspe Inspecti ction on 5.1 CONSEQ CONSEQUEN UENCE CE AND AND PROBA PROBABIL BILITY ITY FOR FOR RISK-BASED INSPECTION The objective of RBI is to determine what incident could occur (consequence) in the event of an equipment failure, and how likely (probability) is it that the incident could happen. For example, if a pressure vessel subject to deterioration from corrosion under insulation develops a leak, a variety of consequences could occur. Some of the possible consequences are:

Risk with typical inspection programs k s i R

Risk using RBI and an optimized inspection program

Residual risk not affected by RBI

Level of inspection activity

Figure 1—Management 1—Management of Risk Risk Using Using RBI

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a. Form a vapor vapor cloud that that could ignite ignite causing causing injury injury and equipment damage. b. Release Release of a toxic chemical chemical that that could cause cause health health problems. c. Result in a spill spill and cause environm environmental ental deteriora deterioration. tion. d. Force a unit unit shutdown shutdown and have have an adverse economi economicc impact. e. Have minimal minimal safety safety, health, environmen environmental tal and/or economic impact. Combining the probability of one or more of these events with its consequences will determine the risk to the operation. Some failures may occur relatively frequently without significant adverse safety, environmental or economic impacts. Similarly, some failures have potentially serious consequences, but if the probability of the incident is low, then the risk may not warrant immediate action. However, However, if the probability and consequence combination (risk) is high enough to be unacceptable, then a mitigation action to predict or prevent the event is recommended. Traditionally, organizations have focused solely on the consequences of failure or on the probability without systematic efforts tying the two together. They have not considered how likely itit is that an undesirable incident will occur. occur. Only by considering both factors can effective risk-based decision making take place. Typically, risk acceptability criteria are defined, recognizing that not every failure will lead to an undesirable incident with serious consequence (e.g., water leaks) and that some serious consequence incidents have very low probabilities. Understanding the two-dimensional aspect of risk allows new insight into the use of risk for inspection prioritization and planning. Figure 2 displays the risk associated with the operation of a number of equipment items in a process plant. Both the probability and consequence of failure have been determined for ten equipment items, and the results have been plotted. The points represent the risk associated with each equipment item. item. Ordering by risk produces a risk-based ranking of the equipment items to be inspected. From this list, an inspection plan can be developed that focuses attention on the areas of highest risk. An “iso-risk” line is shown on Figure 2. This line represents a constant risk level. A user defined acceptable risk level could be plotted as an iso-risk line. In this way the acceptable risk line would separate the unacceptable from the acceptable risk items. Often a risk plot is drawn using log-log scales for a better understanding of the relative risks of the items assessed.

9

ISO-risk line 2

1

e r u l i a f f o y t i l i b a b o r P

6 5 7 4 9 10

8

3

Consequence of failure

Figur Figure e 2— 2—Ris Risk k Plot Plot a. b. c. d. e. f.

Object Objectiv ivee of the study study.. Number of facilit facilities ies and equipment equipment items items to study. study. Availa vailable ble resource resources. s. Study Study time time frame. frame. Complexity Complexity of facili facilities ties and and processes. processes. Nature and quality quality of availab available le data. data.

The RBI procedure can be applied qualitatively, quantitatively or by using aspects of both (i.e., semi-quantitatively). Each approach provides a systematic way to screen for risk, identify areas of potential concern, and develop a prioritized list for more in depth inspection or analysis. Each develops a risk ranking measure to be used for evaluating separately the probability of failure and the potential consequence of failure. These two values are then combined to estimate risk. Use of expert opinion will typically be included in most risk assessments regardless of type or level.

5.2. 5.2.1 1 Qual Qualit itat ativ ive e Appr Approa oach ch This approach requires data inputs based on descriptive information using engineering judgment and experience as the basis for the analysis of probability and consequence of failure. Inputs are often given in data ranges instead of discrete values. Results are typically given in qualitative terms such as high, medium and low, although numerical values may be associated with these categories. The value of this type of analysis is that it enables completion of a risk assessment in the absence of detailed quantitative data. The accuracy of results from a qualitative analysis is dependent on the background and expertise of the analysts.

5.2 5.2 TYPES YPES OF OF RBI RBI AS ASSE SESS SSME MENT NT

5.2. 5.2.2 2 Quan Quanti tita tati tive ve Appro Approac ach h

Various types of RBI assessment may be conducted at several levels. The choice of approach is dependent on multiple variables such as:

Quantitative risk analysis integrates into a uniform methodology the relevant information about facility design, operating practices, operating history, component reliability,

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10


High

Detail of RBI analysis Low

Qualitative RBI

Semi-qualitative RBI

Quantitative RBI

Figure 3—Continuum 3—Continuum of RBI Approach Approaches es human actions, the physical progression of accidents, and potential environmental and health effects. Quantitative risk analysis uses logic models depicting combinations of events that could result in severe accidents and physical models depicting the progression of accidents and the transport of a hazardous material to the environment. The models are evaluated probabilistically to provide both qualitative and quantitative insights about the level of risk and to identify the design, site, or operational characteristics that are the most important to risk. Quantitative risk analysis is distinguished from the qualitative approach by the analysis depth and integration of detailed assessments. Quantitative risk analysis logic models generally consist of event trees and fault trees. Event trees delineate initiating events and combinations of system successes and failures, while fault trees depict ways in which the system failures represented in the event trees can occur. These models are analyzed to estimate the probability of each accident sequence. Results using this approach are typically presented as risk numbers (e.g., cost per year).

5.2.3 5.2 .3 Semi-q Semi-quan uantit titati ative ve Appro Approach ach Semi-quantitative is a term that describes any approach that has aspects derived from both the qualitative and quantitative approaches. It is geared to obtain the major benefits of the previous two approaches (e.g., speed of the qualitative and rigor of the quantitative). Typically, Typically, most of the data used in a quantitative approach is needed for this approach but in less detail. The models also may not be as rigorous as those used for the quantitative approach. The results are usually given in consequence and probability categories rather than as risk numbers but numerical values may be associated with each category to permit the calculation of risk and the application of appropriate risk acceptance criteria.

5.2. 5.2.4 4 Cont Contin inuu uum m of Appro Approac ache hes s In practice, a RBI study typically uses aspects of qualitative, quantitative and semi-quantitative approaches. These RBI approaches are not considered as competing but rather as complementary. For example, a high level qualitative approach could be used at a unit level to find the unit within a

facility that provides the highest risk. Systems and equipment within the unit then may be screened using a qualitative approach with a more quantitative approach used for the higher risk items. Another example could be to use a qualitative consequence analysis combined with a semi-quantitative probability analysis. The three approaches are considered to be a continuum with qualitative and quantitative approaches being the extremes of the continuum and everything in between being a semi-quantitative approach. Figure 3 illustrates this continuum concept. The RBI process, shown in the simplified block diagram in Figure 4, depicts the essential elements of inspection planning based on risk analysis. This diagram is applicable to Figure 3 regardless which RBI approach is applied, i.e., each of the essential elements shown in Figure in Figure 4 are are necessary for a complete RBI program regardless of approach (qualitative, semi-quantitative or quantitative).

5.2.5 5.2 .5 Quanti Quantitat tative ive R Risk isk A Asse ssessme ssment nt (QRA (QRA)) Quantitative Risk Assessment (QRA) refers to a prescriptive methodology that has resulted from the application of risk analysis techniques at many different types of facilities, including hydrocarbon and chemical process facilities. For all intents and purposes, it is a traditional risk analysis. A RBI analysis shares many of the techniques and data requirements with a QRA. If a QRA has been prepared for a process unit, the RBI consequence analysis can borrow extensively from this effort. The traditional QRA is generally comprised of five tasks: a. b. c. d. e.

System Systemss identific identificati ation. on. Hazards Hazards identific identificati ation. on. Probab Probabili ility ty assessme assessment. nt. Consequ Consequenc encee analysis. analysis. Risk Risk res resul ults ts..

The systems definition, hazard identification and consequence analysis are integrally linked. Hazard identification in a RBI analysis generally focuses on identifiable failure mechanisms in the equipment (inspectable causes) but does not explicitly deal with other potential failure scenarios resulting from events such as power failures or human errors. A QRA

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deals with total risk, not just risk associated with equipment deterioration. The QRA typically involves a much more detailed evaluation than a RBI analysis. The following data are typically analyzed: a. Existing Existing HAZOP or process process hazards hazards analysis analysis (PHA) (PHA) results. b. Dike Dike and draina drainage ge design design.. c. Hazard Hazard detect detection ion syste systems. ms. d. Fire protection protection systems. systems. e. Releas Releasee stati statisti stics. cs. f. Inju Injury ry stati statist stic ics. s. g. Population Population distribut distributions. ions. h. Topograp opography hy.. i. Weather eather conditi conditions ons.. j. Land use. use. Experienced risk analysts generally perform a QRA. There are opportunities to link the detailed QRA with a RBI study.

5.3 5.3

PREC PR ECIS ISIO ION N VS VS.. ACC ACCUR URAC ACY Y

Risk presented as a precise numeric value (as in a quantitative analysis) implies a greater level of accuracy when compared to a risk matrix (as in a qualitative analysis). The implied linkage of precision and accuracy may not exist because of the element of uncertainty that is inherent with probabilities and consequences. The accuracy of the output is a function of the methodology used as well as the quantity and quality of the data available. The basis for predicted damage and rates, the level of confidence in inspection data and the technique used to perform the inspection are all factors that should be considered. In practice, there are often many many extraneous factors that will affect the estimate of damage rate (probability) as well as the magnitude of a failure (conse-

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quence) that cannot be fully taken into account with a fixed model. Therefore, it may be beneficial to use quantitative and qualitative methods in a complementary fashion to produce the most effective and efficient assessment. Quantitative analysis uses logic models to calculate probabilities and consequences of failure. Logic models used to characterize materials deterioration of equipment and to determine the consequence of failures typically can have significant variability and therefore could introduce error and inaccuracy impacting the quality of the risk assessment. Therefore, it is important that results from these logic models are validated by expert judgment. The accuracy of any type of RBI analysis depends on using a sound methodology, methodology, quality data and knowledgeable personnel.

5.4 UNDER UNDERST STAND ANDING ING HOW HOW RBI RBI CAN CAN HELP HELP TO TO MANAGE OPERATING RISKS The mechanical integrity and functional performance of equipment depends on the suitability of the equipment to operate safely and reliably under the normal and abnormal (upset) operating conditions to which the equipment is exposed. In performing performing a RBI assessment, the susceptibility susceptibility of equipment to deterioration by one or more mechanisms (e.g., corrosion, fatigue and cracking) is established. The susceptibility of each equipment item should be clearly defined for the current operating conditions including such factors as: a. Process Process fluid, contaminants contaminants and aggressi aggressive ve components. components. b. Unit Unit throug throughput hput.. c. Desired Desired unit run length length between between scheduled scheduled shutdowns. shutdowns. d. Operating Operating conditions, conditions, including including upset upset conditions: conditions: e.g., pressures, temperatures, flow rates, pressure and/or temperature cycling.

Risk assessment process

Consequence of failure Data and information collection

Risk ranking

Inspection plan

Mitigation (if any)

Probability of failure

Reassessment

Figure 4—Risk-based 4—Risk-based Inspection Inspection Planning Process



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The suitability and current condition of the equipment within the current operating envelope will determine the probability of failure (POF) of the equipment from one or more deterioration deterioration mechanisms. mechanisms. This probability, probability, when coupled with the associated consequence of failure (COF) (see Section 11) will determine the operating risk associated with the equipment item, and therefore the need for mitigation, if any, such as inspection, metallurgy change or change in operating conditions.

5.5 5.5

MANA MA NAGE GEME MENT NT OF RISK RISKS S

5.5.1 5.5 .1 Ris Risk k Managem Management ent Throug Through h Inspect Inspection ion Inspection influences the uncertainty of the risk associated with pressure equipment primarily by improving knowledge of the deterioration state and predictability of the probability of failure. Although inspection does not reduce risk directly, it is a risk management activity that may lead to risk reduction. In-service inspection is primarily concerned with the detection and monitoring of deterioration. The probability of failure due to such deterioration is a function of four factors: a. Deterioratio Deterioration n type type and and mechanism mechanism.. b. Rate Rate of deterio deteriorat ration ion.. c. Probability Probability of identifyin identifying g and detecting deteriora deterioration tion and predicting future deterioration states with inspection technique(s). d. Tolerance olerance of the equipment equipment to the type of deteriorat deterioration. ion.

5.5.2 5.5 .2 Using Using RBI RBI to Establ Establish ish Inspe Inspecti ction on Plans Plans and and Priorities The primary product of a RBI effort should be an inspection plan for each equipment item evaluated. evaluated. The inspection plan should detail the unmitigated risk related to the current operation. For risks considered unacceptable, the plan should contain the mitigation actions that are recommended to reduce the unmitigated risk to acceptable levels. For those equipment items where inspection is a costeffective means of risk management, the plans should describe the type, scope and timing of inspection/examination recommended. Ranking of the equipment by the unmitigated risk level allows users to assign priorities to the various inspection/examination tasks. The level level of the unmitigated risk should be used to evaluate the urgency for performing the inspection.

5.5. 5.5.3 3 Othe Otherr Ris Risk k Man Manag agem emen entt It is recognized that some risks cannot be adequately managed by inspection alone. Examples where inspection may not be sufficient to manage risks to acceptable levels are: a. Equipment Equipment nearing nearing retirem retirement. ent.

b. Failure Failure mechanisms mechanisms (such as brittle brittle fracture, fracture, fatigue) fatigue) where avoidance of failure primarily depends on operating within a defined pressure/temperature envelope. c. Consequence-d Consequence-domina ominated ted risks. risks. In such cases, non-inspection mitigation actions (such as equipment repair, replacement or upgrade, equipment redesign or maintenance of strict controls on operating conditions) may be the only appropriate measures that can be taken to reduce risk to acceptable levels. Refer to Section 13 for methods of risk mitigation other than inspection.

5.6 RELATI RELATIONS ONSHIP HIP BETW BETWEEN EEN RBI RBI AND AND OTHER OTHER RISK-BASED AND SAFETY INITIATIVES The risk-based inspection methodology is intended to complement other risk-based risk-based and safety initiatives. The output from several of these initiatives can provide input to the RBI effort, and RBI outputs may be used to improve safety and risk-based initiatives already implemented by organizations. Examples of some initiatives are: a. b. c. d. e. f. g. h.

OSHA psm progra programs. ms. EPA EPA risk management management program programs. s. ACC ACC respon responsib sible le care. care. ASME risk risk assessmen assessmentt publicatio publications. ns. CCPS risk risk assessment assessment techniques. techniques. Reliability Reliability centered centered maintenance. maintenance. Process Process hazards hazards analysis. analysis. Seveso Seveso 2 directi directive ve in Europe. Europe.

The relationship between RBI and several initiatives is described in the following examples:

5.6. 5.6.1 1 Proc Process ess H Haza azard rds s Analy Analysi sis s A process hazards analysis (PHA) uses a systemized approach to identify and analyze hazards in a process unit. The RBI study can include a review of the output from any PHA that has been conducted on the unit being evaluated. Hazards identified in the PHA can be specifically addressed in the RBI analysis. Potential hazards identified in a PHA will often affect the probability of failure side of the risk equation. The hazard may result from a series of events that could cause a process upset, or it could be the result of process design or instrumentation deficiencies. In either case, the hazard may increase the probability of failure, in which case the RBI procedure should reflect the same. Some hazards identified would affect the consequence side of the risk equation. For example, the potential failure of an isolation valve could increase the inventory of material available for release in the event of a leak. The consequence calculation in the RBI procedure can be modified to reflect this added hazard.

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Likewise, the results of a RBI assessment can significantly enhance the overall value of a PHA.

5.6. 5.6.2 2 Proc Process ess Safe Safety ty Mana Manage geme ment nt A strong process safety management system can significantly reduce risk levels in a process plant (refer to OSHA 29 CFR 1910.119 or API RP 750). RBI may include methodologies to assess the effectiveness of the management systems in maintaining mechanical integrity. The results of such a management systems evaluation are factored into the risk determinations. Several of the features of a good PSM program provide input for a RBI study. Extensive data on the equipment and the process are required in the RBI analysis, and output from PHA and incident investigation reports increases the validity of the study. In turn, the RBI program can improve the mechanical integrity aspect of the PSM program. An effective effective PSM program includes a well-structured equipment inspection program. The RBI system will improve the focus of the inspection plan, resulting in a strengthened PSM program. Operating with a comprehensive inspection program should reduce the risks of releases from a facility and should provide benefits in complying with safety-related initiatives.

5.6. 5.6.3 3 Equi Equipm pmen entt Reliab Reliabil ilit ity y Equipment reliability programs can provide input to the probability analysis portion of a RBI program. Specifically, reliability records can be used to develop equipment failure probabilities and leak frequencies. Equipment reliability is especially important if leaks can be caused by secondary failures, such as loss of utilities. Reliability efforts, such as reliability centered maintenance (RCM), can be linked with RBI, resulting in an integrated program to reduce downtime in an operating unit.

5.7 RELATI RELATIONS ONSHIP HIP WITH WITH JURI JURISDI SDICT CTION IONAL AL REQUIREMENTS Codes and legal requirements vary from one jurisdiction to another. In some cases, jurisdictional requirements mandate specific actions such as the type of inspections and intervals between inspections. In jurisdictions that permit the application of the API inspection codes and standards, RBI should be an acceptable method for setting inspection plans. It is recommended that all users review their jurisdictional code and legal requirements for acceptability of using RBI for inspection planning purposes.

6 Plan Planni ning ng the the RBI RBI As Asse sess ssme ment nt 6.1 6.1 GETT GETTIN ING G STAR STARTE TED D This section helps a user determine the scope and the priorities for a RBI assessment. Screening is done to focus the

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effort. Boundary limits are identified to determine what is vital to include in the assessment. The organizing process of aligning priorities, screening risks, and identifying boundaries improves the efficiency and effectiveness of conducting the assessment and its end-results in managing risk. A RBI assessment is is a team-based process. At the beginning of the exercise, it is important to define: a. Why the the assessme assessment nt is being done. b. How the the RBI assessment assessment will be carried carried out. c. What knowled knowledge ge and skills skills are requir required ed for the assessment. d. Who is on the RBI team team.. e. What are are their their roles roles in the the RBI process process.. f. Who is responsi responsible ble and accounta accountable ble for what what actions. actions. g. Which facilit facilities, ies, assets, assets, and components components will be included. included. h. What data data is to be be used in the the assessment assessment.. i. What codes and standa standards rds are are applica applicable. ble. j. When the the assessmen assessmentt will be completed completed.. k. How long the assessme assessment nt will remain remain in effect effect and when it will be updated. l. How How the result resultss will will be used used..

6.2 ESTABL ESTABLISH ISHING ING OBJE OBJECTI CTIVES VES AND AND GOALS GOALS OF OF A RBI ASSESSMENT A RBI assessment should be undertaken with clear objectives and goals that are fully understood by all members of the RBI team and by management. Some examples are listed in 6.2.1 to 6.2.7.

6.2. 6.2.1 1 Unde Underrstan stand d Risk Risks s An objective of the RBI assessment may be to better understand the risks involved in the operation of a plant or process unit and to understand the effects that inspection, maintenance and mitigation actions have on the risks. From the understanding of risks, an inspection program may be designed that optimizes the use of inspection and plant maintenance resources.

6.2. 6.2.2 2

Defin Define e Risk Risk Crit Criter eria ia

A RBI assessment will determine the risk associated with the items assessed. The RBI team and management may wish to judge whether the individual equipment item and cumulative risks risks are acceptable. Establishing risk criteri criteriaa to judge acceptability acceptability of risk could be an objective objective of the RBI assessment if such criteria do not exist already within the user’s company.

6.2. 6.2.3 3

Mana Ma nage geme ment nt of Risks Risks

When the risks are identified, inspection actions and/or other mitigation that have a positive effect in reducing risk to an acceptable level may may be undertaken. These actions may be --`,,``,,`,,,,,,`,,,`,,````,`,-`-`,,`,,`,`,,`---



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significantly different from the inspection actions undertaken during a statutory or certification type inspection program. The results of managing and reducing risk are improved safety, avoided losses of containment, and avoided commercial losses.

6.2. 6.2.4 4

Red Re duce uce C Cos osts ts

Reducing inspection costs is usually not the primary objective of a RBI assessment, but it is frequently a side effect of optimization. When the inspection program is optimized based on an understanding of risk, one or more of the following cost reduction benefits may be realized. a. Ineffecti Ineffective, ve, unnecessary unnecessary or inappropriat inappropriatee inspection activiactivities may be eliminated. b. Inspection Inspection of low low risk items may may be eliminated eliminated or reduced. reduced. c. On-line On-line or non-invasi non-invasive ve inspection inspection methods methods may be substituted for invasive methods that require equipment shutdown. d. More effecti effective ve infrequent infrequent inspections inspections may be substituted substituted for less effective frequent inspections.

6.2.5 Meet Safety Safety and Enviro Environmen nmental tal Management Management Requirements Managing risks by using RBI assessment can be useful in implementing an effective inspection program that meets performance-based safety and environmental requirements. RBI focuses efforts on areas where the the greatest risk exists. RBI provides a systematic method to guide a user in the selection of equipment items to be included and the frequency, scope and extent of inspection activities to be conducted to meet performance objectives.

6.2.6 6.2 .6 Sort Sort Mitiga Mitigatio tion n Altern Alternati atives ves The RBI assessment may identify risks that may be managed by actions other than inspection. Some of these mitigation actions may include but are not limited to: a. Modification Modification of the process process to eliminate eliminate conditio conditions ns driving driving the risk. b. Modification Modification of operating operating procedures procedures to avoid situation situationss driving the risk. c. Chemical Chemical treatment treatment of the process process to reduce deterioratio deterioration n rates/susceptibilities. d. Change metallur metallurgy gy of components components to reduce POF. POF. e. Removal Removal of unnecessary unnecessary insulation insulation to reduce probabili probability ty of corrosion under insulation. f. Reduce inventori inventories es to reduce COF. COF. g. Upgrade Upgrade safety safety or detectio detection n systems. systems. h. Change fluids fluids to less less flammable flammable or toxic toxic fluids. fluids. The data within the RBI assessment can be useful in determining the optimum economic strategy to reduce risk. The strategy may be different at different times in a plant’s life cycle. For example, it is usually more economical to modify


the process or change metallurgy when a plant is being designed than when it is operating.

6.2.7 6.2 .7 New New Pro Projec jectt Risk Risk Ass Assessm essment ent A RBI assessment made on new equipment or a new project, while in the design stage, may yield important information on potential risks. This may allow the risks to be minimized by design, prior to actual installation.

6.2.8 6.2 .8 Facil Faciliti ities es End End of Life Life Strat Strategi egies es Facilities approaching the end of their economic or operating service life are a special case where application of RBI can be very useful. The end of life case for plant operation operation is about gaining the maximum remaining economic benefit from an asset without undue personnel, environmental or financial risk. End of life strategies focus the inspection efforts directly on high-risk areas where the inspections will provide a reduction of risk during the remaining life of the plant. Inspection activities that do not impact risk during the remaining life are usually eliminated or reduced. End of life inspection RBI strategies may be developed in association with a fitness for service assessment of damaged components using methods described in API RP 579. It is important to revisit the RBI assessment if the remaining plant life is extended after the remaining life strategy has been developed and implemented.

6.3 6.3

INIT INITIA IAL L SCRE SCREEN ENIN ING G

6.3.1 6.3 .1 Establ Establish ish Phy Physica sicall Bounda Boundarie ries s of a RBI Assessment Boundaries for physical assets included in the assessment are established consistent with the overall objectives. The level of data to be reviewed and the resources available to accomplish the objectives directly impact the extent of physical assets that can be assessed. The screening process is important in centering the focus on the most important physical assets so that time and resources are effectively applied. The scope of a RBI assessment may vary between an entire refinery or plant and a single component within a single piece of equipment. Typically, RBI is done on multiple pieces of equipment (e.g., an entire process unit) rather than on a single component.

6.3. 6.3.2 2 Faci Facili liti ties es Scre Screen enin ing g At the facility level, RBI may be applied to all types of plants including but not limited to: a. b. c. d.

Oil and and gas production production facili facilities. ties. Oil and gas processing processing and transport transportation ation terminal terminals. s. Refin Refiner erie ies. s. Petrochemic Petrochemical al and chemic chemical al plants. plants.


` , , ` , ` , , ` , , ` ` , ` , ` ` ` ` , , ` , , , ` , , , , , , ` , , ` ` , , ` -


e. Pipelines Pipelines and pipelin pipelinee stations stations.. f. LNG LNG plan plants ts.. Screening at the facility level may be done by a simplified qualitative RBI assessment. Screening at the facility level could also be done by: a. b. c. d. e. f.

Asset Asset or prod product uct valu value. e. History History of problems/failu problems/failures res at each facility facility.. PSM/no PSM/non-P n-PSM SM faciliti facilities. es. Age of of facil faciliti ities. es. Proxim Proximity ity to to the publi public. c. Proximity Proximity to environm environmentall entally y sensitive sensitive areas. areas.

Examples of key questions to answer at the facility level are: 1. Is the facility facility located located in a regulatory regulatory jurisdiction jurisdiction that will accept modifications to statutory inspection intervals based on RBI? 2. Is the management management of the facility facility willing willing to invest invest in the resources necessary to achieve the benefits of RBI? 3. Does the facility facility have have sufficient sufficient resources resources and experexpertise available to conduct the RBI assessment?

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6.3.4 6.3 .4 System Systems s within within Pro Process cess Unit Units s Screeni Screening ng It is often advantageous to group equipment within a process unit into systems or circuits where common environmental operating conditions exist based on process chemistry, pressure and temperature, metallurgy, equipment design and operating history. history. By dividing a process unit into systems, the equipment can be screened together saving time compared to treating each piece of equipment separately. A common practice utilizes block flow or process flow diagrams for the unit to identify the systems. Information about metallurgy, process conditions, credible deterioration mechanisms and historical problems may be identified on the diagram for each system. When a process unit is identified for a RBI assessment and overall optimization is the goal, it is usually best to include all systems within the unit. Practical considerations such as resource availability may require that the RBI assessment is limited to one or more systems within the unit. Selection of systems may be based on: a. b. c. d.

Relative Relative risk of the the systems. systems. Relati Relative ve COF of syste systems. ms. Relative Relative reliabilit reliability y of system systems. s. Expected Expected benefit benefit from applyin applying g RBI to a system. system.

6.3. 6.3.3 3 Proc Process ess Uni Units ts Scre Screen enin ing g If the scope of the RBI assessment is a multi-unit facility, then the first step in the application of RBI is screening of entire process units to rank relative relative risk. The screening points out areas that are higher in priority and suggests which process units to begin with. It also provides provides insight about the the level of assessment that may be required for operating systems and equipment items in the various units. Priorities may be assigned based on one of the following: a. b. c. d. e. f.

Relative Relative risk risk of the the process process units. units. Relative Relative economic economic impact of the process process units. units. Relative Relative COF COF of the the process process units. Relative Relative reliabili reliability ty of the process process units. units. Turna Turnarou round nd schedu schedule. le. Experience Experience with similar similar process process units.

Examples of key questions to answer at the process unit level are similar to the questions at the facility level: 1. Does the process process unit unit have a significan significantt impact on the the operation of the facility? 2. Are there significan significantt risks involv involved ed in the operation operation of the process unit and would the effect of risk reduction be measurable? 3. Do process process unit operators operators see see that some some benefit may may be gained through the application of RBI? 4. Does the process process unit have have sufficient sufficient resources resources and expertise available to conduct the RBI assessment?

6.3.5 6.3 .5 Equipm Equipment ent Items Items Screen Screening ing In most plants, a large percentage of the total unit risk will be concentrated in a relatively small percentage of the equipment items. These potential high-risk items should receive receive greater attention in the risk assessment. assessment. Screening of equipment items is often conducted to identify the higher risk items to carry forward to more detailed risk assessment. A RBI assessment may be applied to all pressure containing equipment such as: a. b. c. d. e. f. g. h. i. j.

Pipi Piping ng.. Pressu Pressure re vess vessels els.. Reac Reacto tors rs.. Heat Heat excha exchange ngers. rs. Furn Furnac aces es.. Tanks. Pumps (pressure (pressure boundary). boundary). Compressors Compressors (pressure (pressure boundar boundary). y). Pressu Pressure re relief relief devic devices. es. Control Control valves valves (pressur (pressuree boundary). boundary).

Selection of equipment types to be included is based on meeting the objectives objectives discussed in 6.2. The following issues may be considered in screening the equipment to be included: 1. Will Will the integrity integrity of safeguard safeguard equipment equipment be comprocompromised by deterioration mechanisms? 2. Which types types of equipment equipment have have had the most reliabi reliability lity problems?

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3. Which pieces pieces of equipment equipment have have the highest highest COF if there is a pressure boundary failure? 4. Which pieces pieces of equipment equipment are are subject to to most deteriodeterioration that could affect pressure boundary containment? 5. Which pieces pieces of equipment equipment have have lower lower design safety safety margins and/or lower corrosion allowances that may affect pressure boundary containment considerations?

than normal conditions. A good example is polythionic acid stress corrosion cracking. The POF for susceptible plants is controlled by whether mitigation measures are applied during shutdown procedures. Start-up lines are often included within the process piping and their service conditions during start-up and subsequent operation should be considered.

6.4.2 6.4 .2 Normal Normal,, Upse Upsett and Cyc Cyclic lic Oper Operati ation on 6.3.6 6.3 .6 Utilit Utilities ies,, Emerge Emergency ncy and and Off-plo Off-plott Systems Systems Whether or not utilities, emergency and off-plot systems should be included depends on the planned use of the RBI assessment and the current inspection requirements of the facility. Possible reasons for inclusion of off-plot and utilities are: a. The RBI assessment assessment is being being done for an overall overall optimiza optimiza-tion of inspection resources and environmental and business COF are included. b. There is a specific reliabili reliability ty problem in a utility utility system. system. An example would be a cooling water system with corrosion and fouling problems. A RBI approach could assist in developing the most effective combination of inspection, mitigation, monitoring, and treatment for the entire facility. c. Reliability Reliability of the process process unit is a major major objective objective of the RBI analysis. When emergency systems (e.g., flare systems, emergency shutdown systems) are included in the RBI assessment, their service conditions during both routine operations and their duty cycle should be considered.

6.4 ESTAB ESTABLIS LISH H OPERA OPERATIN TING G BOUND BOUNDARI ARIES ES Similar to physical boundaries, operating boundaries for the RBI study are established consistent with the study objectives, level of data to be reviewed and resources. The purpose of establishing operational boundaries is to identify key process parameters that may impact deterioration. The RBI assessment normally includes review of both POF and COF for normal operating conditions. Start-up and shut-down shut-down conditions conditions as well as emergency and non-routine conditions should also be reviewed for their potential effect on POF and COF. The operating conditions, including any sensitivity analysis, used for the RBI assessment should be recorded as the operating limits for the assessment. Operating within the boundaries is critical to the validity of the RBI study as well as good operating practice. It may be worthwhile to monitor key process parameters to determine whether operations are maintained within boundaries.

The normal operating conditions may be most easily provided if there is a process flow model or mass balance available for the plant or process unit. However, the normal operating conditions found on documentation should be verified as it is not uncommon to find discrepancies that could impact the RBI results substantially. The following data should be provided: a. Operating Operating temperature temperature and pressure pressure including including variati variation on ranges. b. Process Process fluid composition composition including including variation variation with feed composition ranges. c. Flow rates rates includin including g variation variation ranges. ranges. d. Presence Presence of moisture moisture or other contaminant contaminant species. species. Changes in the process, such as pressure, temperature or fluid composition, resulting from unit abnormal or upset conditions should be considered in the RBI assessment. Systems with cyclic operation, such as reactor regeneration systems, should consider the complete cyclic range of conditions. Cyclic conditions could impact the probability of failure due to some deterioration mechanisms (e.g., fatigue, thermal fatigue, corrosion under insulation).

6.4. 6.4.3 3 Oper Operat atin ing g Tim Time e Perio Period d The unit run lengths of the selected process units/equipment is an important limit to consider. consider. The RBI assessment may include the entire operational life, or may be for a selected period. For example, process units are occasionally shut down for maintenance activities and the associated run length may depend on the condition of the equipment in the unit. A RBI analysis may focus on the current run period or may include the current and next-projected next-projected run period. The time period may also influence the types of decisions and inspection plans that result from the study, such as inspection, repair, replace, operating, and so on. Future operational pro jections jections are also important important as part of the basis for the operational time period.

6.5 SELECT SELECTING ING A TYPE OF OF RBI ASSES ASSESSME SMENT NT

6.4. 6.4.1 1 Start Start-u -up p and and Shut Shut-d -dow own n

Selection of the type of RBI assessment will be dependent on a variety of factors, such as:

Process conditions during start-up and shut-down can have a significant effect on the risk of a plant especially when they are more severe (likely to cause accelerated deterioration)

a. Is the assessment assessment at a facility facility,, process unit, unit, system, equipequipment item or component level. b. Objective Objective of the the assessmen assessment. t.



` , , ` , ` , , ` , , ` ` , ` , ` ` ` ` , , ` , , , ` , , , , , , ` , , ` ` , , ` -


c. d. e. f.

Availabili vailability ty and quality quality of data. Resource Resource availabi availability lity.. Perceived Perceived or previousl previously y evaluated evaluated risks. risks. Time Time const constra rain ints ts..

A strategy should be developed, matching the type of assessment to the expected or evaluated risk. For example, processing units that are expected to have lower risk may only require simple, fairly conservative methods to adequately accomplish the RBI objectives. Whereas, process units which have a higher expected risk may require more detailed methods. Another example would be to evaluate all equipment items in a process unit qualitatively and then evaluate the higher risk items identified more quantitatively. Refer to 5.2 for more on types of RBI assessment.

6.6 ESTIMA ESTIMATIN TING G RESOUR RESOURCES CES AND AND TIME TIME REQUIRED The resources and time required to implement a RBI assessment will vary widely between organizations depending on a number of factors including: a. Implementat Implementation ion strategy/p strategy/plans. lans. b. Knowledge Knowledge and training training of implem implementers enters.. c. Availabili vailability ty and quality of necessary necessary data and information. information. d. Availabili vailability ty and cost of resources resources needed needed for implementation. e. Amount of of equipment equipment included included in each each level level of RBI analysis. f. Degree Degree of complexi complexity ty of RBI RBI analysis analysis selected selected.. g. Degree Degree of accuracy accuracy required. required. The estimate of scope and cost involved in completing a RBI assessment might include the following: 1. Number of facili facilities, ties, units, units, equipment equipment items, items, and components to be evaluated. 2. Time Time and resources resources required required to gather gather data for the items to be evaluated. 3. Training Training time time for for implement implementers. ers. 4. Time Time and resources resources required required for RBI assessme assessment nt of data and information. 5. Time Time and resources to evaluat evaluatee RBI assessment assessment results and develop inspection, maintenance, and mitigation plans.

7 Data Data and and Info Informa rmatio tion n Colle Collecti ction on for for RBI RBI Assessment 7.1 7.1

RBII DA RB DATA TA NE NEED EDS S

A RBI study may use a qualitative, semi-quantitative and/ or quantitative approach. The fundamental difference among these approaches is the amount and detail of input, calculations and output.

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For each RBI approach it is important to document all bases for the study and assumptions from the onset and to apply a consistent rationale. Any deviations from from prescribed, standard procedures should be well documented. Documentation of unique equipment and piping identifiers is a good starting point for any level of study. The equipment should also correspond to a unique group or location such as a particular process unit at a particular plant site. Typical data needed for a RBI analysis may include but is not limited to: a. Type of of equipm equipment ent.. b. Materials Materials of constructio construction. n. c. Inspection, Inspection, repair repair and replace replacement ment records. records. d. Process Process fluid composition compositions. s. e. Inven Inventor tory y of fluid fluids. s. f. Operat Operating ing conditi conditions ons.. g. Safety Safety system systems. s. h. Detect Detection ion syst systems ems.. i. Deterioratio Deterioration n mechanisms, mechanisms, rates rates and and severity severity.. j. Personnel Personnel densitie densities. s. k. Coating, Coating, cladding cladding and and insulation insulation data. data. l. Busine Business ss inte interru rrupti ption on cost. cost. m. Equipment replacement costs. n. Environme Environmental ntal remediati remediation on costs. costs.

7.1. 7.1.1 1 Qual Qualit itat ativ ive eR RBI BI The qualitative approach typically does not require all of the data mentioned in 7.1. Further, items required only need to be categorized into broad ranges or classified versus a reference point. It is important to establish a set of rules to assure consistency in categorization or classification. Generally, a qualitative analysis using broad ranges requires a higher level of judgment, skill and understanding from the user than a quantitative approach. Ranges and summary fields may evaluate circumstances with widely varying conditions requiring the user to carefully consider the impact of input on risk results. Therefore, despite its simplicity, it is important to have knowledgeable and skilled persons perform the qualitative RBI analysis.

7.1. 7.1.2 2 Quan Quanti tita tati tive ve RBI RBI Quantitative risk analysis uses logic models depicting combinations of events that could result in severe accidents and physical models depicting the progression of accidents and the transport of a hazardous material to the environment. The models are evaluated probabilistically to provide both qualitative and quantitative insights about the level of risk and to identify the design, site, or operational characteristics that are the most important to risk. Hence, more detailed information and data are needed for quantitative RBI in order to provide input for the models. --`,,``,,`,,,,,,`,,,`,,````,`,-`-`,,`,,`,`,,`---



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7.1. 7.1.3 3 Semi Semi-q -qua uant ntit itat ativ ive e RBI RBI The semi-quantitative analysis typically requires the same data as a quantitative analysis but generally not as detailed. For example, the fluid volumes may be estimated. Although the precision of the analysis may be less, the time required for data gathering and analysis will be less too.

7.2 7.2

DATA DA TA QUA UALI LITY TY

The data quality has a direct relation to the relative accuracy of the RBI analysis. Although the data requirements are quite different for the various types of RBI analysis, quality of input data is equally important. It is beneficial to the integrity of a RBI analysis to assure that the data are up to date and validated by knowledgeable persons (see Section 15). As is true in any inspection program, data validation is essential for a number of reasons. Among the reasons are outdated drawings and documentation, inspector error, clerical error, and measurement equipment accuracy. Another potential source of error in the analysis is assumptions on equipment history. For example if baseline inspections were not performed or documented, nominal thickness may be used for the original thickness. This assumption can significantly impact the calculated corrosion rate early in the equipment’s life. The effect may be to mask a high corrosion rate or to inflate a low corrosion rate. A similar situation exists when the remaining life of a piece of equipment with a low corrosion rate requires inspection more frequently. The measurement error may result in the calculated corrosion rate appearing artificially high or low. This validation step stresses the need for a knowledgeable individual comparing data from the inspections to the expected deterioration deterioration mechanism and rates. This person may also compare the results with previous measurements on that system, similar systems at the site or within the company or published data. Statistics may be useful in this review. This review should also factor in any changes or upsets in the process. ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

7.3 CODES CODES AND AND STANDA STANDARD RDS— S—NAT NATION IONAL AL AND AND INTERNATIONAL In the data collection stage, an assessment of what codes and standards are currently in use, or were in use during the equipment design, is generally necessary. The amount and type of codes and standards used by a facility can have a significant impact on RBI results.

7.4 SOURC SOURCES ES OF SITE SITE SPECI SPECIFIC FIC DATA DATA AND AND INFORMATION Information for RBI can be found in many places within a facility. facility. It is important to stress stress that the precision of the data should match the complexity complexity of the RBI method used. The individual or team should understand the sensitivity of the data needed for the program before gathering any data. It may


be advantageous to combine RBI data gathering with other risk/hazard analysis data gathering (e.g., PHA, QRA) as much of the data overlaps. Specific potential sources of information include but are not limited to: a. Design and and Constructio Construction n Records/Dra Records/Drawings. wings. 1. P&IDs, P&IDs, PFDs PFDs,, MFDs, MFDs, etc. etc. 2. Piping isometric isometric drawings. drawings. 3. Engineering Engineering specificatio specification n sheets. sheets. 4. Materials Materials of of constructi construction on records. records. 5. Construction Construction QA/QC records. records. 6. Codes Codes and stand standard ardss used. used. 7. Protectiv Protectivee instrumen instrumentt systems. systems. 8. Leak detectio detection n and monitorin monitoring g systems. systems. 9. Isolat Isolation ion syst systems ems.. 10. Inven Inventor tory y records. records. 11. Emergency Emergency depressur depressurizing izing and relief relief systems. systems. 12. Safety Safety system systems. s. 13. Fire-proofing Fire-proofing and fire fighting systems. systems. 14. 14. Layo Layout ut.. b. Inspec Inspectio tion n Records Records.. 1. 2. 3. 4. 5.

Schedules Schedules and frequency frequency.. Amount and types types of of inspectio inspection. n. Repair Repairss and alterati alterations ons.. PMI PMI rec recor ords ds.. Inspec Inspectio tion n results results..

c. Proc Proces esss Dat Data. a. 1. Fluid compositi composition on analysis analysis including including contaminants contaminants or trace components. 2. Distributed Distributed control control system system data. data. 3. Operat Operating ing proced procedure ures. s. 4. Start-up Start-up and shut-down shut-down procedur procedures. es. 5. Emerg Emergenc ency y proced procedure ures. s. 6. Operating Operating logs logs and process process records. records. 7. PSM, PHA, PHA, RCM and QRA data or or reports. reports. d. Management Management of of change change (MOC) records. records. e. Off-Site Off-Site data and information information—if —if consequence consequence may affect affect off-site areas. f. Fail Failur uree data data.. 1. 2. 3. 4. 5.

Generic Generic failure frequency frequency data—indu data—industry stry or in-house. in-house. Industry Industry specific specific failure failure data. data. Plant and and equipment equipment specific specific failure failure data. Reliability Reliability and and condition condition monitoring monitoring records. records. Leak Leak dat data. a.

g. Site Site cond conditi itions ons.. 1. Climate/wea Climate/weather ther records. records. 2. Seismic Seismic activity activity records. records. h. Equipment Equipment replacement replacement costs.



1. Projec Projectt cost cost report reports. s. 2. Indust Industry ry datab database ases. s. i. Haza Hazard rdss dat data. a. 1. PSM PSM stu studi dies es.. 2. PHA studi studies es.. 3. QRA stud studie ies. s. 4. Other site site specific specific risk or hazard studies studies.. j. Incident Incident investi investigatio gations. ns.

8 Ident Identify ifying ing Det Deteri eriora oratio tion n Mecha Mechanis nisms ms and Failure Modes 8.1 8.1

INT INTRODUC ODUCTI TION ON

Identification of the appropriate deterioration mechanisms, susceptibilities and failure modes for all equipment included in a RBI study is essential to the quality and the effectiveness of the RBI evaluation. A metallurgist or corrosion specialist should be consulted to define the equipment deterioration mechanisms, susceptibility and potential failure modes. Data used and assumptions made should be validated and documented. Process conditions (normal and upset) as well as anticipated process changes should be considered in the evaluation. The deterioration mechanisms, rates and susceptibilities are the primary inputs into the probability of failure evaluation. The failure mode is a key input in determining the consequence of failure except when a worst case consequence analysis, assuming total release of component inventory, is used.

8.2 FAILU FAILURE RE AND AND FAILU FAILURE RE MODES MODES FOR FOR RISKRISKBASED INSPECTION The term failure can be defined as termination of the ability to perform a required function. RBI, as described in this Recommended Practice, is concerned with one type of failure, namely loss of containment caused by deterioration. The term failure mode is defined as the manner of failure. Failure modes can range from a small hole to a complete rupture.

8.3 DETERI DETERIORA ORATIO TION N MECHAN MECHANISM ISMS S The term deterioration mechanism is defined as the type of deterioration that could lead to a loss of containment. There are four major deterioration mechanisms observed in the hydrocarbon and chemical process industry: a. b. c. d.

Thinning Thinning (includes (includes internal internal and external external). ). Stress corrosion corrosion cracking. cracking. Metallurgi Metallurgical cal and and environm environmental. ental. Mech Mechan anic ical al..

Understanding equipment operation and the interaction with the chemical and mechanical environment is key to performing deterioration mechanism identification. For example,


19

understanding that localized thinning may be caused by the method of fluid injection and agitation is as important as knowing the corrosion mechanism. Process specialists can provide useful input (such as the spectrum of process conditions, injection points etc.) to aid materials specialists in the identification of deterioration mechanisms and rates. Appendix A provides tables describing the individual deterioration mechanisms covered by these four categories, the key variables driving deterioration, and typical process industry examples of where they may occur. These tables cover most of the common deterioration mechanisms. Other deterioration types and mechanisms may occur in specific hydrocarbon and chemical processing applications; however, these are relatively infrequent.

8.3.1 Thinning Thinning includes general corrosion, localized corrosion, pitting, and other mechanisms that cause loss of material from internal or external surfaces. surfaces. The effects of thinning can be determined from the following information: a. Thickness Thickness – both the the original, original, historic historic and current current meameasured thickness. b. Equipment Equipment age – number number of years in the current current service service and if the service has changed. c. Corrosion Corrosion allowance allowance – design design allowance allowance for the current current service. d. Corros Corrosion ion rate. rate. e. Operating Operating pressur pressuree and temperatur temperature. e. f. Desi Design gn pre press ssur ure. e. g. Number and types types of inspections. inspections.

8.3.2 8.3 .2 Stress Stress Corro Corrosio sion n Cracki Cracking ng Stress corrosion cracking (SCC) occurs when equipment is exposed to environments conducive to certain cracking mechanisms such as caustic cracking, amine cracking, sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), stress-oriented hydrogen-induced cracking (SOHIC), carbonate cracking, polythionic acid cracking (PTA), and chloride cracking (ClSCC). Literature, expert opinion and experience experience are often necessary to establish susceptibility of equipment to stress corrosion cracking. Susceptibility is often designated as high, medium, or low based on: a. Materi Material al of construc constructio tion. n. b. Mechanism Mechanism and and susceptibi susceptibility lity.. c. Operating Operating tempera temperature ture and pressur pressure. e. d. Concentrati Concentration on of key process process corrosive corrosivess such as pH, chlorides, sulfides, etc. e. Fabrication Fabrication variabl variables es such as post weld heat treatme treatment. nt. The determination of susceptibility should not only consider susceptibility of the equipment/piping to cracking (or


` , , ` , ` , , ` , , ` ` , ` , ` ` ` ` , , ` , , , ` , , , , , , ` , , ` ` , , ` -

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probability of initiating a crack), but also the probability of a crack resulting in a leak or rupture.

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8.3.3 8.3 .3 Metall Metallur urgic gical al and En Environ vironmen mental tal Deterioration of Properties

The probability analysis in a RBI program is performed to estimate the probability of a specific adverse consequence resulting from a loss of containment that occurs due to a deterioration mechanism(s). The probability that that a specific specific consequence will occur is the product of the probability of failure (POF) and the probability of the scenario under consideration assuming that the failure failure has occurred. This section provides guidance only on determining the POF. POF. Guidance on determining the probability of specific consequences is provided in Section 11. The probability of failure analysis should address all deterioration mechanisms to which the equipment being studied is susceptible. Further, it should address the situation where equipment is susceptible to multiple deterioration mechanisms (e.g., thinning and creep). The analysis should be credible, repeatable and well documented. It should be noted that deterioration mechanisms are not the only causes of loss of containment. Other causes of loss of containment could include but are not limited to:

Causes of metallurgical and environmental failure are varied but typically involve some form of mechanical and/or physical property deterioration of the material due to exposure to the process environment. One example of this is high-temperature hydrogen attack (HTHA). HTHA occurs in carbon and low alloy steels exposed to high partial pressures of hydrogen at elevated temperatures. Historically, Historically, HTHA resistance has been predicted based on industry experience that has been plotted on a series of curves for carbon and low alloy steels showing the temperature and hydrogen partial pressure regime in which these steels have been successfully used without deterioration due to HTHA. These curves, which are are commonly referred to as the Nelson curves, are maintained based on industry experience in API RP 941. Consideration for equipment susceptibility to HTHA is based on: ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

a. b. c. d.

Materi Material al of construc constructio tion. n. Operat Operating ing temperat temperature ure.. Hydrog Hydrogen en partial partial pressu pressure. re. Expo Exposu sure re time time..

Refer to Appendix A for other examples of these types of failures and causes. In general, the critical variables for deterioration are material of construction, process operating, startup and shut-down conditions (especially temperature) and knowledge of the deterioration caused by those conditions.

8.3. 8.3.4 4

Mech Me chan aniical cal

Similar to the metallurgical and environmental failures, various types and causes of mechanical deterioration are possible. Examples and the types of failure resulting can be found in the Appendix A. The most common mechanical deterioration mechanisms are fatigue (mechanical, thermal and corrosion), stress/creep rupture, and tensile overload.

8.4 8.4 OTHE OTHER R FAILU AILURE RES S RBI could be expanded to include failures other than loss of containment. Examples of other failures and failure modes are: a. Pressure Pressure relief relief device device failure failure – plugging, plugging, fouling, fouling, nonactivation. b. Heat exchanger exchanger bundle bundle failure failure – tube leak, plugging. plugging. c. Pump failure failure – seal failure failure,, motor failure, failure, rotating rotating parts damage. d. Internal Internal linings linings – hole, disbond disbondment. ment.


Assess Ass essing ing Proba Probabil bility ity of Failu Failure re

9.1 INTRO INTRODUC DUCTIO TION N TO PROBABI PROBABILIT LITY Y ANALYSI ANALYSIS S

a. b. c. d. e. f. g.

Seismi Seismicc activit activity y. Weather eather extrem extremes. es. Overpressure Overpressure due to pressure pressure relief relief device device failure. failure. Operato Operatorr error error.. Inadvertent Inadvertent substitut substitution ion of materials materials of construction. construction. Desig Design n erro errorr. Sabo Sabota tage ge..

These and other causes of loss of containment may have an impact on the probability of failure and may be included in the probability of failure analysis.

9.2 UNITS UNITS OF MEAS MEASURE URE IN IN THE PRO PROBAB BABILI ILITY TY OF FAILURE ANALYSIS Probability of failure is typically expressed in terms of frequency. Frequency is expressed as a number of events occurring during a specific time frame. For probability analysis, the time frame is typically expressed as a fixed interval (e.g., one year) and the frequency is expressed as events per interval (e.g., 0.0002 failures per year). The time frame may also be expressed as an occasion (e.g., one run length) and the frequency would be events per occasion (e.g., 0.03 failures per run). For a qualitative qualitative analysis, the probability of failure may be categorized (e.g., high, medium and low, or 1 through 5). However, even in this case, it is appropriate to associate an event frequency with each probability category to provide guidance to the individuals who are responsible for determining the probability. If this is done, the change from one category to the next could be one or more orders of magnitude or other appropriate demarcations that will provide adequate discrimination.



9.3 TYPES YPES OF PRO PROBAB BABILI ILITY TY ANAL ANALYSI YSIS S The following paragraphs discuss different approaches to the determination of probability. probability. For the purposes of the discussion, these approaches have been categorized as “qualitative” or “quantitative.” However, it should be recognized that “qualitative” and “quantitative” are the end p oints of a continuum rather than distinctive approaches (see Figure 3). 3). Most probability assessments use a blend of qualitative and quantitative approaches. The methodology used for the assessment should be structured such that a sensitivity analysis or other approach may be used to assure that realistic, though conservative, probability values are obtained (see 11.4).

9.3.1 Qualitative Qualitative Probabil Probability ity of Failure Failure Analysis Analysis A qualitative method involves identification of the units, systems or equipment, the materials of construction and the corrosive components of the processes. On the basis of knowledge of the operating history, future inspection and maintenance plans and possible materials deterioration, probability of failure can be assessed separately for each unit, system, equipment grouping or individual equipment item. Engineering judgment is the basis for this assessment. A probability of failure category can then be assigned for each unit, system, grouping or equipment item. Depending on the methodology employed, the categories may be described with words (such as high, medium or low) or may have numerical descriptors (such as 0.1 to 0.01 times per year).

9.3.2 Quantitati Quantitative ve Prob Probabili ability ty of of Failur Failure e Analysi Analysis s There are several approaches to a quantitative probability analysis. One example is to take a probabilistic approach where specific failure data or expert solicitations are used to calculate a probability of failure. These failure data may be obtained on the specific equipment item in question or on similar equipment items. This probability may be expressed as a distribution rather than a single deterministic value. Another approach is used when inaccurate or insufficient failure data exists on the specific item of interest. In this case, general industry, company or manufacturer failure data are used. A methodology should be applied to assess the applicability of these general data. As appropriate, these failure data should be adjusted and made specific to the equipment being analyzed by increasing or decreasing the predicted failure frequencies based on equipment specific information. In this way, general failure data are used to generate an adjusted failure frequency that is applied to equipment for a specific sp ecific application. Such modifications to general values may be made made for each equipment item to account for the potential deterioration that may occur in the particular service and the type and effectiveness of inspection and/or monitoring performed.

Knowledgeable personnel should make these modifications on a case-by-case basis.

9.4 DETERM DETERMINA INATIO TION N OF PRO PROBAB BABILI ILITY TY OF OF FAILURE Regardless of whether a more qualitative or a quantitative analysis is used, the probability of failure is determined by two main considerations: a. Deterioratio Deterioration n mechanisms mechanisms and rates rates of the the equipment equipment item's material of construction, resulting from its operating environment (internal and external). b. Effecti Effectivenes venesss of the inspection inspection program to identify identify and monitor the deterioration mechanisms so that the equipment can be repaired or replaced prior to failure. Analyzing the effect of in-service deterioration and inspection on the probability of failure involves the following steps: a. Identify Identify active active and credible credible deterioration deterioration mechanism mechanismss that are reasonably expected to occur during the time period being considered (considering normal and upset conditions). b. Determine Determine the deterioratio deterioration n susceptibility susceptibility and rate. rate. c. Quantify Quantify the effectiv effectiveness eness of the past inspecti inspection on and maintenance program and a proposed future inspection and maintenance program. It is usually necessary to evaluate the probability of failure considering several alternative future inspection and maintenance strategies, possibly including a “no inspection or maintenance” strategy. d. Determine Determine the probability probability that with the current current condition, condition, continued deterioration at the predicted/expected rate will exceed the damage tolerance of the equipment and result in a failure. The failure mode (e.g., small leak, large leak, equipment rupture) should also be determined based on the deterioration mechanism. It may be desirable in some cases to determine the probability of more than one failure mode and combine the risks.

9.4.1 Determine Determine the Deteriorati Deterioration on Susceptib Susceptibility ility and Rate Combinations of process conditions and materials of construction for each equipment item should be evaluated to identify active and credible deterioration mechanisms. One method of determining these mechanisms and susceptibility is to group components that have the same material of construction and are exposed to the same internal and external environment. Inspection results from one item in the group can be related to the other equipment in the group. For many deterioration mechanisms, the rate of deterioration progression is generally understood and can be estimated for process plant equipment. Deterioration rate can be expressed in terms of corrosion rate for thinning or susceptibility for mechanisms where the deterioration rate is unknown or immeasurable (such as stress corrosion crack-

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21


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ing). Susceptibility is often designated as high, medium or low based on the environmental conditions and material of construction combination. Fabrication variables and repair history are also important. The deterioration rate in specific process equipment is often not known with certainty. certainty. The ability to state the rate of deterioration precisely is affected by equipment complexity, type of deterioration mechanism, process and metallurgical variations, inaccessibility for inspection, limitations of inspection and test methods and the inspector’s expertise. Sources of deterioration rate information include: a. b. c. d. e.

Publ Publis ishe hed d data. data. Labora Laborator tory y testin testing. g. In-situ In-situ testing testing and in-serv in-service ice monitori monitoring. ng. Experience Experience with with similar similar equipme equipment. nt. Previo Previous us inspect inspection ion data. data.

The best information will come from operating experiences where the conditions that led to the observed deterioration rate could realistically be expected to occur in the equipment under consideration. consideration. Other sources of information could include databases of plant experience or reliance on expert opinion. The latter method method is often used since plant databases, where they exist, sometimes do not contain sufficiently detailed information.

have been identified, the inspection program should be evaluated to determine the effectiveness in finding the identified mechanisms. Limitations in the effectiveness of an inspection program could be due to: a. Lack of coverage coverage of an area area subject subject to deterioratio deterioration. n. b. Inherent Inherent limitations limitations of some some inspection inspection methods to detect detect and quantify certain types of deterioration. c. Selection Selection of inappropriat inappropriatee inspection inspection methods and tools. tools. d. Application Application of methods methods and tools by inadequate inadequately ly trained trained inspection personnel. e. Inadequate Inadequate inspection inspection procedures. procedures. f. Deteriorati Deterioration on rate under under some extremes extremes of conditi conditions ons is so high that failure failure can occur within a very very short time. Even though no deterioration is found during an inspection, failure could still occur as a result of a change or upset in conditions. For example, if a very aggressive acid is carried over from a corrosion resistant part of a system into a downstream vessel that is made of carbon steel, rapid corrosion could result in failure in a few hours or days. Similarly, if an aqueous chloride solution is carried into a sensitized stainless steel vessel, chloride stress corrosion cracking could occur very rapidly (depending on the temperature).

a. Pitting Pitting generally generally leads leads to small hole-si hole-sized zed leaks. leaks. b. Stress Stress corrosion corrosion cracking can develo develop p into small, through through wall cracks or, in some cases, catastrophic rupture. c. Metallurg Metallurgical ical deterioratio deterioration n and mechanical mechanical deteriorati deterioration on can lead to failure modes that vary from small holes to ruptures. d. General General thinning thinning from corrosion corrosion often leads leads to larger leaks leaks or rupture.

If multiple inspections have been performed, it is important to recognize that the most recent inspection may best reflect current operating conditions. If operating conditions have have changed, deterioration rates based on inspection data from the previous operating conditions may not be valid. Determination of inspection effectiveness should consider the following: 1. Equipm Equipment ent type. type. 2. Active Active and credible credible deterioration deterioration mechanism mechanism(s). (s). 3. Rate of deteriora deterioration tion or suscepti susceptibilit bility. y. 4. NDE methods, methods, coverage coverage and and frequency frequency.. 5. Accessibili Accessibility ty to expected expected deterioratio deterioration n areas. The effectiveness of future inspections can be optimized by utilization of NDE methods better suited for the active/credible deterioration mechanisms, adjusting the inspection coverage, adjusting the inspection frequency or some combination.

Failure mode primarily affects the magnitude of the consequences. For this and other other reasons, the probability and consequence analyses should be worked interactively. interactively.

9.4.4 9.4 .4 Calcul Calculate ate the the Probab Probabili ility ty of Fail Failure ure by by Deterioration Type

9.4. 9.4.2 2 Dete Determ rmin ine e Fail Failur ure e Mode Mode Probability of failure analysis is used to evaluate the failure mode (e.g., small hole, crack, catastrophic rupture) and the probability that each failure mode will occur. occur. It is important to link the deterioration mechanism to the most likely resulting failure mode. For example: example:

9.4.3 9.4 .3 Quanti Quantify fy Effecti Effectiven veness ess of Past Past Inspecti Inspection on Program Inspection programs (the combination of NDE methods such as visual, ultrasonic, radiographic etc., frequency and coverage/location of inspections) vary in their effectiveness for locating and sizing deterioration, and thus for determining deterioration rates. After the likely deterioration mechanisms

By combining the expected deterioration mechanism, rate or susceptibility, inspection data and inspection effectiveness, a probability of failure can now be determined for each deterioration type and failure mode. The probability of failure may be determined for future time periods or conditions as well as current. It is important for users to validate that the method used to calculate the POF is in fact thorough and adequate for the users’ needs.

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RISK-BASED INSPECTION ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

10 Ass Assess essing ing Conseq Conseque uence nces s of of Fail Failure ure 10.1 10. 1 INTRO INTRODUC DUCTIO TION N TO CONSE CONSEQUE QUENCE NCE ANALYSIS The consequence analysis in a RBI program is performed to provide discrimination between equipment items on the basis of the significance of a potential failure. In general, a RBI program will be managed by plant inspectors or inspection engineers, who will normally manage risk by managing the probability of failure with inspection and maintenance planning. They will not normally have much ability to modify the consequence of failure. On the other hand, management and process safety personnel may desire to manage the consequence side of the risk equation. Numerous methods for modifying the consequence of failure are mentioned in Section 13. For all of these users, the consequence analysis is an aid in establishing a relative risk ranking of equipment eq uipment items. The consequence analysis should be a repeatable, simplified, credible estimate of what might be expected to happen if a failure were to occur in the equipment item being assessed. More or less complex and detailed methods of consequence analysis can be used, depending on the desired application for the assessment. The consequence analysis method chosen should have a demonstrated ability to provide the required level of discrimination between higher and lower consequence equipment items.

10.1 10.1.1 .1 Loss Loss of Cont Contai ainm nmen entt The consequence of loss of containment is generally evaluated as loss of fluid to the external environment. The consequence effects for loss of containment can be generally considered to be in the following categories: a. b. c. d.

Safety Safety and and health health impac impact. t. Environmen Environmental tal impact. impact. Produc Productio tion n loss losses. es. Maintenance Maintenance and and reconstruct reconstruction ion costs. costs.

10.1.2 10. 1.2 Other Other Funct Function ional al Failu Failures res Although RBI is mainly concerned with loss of containment failures, other functional failures could be included in a RBI study if a user desired. Other functional failures could include: a. Functional Functional or mechanical mechanical failure failure of internal internal componen components ts of pressure containing equipment (e.g., column trays, demister mats, coalescer elements, distribution hardware, etc.). b. Heat exchanger exchanger tube failure. failure. Note: There may be situations where a heat exchanger tube failure could lead to a loss of containment of the heat exchanger or ancillary equipment. These would typically involve involve leakage from a high pressure side to a low pressure side of the exchanger and subsequent breach of containment of the low pressure side.


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c. Pressure Pressure relief relief device device failure failure.. d. Rotating Rotating equipment equipment failure failure (e.g., seal leaks, leaks, impeller failfailures, etc.). These other functional failures are usually covered within reliability centered maintenance (RCM) programs and therefore are not covered in detail in this document.

10.2 10. 2

TYPES YPES OF CONS CONSEQU EQUENC ENCE E ANAL ANALYSI YSIS S

The following paragraphs discuss different approaches to the determination of consequences of failure. For the purposes of the discussion, these approaches have been categorized as “qualitative” or “quantitative.” However, However, it should be recognized that “qualitative” and “quantitative” are the end points of a continuum rather than distinctive approaches (see Figure 3). 3).

10.2.1 10. 2.1 Quali Qualitat tative ive C Cons onsequ equenc ences es Analy Analysis sis A qualitative method involves identification of the units, systems or equipment, and the hazards present as a result of operating conditions and process fluids. On the basis of expert knowledge and experience, the consequences of failure (safety, health, environmental or financial impacts) can be estimated separately for each unit, system, equipment group or individual equipment item. For a qualitative method, a consequences category (such as “A” through “E” or “high”, “medium” or “low”) is typically assigned for each unit, system, grouping or equipment item. It may be appropriate to associate a numerical value, such as cost (see 10.3.2), with each consequence category.

10.2.2 10. 2.2 Quant Quantita itativ tive e Conseq Consequen uences ces Analy Analysis sis A quantitative method involves using a logic model depicting combinations of events to represent the effects of failure on people, property, the business and the environment. Quantitative models usually contain one or more standard failure scenarios or outcomes and calculate consequence of failure based on: a. Type of process process fluid in in equipment. equipment. b. State of the process process fluid inside inside the equipment equipment (solid, (solid, liquid or gas). c. Key properti properties es of process fluid fluid (molecular (molecular weight, boiling boiling point, autoignition temperature, ignition energy, density, density, etc.). d. Process Process operating operating variables variables such as temperat temperature ure and pressure. e. Mass of invento inventory ry availabl availablee for release in the event event of a leak. f. Failure Failure mode mode and and resulti resulting ng leak leak size. size. g. State of fluid fluid after release release in ambient ambient conditions conditions (solid, (solid, gas or liquid).


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Results of a quantitative analysis are usually numeric. Consequence categories may be also used to organize more quantitatively assessed consequences into manageable groups.

10.3 10. 3

UNITS OF UNITS OF MEASU MEASURE RE IIN N CONS CONSEQU EQUENC ENCE E ANALYSIS

Different types of consequences may be described best by different measures. The RBI analyst should consider the nature of the hazards present and select appropriate units of measure. However, the analyst should bear in mind that the resultant consequences should be comparable, as much as possible, for subsequent risk prioritization. The following provide some units of measure of consequence that can be used in a RBI assessment.

10.3.1

Safety

Safety consequences are often expressed as a numerical value or characterized by a consequence category associated with the severity of potential injuries that may result from an undesirable event. For example, safety consequences could be expressed based on the severity of an injury (e. (e.g., g., fatality, serious injury, medical treatment, first aid) or expressed as a category linked to the injury severity (e.g., A through E).

10.3.2

Cost

Cost is commonly used as an indicator of potential consequences. It is possible, although not always credible, to assign costs to almost any type of consequence. Typical consequences that can be expressed in “cost” include: a. Production Production loss loss due to rate reductio reduction n or downtime. downtime. b. Deployment Deployment of emergency emergency response response equipment equipment and personnel. c. Lost Lost product product from from a releas release. e. d. Degradation Degradation of product product quality quality.. e. Replacement Replacement or or repair repair of damaged damaged equipment equipment.. f. Proper Property ty dama damage ge offsi offsite. te. g. Spill/relea Spill/release se cleanup cleanup onsite onsite or offsite. offsite. h. Business Business interrupti interruption on costs (lost (lost profits). profits). i. Loss Loss of of mark market et sha share re.. j. Injuries Injuries or fatalities fatalities.. k. Land Land recla reclamat mation ion.. l. Liti Litiga gati tion on.. m. Fines. Fines. n. Good Goodwi will ll.. The above list is reasonably comprehensive, but in practice some of these costs are neither practical nor necessary to use in a RBI assessment. Cost generally requires fairly detailed information to fully assess. Information such as product value, equipment costs, repair costs, personnel resources, and environmental damage

may be difficult to derive, and the manpower required to perform a complete financial-based consequence analysis may be limited. However, cost has the advantage of permitting a direct comparison of various types of losses on a common basis.

10.3 10.3.3 .3 Affe Affect cted ed Area Area Affected area is also used to describe potential consequences in the field of risk assessment. As its name implies, affected area represents the amount of surface area that experiences an effect (toxic dose, thermal radiation, explosion overpressure, etc.) greater than a pre-defined limiting value. Based on the thresholds chosen, anything — personnel, equipment, environment — within the area will be affected by the consequences of the hazard. In order to rank consequences according to affected area, it is typically assumed that equipment or personnel at risk are evenly distributed throughout the unit. A more rigorous approach would assign a population density with time or equipment value density to different areas of the unit. The units for affected area consequence (square feet or square meters) do not readily translate into our everyday experiences and thus there is some reluctance to use this measure. It has, however, several features that merit consideration. The affected area approach has the characteristic of being able to compare toxic and flammable consequences by relating to the physical area impacted by a release.

10.3 10.3.4 .4 Envi Enviro ronm nmen enta tall Damage Damage Environmental consequence measures are the least developed among those currently used for RBI. A common unit of measure for environmental damage is not available in the current technology, making environmental consequences difficult to assess. Typical parameters used that provide an indirect measure of the degree of environmental damage are: a. Acres of of land affected affected per per year. year. b. Miles of shoreli shoreline ne affected affected per year year.. c. Number of biologic biological al or human-use human-use resources resources consumed consumed.. The portrayal of environmental damage almost invariably leads to the use of cost, in terms of dollars per year, for the loss and restoration of environmental resources.

10.4 10. 4 VOLUME OLUME OF FLUID FLUID RELEAS RELEASED ED In most consequence evaluations, a key element in determining the magnitude of the consequence is the volume of fluid released. The volume released is typically derived from a combination of the following: a. Volume of fluid available available for release – Volume of fluid in the piece of equipment and connected equipment items. In theory, this is the amount of fluid between isolation valves that can be quickly closed. b. Fail Failur uree mode. mode.

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c. Leak Leak rate rate.. d. Detection Detection and and isolati isolation on time. time. In some cases, the volume released will be the same as the volume available for release. Usually, there are safeguards and procedures in place so that the breach of containment can be isolated and the volume released will be less than the volume available for release.

10.5 10. 5 CONSE CONSEQUE QUENCE NCE EFFECT EFFECT CATEGO CATEGORIE RIES S The failure of the pressure boundary and subsequent release of fluids may cause safety, health, environmental, facility and business damage. The RBI analyst should consider the nature of the hazards and assure that appropriate factors are considered for the equipment, system, unit or plant being assessed. Regardless of whether a more qualitative or quantitative analysis is used, the major factors to consider in evaluating the consequences of failure are listed in the following sections.

10.5.1 10. 5.1 Flamma Flammabl ble e Events Events (Fire (Fire and and Explos Explosion ion))

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nel injuries. The RBI program typically focuses on acute toxic risks that create an immediate danger, rather than chronic risks from low-level exposures. The toxic consequence is typically derived from the following elements: a. Volume of fluid fluid released released and toxicity toxicity.. b. Ability Ability to disperse under under typical process process and environm environmenental conditions. c. Detection Detection and and mitigati mitigation on systems. systems. d. Population Population in the the vicinity vicinity of the the release. release.

10.5.3 10. 5.3 Rel Release eases s of Othe Otherr Hazard Hazardous ous Flui Fluids ds Other hazardous fluid releases are of most concern in RBI assessments when they affect personnel. These materials can cause thermal or chemical burns if a person comes in contact with them. Common fluids, including steam, hot water, acids and caustics can have a safety consequence of a release and should be considered as part of a RBI program. Generally, the consequence of this type of release is significantly lower than for flammable or toxic releases because the affected area is likely to be much smaller and the magnitude of the hazard is less. Key parameters in this evaluation are:

Flammable events occur when both a leak and ignition occurs. The ignition could be through an ignition source or auto-ignition. Flammable events can cause damage in two ways: thermal radiation and blast overpressure. Most of the damage from thermal effects tends to occur at close range, but blast effects can cause damage over a larger distance from the blast center. Following are typical categories of fire and explosion events:

a. Volume of fluid fluid release released. d. b. Personnel Personnel density density in the the area. area. c. Type of fluid and and nature of resulti resulting ng injury. injury. d. Safety Safety systems (e.g., personnel personnel protectiv protectivee clothing, showshowers etc.).

a. b. c. d. e.

e. Environme Environmental ntal damage damage if the spill spill is not contained contained.. f. Equipment Equipment damage. damage. For some reacti reactive ve fluids, fluids, contact contact with equipment or piping may result in aggressive deterioration and failure.

Vapor cloud explosion. explosion. Pool Pool fire. fire. Jet Jet fir fire. Flas Flash h fire. fire. Boiling Boiling liquid expandi expanding ng vapor vapor explosion explosion (BLEVE). (BLEVE).

The flammable events consequence is typically derived from a combination of the following elements: 1. Inherent Inherent tendenc tendency y to ignite. ignite. 2. Volume of fluid fluid released. released. 3. Ability Ability to flash flash to to a vapor vapor.. 4. Possibility Possibility of auto-igniti auto-ignition. on. 5. Effects Effects of higher pressure pressure or higher higher temperatur temperaturee operations. 6. Engine Engineere ered d safegu safeguard ards. s. 7. Personnel Personnel and equipme equipment nt exposed exposed to damage. damage.

10.5 10.5.2 .2 Toxic xic Relea Release ses s Toxic releases, in RBI, are only addressed when they affect personnel (site and public). These releases can cause effects at greater distances than flammable events. Unlike flammable releases, toxic releases do not require an additional event (e.g., ignition, as in the case of flammables) to cause person-


Other considerations in the analysis are:

10.5.4 10. 5.4 Envir Environ onmen mental tal Conseq Consequen uences ces Environmental consequences are an important component to any consideration of overall risk in a processing plant. The RBI program typically focuses on acute and immediate environmental risks, rather than chronic risks from low-level emissions. The environmental consequence is typically derived from the following elements: a. Volume of fluid fluid release released. d. b. Ability Ability to flash to to vapor vapor.. c. Leak containment containment safeguards safeguards.. d. Environme Environmental ntal resources resources affected affected.. e. Regulatory Regulatory consequenc consequencee (e.g., citations citations for violations, violations, fines, potential shutdown by authorities). Liquid releases may result in contamination of soil, groundwater and/or open water. Gaseous releases are equally important but more difficult to assess since the consequence


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typically relates to local regulatory constraints and the penalty for exceeding those constraints. The consequences of environmental damage are best understood by cost. The cost may be calculated as follows: Environmental Cost = Cost for cleanup + Fines + Other costs The cleanup cost will vary depending on many factors. Some key factors are: 1. Type of spill—above spill—above ground, ground, below below ground, surface surface water etc. 2. Type of liquid liquid.. 3. Method Method of clea cleanup. nup. 4. Volume olume of spill spill.. 5. Accessibility Accessibility and and terrain terrain at the spill locati location. on. ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

The fine component cost will depend on the regulations and laws of the applicable local and federal jurisdictions. The other cost component would include costs that may be associated with the spill such as litigation from landowners or other parties. This component is typically specific to the locale of the facility. facility.

More rigorous methods for estimating business interruption consequences may take into account factors such as: a. Ability Ability to compensate compensate for damaged damaged equipment equipment (e.g., (e.g., spare equipment, rerouting, etc.). b. Potential Potential for damage damage to nearby nearby equipment equipment (knock-on (knock-on damage). c. Potential Potential for product production ion loss loss to other other units. units. Site specific circumstances should be considered in the business interruption analysis to avoid over or under stating this consequence. Examples of these considerations include: 1. Lost producti production on may be compensa compensated ted at another another underutilized or idle facility. facility. 2. Loss of profit profit could be compounded compounded if other other faciliti facilities es use the unit’s output as a feedstock or processing fluid. 3. Repair of of small damage damage cost cost equipment equipment may may take as long as large damage cost equipment. 4. Extended Extended downtime downtime may result result in losing losing customers customers or market share, thus extending loss of profit beyond production restart. 5. Loss of hard hard to get or unique unique equipment equipment items items may require extra time to obtain replacements. 6. Insura Insurance nce cover coverage age..

10.5.5 10. 5.5 Produ Producti ction on Conseq Consequen uences ces

10.5.6 10. 5.6 Mainte Maintenan nance ce and Recon Reconstr struct uction ion Impac Impactt

Production consequences generally occur with any loss of containment of the process fluid and often with a loss of containment of a utility fluid (water, steam, fuel gas, acid, caustic etc). These production consequences may be in addition to or independent of flammable, toxic, hazardous or environmental consequences. The main production consequences for RBI are financial. The financial consequences could include the value of the lost process fluid and business interruption. The cost of the lost fluid can be calculated fairly easily by multiplying the volume released by the value. Calculation of the business interruption is more complex. The selection of a specific method depends on:

Maintenance and reconstruction impact represents the effort required to correct the failure and to fix or replace equipment damaged in the subsequent events (e.g., fire, explosion). The maintenance and reconstruction impact should be accounted for in the RBI program. Maintenance impact will generally be measured in monetary terms and typically includes:

a. The scope scope and level level of detail detail of of the study study.. b. Availabilit vailability y of business interrupt interruption ion data. A simple method for estimating the business interruption consequence is to use the equation: Business Interruption = Process Unit Daily D aily Value Value x Downtime (Days)

a. Repa Repair irs. s. b. Equipme Equipment nt replac replaceme ement. nt.

11 Risk Risk Deter Determin minati ation, on, Ass Assess essmen mentt and and Management 11.1 PURPOSE This section describes the process of determining risk by combining the results of work done as described in Section 9 and 10. It also provides guidelines for prioritizing and assessing the acceptability of risk with respect to risk criteria. This work process leads to creating and implementing a risk management plan.

11.2 11.2 DE DETE TERM RMIN INAT ATIO ION N OF OF RIS RISK K The Unit Daily Value could be on a revenue or profit basis. The downtime estimate would represent the time required to get back into production. The Dow Fire and Explosion Index is a typical method of estimating downtime after a fire or explosion.


11.2.1 11. 2.1 Determ Determina inatio tion n of the the Probab Probabili ility ty of a Specific Consequence Once the probabilities of failure and failure mode(s) have been determined for the relevant deterioration mechanisms



` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

(see Section 9), the probability of each credible consequence scenario should be determined. In other words, the loss of containment failure may only be the first event in a series of events that lead to a specific consequence. The probability of credible events leading up to the specific consequence should be factored into the probability of the specific consequence occurring. For example, after a loss of containment the first event may be initiation or failure of safeguards (isolation, alarms, etc.). The second event may be dispersion, dilution or accumulation of the fluid. The third event may be initiation of or failure to initiate preventative action (shutting down nearby ignition sources, neutralizing the fluid, etc) and so on until the specific consequence event (fire, toxic release, injury, environmental release etc.) It is important to understand this linkage between the probability of failure and the probability of possible resulting incidents. The probability of a specific consequence is tied to the severity of the consequence and may differ considerably from the probability of the equipment failure itself. Probabilities of incidents generally decrease with the severity of the incident. For example, the probability of an event resulting in a fatality will generally be less than the probability that the event will result in a first aid or medical treatment injury. It is important to understand this relationship. Personnel inexperienced in risk assessment methods often link the probability of failure with the most severe consequences that can be envisioned. An extreme example would be coupling the POF of a deterioration mechanism where the mode of failure is a small hole leak with the consequence of a major fire. This linkage would lead to an overly conservative risk assessment since a small leak will rarely lead to a major fire. Each type of deterioration mechanism has its own characteristic failure mode(s). For a specific deterioration mechanism, the expected mode of failure should be taken into account when considering the probability of incidents in the aftermath of an equipment failure. For instance, the consequences expected from a small leak could be very different than the consequences expected from a brittle fracture. The following example serves to illustrate how the probability of a specific consequence could be determined. The example has been simplified and the numbers used are purely hypothetical. Suppose a piece of equipment containing hydrocarbons is being assessed. An event tree starting with a loss of containment could be depicted as shown in Figure in Figure 5. The probability of the specific consequence is the product of the probability of each event leading up to the specific consequence. In the example, the specific consequence being evaluated is a fire. The probability of a fire would be: Probability of Fire = (Probability of Failure) x (Probability of Ignition)


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Probability of Fire = 0.001 per year x 0.01 = 0.00001 or 1 x 10-5 per year The probability of no fire encompasses two scenarios (loss of containment and no loss of containment). The probability of no fire would be: Probability of No Fire = (Probability of Failure x Probability of Non-ignition) + Probability of No Failure Probability of No Fire = (0.001 per year x 0.99) + 0.999 per year = 0.99999 per year Note: The probability of all consequence scenarios should equal 1.0. In the example, the probability of the specific consequence of a fire (1 x 10-5 per year) plus the probability of no fire (9.9999 x 10-1per year) equals 1.0.

Typically, there will be other credible consequences that should be evaluated. However, it is often possible to determine a dominant probability/consequence pair, such that it is not necessary to include every credible scenario in the analysis. Engineering judgment and experience should be used to eliminate trivial cases.

11.2 11.2.2 .2 Ca Calc lcul ulat ate e Ris Risk k Referring back to the Risk equation: Risk = Probability x Consequence it is now possible to calculate the risk for each specific consequence. The risk equation can now be stated as: Risk of a specific consequence = (Probability of a specific consequence) x (Specific Consequence) The total risk is the sum of the individual risks for each specific consequence. Often one probability/consequence pair will be dominant and the total risk can be approximated by the risk of the dominant scenario. For the example mentioned in 11.2.1, if the consequence of a fire had been assessed at $1 x 107 then the resulting risk would be: Risk of Fire = (1 x 10-5 per year) x ($1 x 107) = $100/year If probability and consequence are not expressed as numerical values, risk is usually determined by plotting the probability and consequence on a risk matrix (see 11.6). Probability and consequence pairs for various scenarios may be plotted to determine risk of each scenario. Note that when a risk matrix is used, the probability to be plotted should be


28


the probability of the associated consequence, not the probability of failure.

process. Refer to Section 12 for a more detailed description of inspection planning based on risk analysis.

11.3 11. 3

11.4 11.4 SENS SENSIT ITIV IVIT ITY Y ANALY ANALYSI SIS S

RISK RISK MANA MANAGEM GEMENT ENT DEC DECISI ISIONS ONS AND ACCEPTABLE LEVELS OF RISK

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11.3 11.3.1 .1 Risk Risk Acc Accep epta tanc nce e Risk-based inspection is a tool to provide an analysis of the risks of loss of containment of equipment. Many companies have corporate risk criteria defining acceptable and prudent levels of safety, environmental and financial risks. These risk criteria should be used when making risk-based inspection decisions. Because each company may be different in terms of acceptable risk levels, risk management decisions can vary among companies. Cost-benefit analysis is a powerful tool that is being used by many companies, governments and regulatory authorities as one method in determining risk acceptance. Users are referred to "A Comparison of Criteria for Acceptance of Risk" by the Pressure Vessel Research Council, for more information on risk acceptance. Risk acceptance may vary for different risks. For example, risk tolerance for an environmental risk may be higher than for a safety/health risk.

11.3.2 11. 3.2 Using Using Risk Risk Ass Assessm essment ent in in Inspec Inspectio tion n and Maintenance Planning The use of risk assessment in inspection and maintenance planning is unique in that consequential information, which is traditionally operations-based, and probability of failure information, which is typically engineering/maintenance/inspection-based, is combined to assist in the planning process. Part of this planning process is the determination of what to inspect, how to inspect (technique), and the extent of inspection (coverage). Determining the risk of process units, or individual process equipment items facilitates this, as the inspections are now prioritized based on the risk value. The second part of this process is determining when to inspect the equipment. Understanding how risk varies with time facilitates this part of the

Understanding the value of each variable and how it influences the risk calculation is key to identifying which input variables deserve closer scrutiny versus other variables which may not have significant effects. This is more more important when performing risk analyses that are more detailed and quantitative in nature. Sensitivity analysis typically involves reviewing some or all input variables to the risk calculation to determine the overall influence on the resultant risk risk value. Once this analysis has been performed, the user can see which input variables significantly influence the risk value. Those key input variables deserve the most focus or attention. It often is worthwhile to gather additional information on such variables. Typically, the preliminary estimates of probability and consequence may be too conservative or too pessimistic; therefore, the information gathering performed after the sensitivity analysis should be focused on developing more certainty for the key input variables. variables. This process should ultimately lead to a re-evaluation of the key input variables. As such, the quality and accuracy of the risk analysis should improve. This is an important part of the data validation phase of risk assessment.

11.5 11.5 AS ASS SUM UMP PTION IONS Assumptions or estimates of input values are often used when consequence and/or probability of failure data are not available. Even when data are known to exist, exist, conservative estimates may be utilized in an initial analysis pending input of future process or engineering modeling information, such as a sensitivity sensitivity analysis. Caution is advised in being too conservative, as overestimating consequences and/or probability of failure values will unnecessarily inflate the calculated risk values. Presenting over over inflated risk values values may mislead inspection planners, management and insurers, and can create a lack of credibility for the user and the RBI process.

Loss of containment Probability of failure = 1/1000 = 0.001/year

No fire

Fire

Probability of non-ignition = 99/100 = 0.99

Probability of Ignition = 1/100 = 0.01

Figure 5—Example 5—Example Event Event Tree




29

Qualitative Risk Matrix 5

Higher risk

4

Medium risk

y 3 r o g e t a c y t i l i b 2 a b o r P

Lower risk

1

A

B

C

D

E

Consequence category

Figure 6—Example 6—Example Risk Matrix Using Probability Probability and Consequence Consequence Categories Categories to Display Risk Rankings Rankings

11.6 11.6 RISK RISK PR PRES ESEN ENTA TATI TION ON

11. 11.6.2 6.2

Once risk values are developed, they can then be presented in a variety of ways to communicate the results of the analysis to decision-makers and inspection planners. One goal of the risk analysis is to communicate the results in a common format that a variety of people can understand. Using a risk matrix or plot is helpful in accomplishing this goal.

When more quantitative consequence and probability data are being used, and where showing numeric risk values is more meaningful to the stakeholders, a risk plot (or graph) is used (Figure 7). This graph is constructed similarly to the risk matrix in that the highest risk is plotted toward the upper right-hand corner. Often a risk plot is drawn using log-log scales for a better understanding of the relative risks of the items assessed. In the example plot in in Figure 7, ten pieces of equipment are shown, as well as an iso-risk line (line of constant risk). If this line is the acceptable threshold of risk in this example, then equipment items 1, 2 and an d 3 should be mitigated so that their resultant risk levels fall below the line.

11.6 11.6.1 .1 Risk Risk Ma Matr trix ix For risk ranking methodologies that use consequence and probability categories, presenting the results in a risk matrix is a very effective way of communicating the distribution of risks throughout a plant or process unit without numerical values. An example risk matrix is shown in Figure 6. In this figure, the consequence and probability categories are arranged such that the highest risk ranking is toward the upper right-hand corner. It is usually desirable to associate numerical values with the categories to provide guidance to the personnel performing the assessment (e.g., probability category C ranges from 0.001 to 0.01). Different sizes of matrices may be used (e.g., 5 x 5, 4 x 4, etc.). Regardless of the matrix selected, the consequence and probability categories should provide sufficient discrimination between the items assessed. Risk categories may be assigned to the boxes on the risk matrix. An example risk categorization (higher, medium, lower) of the risk matrix is shown in Figure 6. In this example the risk categories are symmetrical. They may also be asymmetrical where for instance the consequence category may be given higher weighting than the probability category.


11.6. 11. 6.3 3

Risk isk Plots lots

Usin Using g a Risk Risk Plo Plott or Mat Matri rix x

Equipment items residing towards the upper right-hand corner of the plot or matrix (in the examples presented) will most likely take priority for inspection planning because these items have have the highest risk. Similarly, Similarly, items residing toward the lower left-hand corner of the plot (or matrix) will tend to take lower priority because these items have the lowest risk. Once the plots have been completed, the risk plot (or matrix) can then be used as a screening tool during the prioritization process.

11.7 11. 7

ESTAB ESTABLIS LISHIN HING G AC ACCEP CEPTA TABL BLE E RI RISK SK THRESHOLDS

After the risk analysis has been performed, and risk values plotted, the risk risk evaluation evaluation process begins. Risk plots and matrices can be used to screen, and initially identify higher,


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30


c. Consequence Consequence mitigatio mitigation: n: Can actions actions be taken to lessen lessen the consequences related to an equipment failure? d. Probability Probability mitigati mitigation: on: Can actions actions be taken to lessen the probability of failure such as metallurgy changes or equipment redesign?

Risk plot

ISO-risk line 1

e r u l i a f f o y t i l i b a b o r P

Risk management decisions can now be made on which mitigation actions(s) to take. Risk management/mitigation is covered further in Sections 12 and 13.

2

6

12 Risk Risk Manag Manageme ement nt with with Inspec Inspectio tion n Activities

5 7

12.1 12. 1 4 9 10

8

3

Consequence of failure

Figure 7—Risk Plot Plot when Using Using Quantitativ Quantitative e or Numeric Risk Values intermediate and lower risk equipment items. The equipment can also be ranked (prioritized) according to its risk value in tabular form. Thresholds that divide the risk plot, matrix or table into acceptable and unacceptable regions of risk can be developed. Corporate safety and financial policies and constraints or risk criteria influence the placement of the thresholds. Regulations and laws may also specify or assist in identifying the acceptable risk thresholds. Reduction of some risks to an acceptable level may not be practical due to technology and cost constraints. An “As Low As Reasonably Practical” (ALARP) approach to risk management or other risk management approach may be necessary for these items.

11.8 11.8 RISK RISK MA MANA NAGE GEME MENT NT Based on the ranking of items and the risk threshold, the risk management process begins. For risks that are judged acceptable, no mitigation may be required and no further action necessary. For risks considered unacceptable and therefore requiring risk mitigation, there are various mitigation categories that should be considered: a. Decommission Decommission:: Is the the equipment equipment really really necessary necessary to supsupport unit operation? b. Inspection/ Inspection/condit condition ion monitoring: monitoring: Can a cost-effecti cost-effective ve inspection program, with repair as indicated by the inspection results, be implemented that will reduce risks to an acceptable level?

MANAGING MANAG ING RISK RISK BY BY REDU REDUCIN CING G UNCERTAINTY THROUGH INSPECTION

In previous sections, it has been mentioned that risk can be managed by inspection. Obviously, Obviously, inspection does not arrest or mitigate deterioration mechanisms. mechanisms. Inspection serves to identify, monitor, and measure the deterioration mechanism(s). Also, it is invaluable invaluable input in the prediction of when the deterioration will reach a critical point. Correct application of inspections will improve the user's ability to predict the deterioration mechanisms mechanisms and rates of deterioration. The better the predictability, the less uncertainty there will be as to when a failure may occur. Mitigation (repair, replacement, changes etc.) can then be planned and implemented prior to the predicted failure failure date. The reduction in uncertainty and increase in predictability through inspection translate directly into a reduction in the probability of a failure and therefore a reduction in the risk. However, users should be diligent to assure that temporary inspection alternatives, in lieu of more permanent risk reductions, are effective. Risk mitigation achieved through inspection presumes that the organization will act on the results of the inspection in a timely manner. manner. Risk mitigation is not achieved if inspection data that are gathered are not properly analyzed and acted upon where needed. The quality of the inspection data and the analysis or interpretation will greatly affect the level of risk mitigation. Proper inspection methods and data analysis tools are therefore critical.

12.2 12. 2 IDENTI IDENTIFYI FYING NG RISK RISK MANA MANAGEM GEMENT ENT OPPORTUNITIES FROM RBI AND PROBABILITY OF FAILURE RESULTS As discussed in Section 11, typically a risk priority list is developed. RBI will also identify whether consequence or probability of failure or both is driving driving risk. In the situations where risk is being driven by probability of failure, there is usually potential for risk management through inspection. Once a RBI assessment has been completed, the items with higher or unacceptable risk should be assessed for potential

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31

risk management through inspection. Whether inspections will be effective or not will depend on:

raphy, etc. will be more effective. The level of risk reduction achieved by inspection will depend on:

a. Equi Equipm pmen entt type. type. b. Active Active and credible credible deterioration deterioration mechanism( mechanism(s). s). c. Rate of deteriora deterioration tion or suscepti susceptibilit bility. y. d. Inspection Inspection methods, methods, coverage coverage and frequency frequency. e. Accessibili Accessibility ty to expected expected deteriora deterioration tion areas. areas. f. Shutdow Shutdown n requi requirem rement ents. s. g. Amount of achieva achievable ble reduction reduction in probability probability of failure failure (POF) (i.e., a reduction in POF of a low POF item may be difficult to achieve through inspection). Depending on factors such as the remaining life of the equipment and type of deterioration mechanism, risk management through inspection may have little or no effect. Examples of such cases are:

a. Mode of failure failure of the the deterioratio deterioration n mechanism. mechanism. b. Time Time interval interval between the onset onset of deterioratio deterioration n and failure, (i.e., speed of deterioration). c. Detection Detection capability capability of inspect inspection ion technique. technique. d. Scope Scope of insp inspect ection ion.. e. Freque Frequency ncy of insp inspect ection ion..

1. Corrosion Corrosion rates well-esta well-establishe blished d and equipment nearnearing end of life. 2. Instantaneo Instantaneous us failures failures related to operating operating conditions conditions such as brittle fracture. 3. Inspection Inspection technology technology that that is not sufficient sufficient to detect detect or quantify deterioration adequately. 4. Too short a time frame frame from the onset onset of deteriorati deterioration on to final failure for periodic inspections to be effective (e.g., high-cycle fatigue cracking). 5. Event-dri Event-driven ven failures failures (circumstan (circumstances ces that cannot be predicted). In cases such as these, an alternative form of mitigation may be required. The most practical and cost effective risk mitigation strategy can then be developed for each item. Usually, inspection provides a major part of the overall risk management strategy.

12.3 12. 3 ESTAB ESTABLIS LISHIN HING G AN INSPECTI INSPECTION ON STRATE STRATEGY GY BASED ON RISK ASSESSMENT The results of a RBI assessment and the resultant risk management assessment may be used as the basis for the development of an overall inspection strategy for the group of items included. The inspection strategy strategy should be designed in con junction junction with other mitigation mitigation plans so that all equipment equipment items will have resultant risks that are acceptable. Users should consider risk rank, risk drivers, item history, number and results of inspections, type and effectiveness of inspections, equipment in similar service and remaining life in the development of their inspection strategy. Inspection is only effective if the inspection technique chosen is sufficient for detecting the deterioration mechanism and its severity. severity. As an example, spot thickness readings on a piping circuit would be considered to have little or no benefit if the deterioration mechanism results in unpredictable localized corrosion (e.g., pitting, ammonia bisulfide corrosion, local thin area, etc.). In this case, ultrasonic scanning, radiog-


Organizations should be deliberate and systematic in assigning the level of risk management achieved through inspection and should be cautious not to assume that there is an unending capacity for risk management through inspection. The inspection strategy should be a documented, iterative process to assure that inspection activities are continually focused on items with higher risk and that the risks are effectively reduced by the implemented inspection activity.

12.4 12. 4

MANAG MAN AGING ING RISK RISK WITH WITH INSP INSPECT ECTION ION ACTIVITIES

The effectiveness of past inspections is part of the determination of the present risk. The future risk can now be impacted by future inspection activities. activities. RBI can be used as a “what if” tool to determine when, what and how inspections should be conducted to yield an acceptable future risk level. Key parameters and examples that can affect the future risk are: a. Frequency Frequency of inspectio inspection n – Increasing Increasing the frequency frequency of inspections may serve to better define, identify or monitor the deterioration mechanism(s) and therefore reduce the risk. Both routine and turnaround inspection frequencies can be optimized. b. Coverage Coverage – Different Different zones zones or areas of inspecti inspection on of an item or series of items can be modeled and evaluated to determine the coverage that will produce an acceptable level of risk. For example: 1. A high risk piping piping system system may may be a candidate candidate for extensive inspection, using one or more NDE techniques targeted to locating the identified deterioration mechanisms. 2. An assessment assessment may may reveal reveal the need need for focus focus on parts of a vessel where the highest risk may be located and focus on quantifying this risk rather than look at the rest of the vessel where there are perhaps only low risk deterioration processes occurring. c. Tools and techniqu techniques es – The selectio selection n and usage of the the appropriate inspection tools and techniques can be optimized to cost effectively and safely reduce risk. In the selection of inspection tools and techniques, inspection personnel should take into consideration that more than one technology may achieve risk risk mitigation. However, However, the level level of mitigation


32


achieved can vary vary depending on the choice. As an example, radiography may be more effective than ultrasonic for thickness monitoring in cases of localized corrosion. d. Procedures Procedures and practices practices – Inspection Inspection procedur procedures es and the actual inspection practices can impact the ability of inspection activities to identify, measure and/or monitor deterioration mechanisms. If the inspection activities are executed effectively by well-trained and qualified inspectors, the expected risk management should be obtained. The user is cautioned not to assume that all inspectors and NDE examiners are well qualified and experienced, but rather to take steps to assure that they have the appropriate level of experience and qualifications. e. Internal Internal or external external inspection inspection – Risk reductio reductions ns by both internal and external inspections should be assessed. Often external inspection with effective on-stream inspection techniques can provide useful data for risk assessment. It is worth noting that invasive inspections, in some cases, may cause deterioration and increase the risk of the item. Examples where this may happen include: 1. Moisture Moisture ingress ingress to equipment equipment leading leading to SCC or polypolythionic acid cracking. 2. Internal Internal inspection inspection of glass glass lined lined vessels. vessels. 3. Removal Removal of passi passivati vating ng films. films. 4. Human errors in re-stre re-streaming. aming. 5. Risk associated associated with with shutting shutting down and and starting starting up equipment. The user can adjust these parameters to obtain the optimum inspection plan that manages risk, is cost effective, and is practical.

12.5 12. 5

MANAGI MAN AGING NG INSPE INSPECT CTION ION COST COSTS S WITH WITH RBI RBI

Inspection costs can be more effectively managed through the utilization of RBI. Resources can be applied or shifted to those areas identified as a higher risk or targeted based on the strategy selected. Consequently, this same strategy allows consideration for reduction of inspection activities in those areas that have a lower risk or where the inspection activity has little or no affect on the associated risks. This results in inspection resources being applied where they are needed most. Another opportunity for managing inspection costs is by identifying items in the inspection plan that can be inspected non-intrusively on-stream. If the non-intrusive non-intrusive inspection provides sufficient risk management, then there is a potential for a net savings based on not having to blind, open, clean, and internally inspect during downtime. If the item considered is the main driver for bringing an operational unit down, then the non-intrusive inspection may contribute to increased uptime of the unit. The user should recognize that while there is a potential for the reduction of inspection costs through the utilization of RBI, equipment integrity and inspection cost optimization should remain the focus. ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -


12.6 12. 6 ASSESS ASSESSING ING INSP INSPECT ECTION ION RES RESULT ULTS S AND DETERMINING CORRECTIVE ACTION Inspection results such as deterioration mechanisms, rate of deterioration and equipment tolerance to the types of deterioration should be used as variables in assessing remaining life and future inspection plans. The results can also be used for comparison or validation of the models that may have been used for probability of failure determination. A documented mitigation action plan should be developed for any equipment item requiring repair or replacement. The action plan should describe the extent of repair (or replacement), recommendations, the proposed repair method(s), appropriate appropriate QA/QC and the date the plan should be completed.

12.7 12. 7

ACHIEVIN ACHIE VING G LOWEST LOWEST LIF LIFE E CYCLE CYCLE COSTS COSTS WITH RBI

Not only can RBI be used to optimize inspection costs that directly affect life cycle costs, it can assist in lowering overall life cycle costs through various various cost benefit assessments. The following examples can give a user ideas on how to lower life cycle costs through RBI with cost benefit assessments. a. RBI should enhance enhance the predicti prediction on of failures failures caused caused by deterioration mechanisms. This in turn should give the user confidence to continue to operate equipment safely, closer to the predicted failure date. By doing this, the equipment cycle time should increase and life cycle costs decrease. b. RBI can be used to assess assess the effects effects of changing changing to a more aggressive fluid. A subsequent plan to upgrade construction material or replace specific items can then be developed. The construction material plan would consider the optimized run length safely attainable along with the appropriate inspection plan. This could equate to increased profits and lower life cycle costs through reduced maintenance, optimized inspections, and increased unit/equipment uptime. c. Turnaroun Turnaround d and maintenance maintenance costs costs also have have an affect on the life cycle costs of an equipment item. By using the results of the RBI inspection plan to identify more accurately where to inspect and what repairs and replacements to expect, turnaround and maintenance work can be preplanned and, in some cases, executed at a lower cost than if unplanned.

13 Other Other Ris Risk k Mitiga Mitigatio tion n Activi Activitie ties s 13.1 GENERAL As described in the previous section, inspection is often an effective method of risk management. However, inspection may not always provide sufficient risk mitigation or may not be the most cost effective method. The purpose of this section is to describe other methods of risk mitigation. This list is not



33

meant to be all inclusive. These risk mitigation activities fall into one or more of the following:

13.6 13. 6

a. Reduce the magnitu magnitude de of consequence. consequence. b. Reduce the probabili probability ty of failur failure. e. c. Enhance the the survivabili survivability ty of the facility facility and people to the consequence. d. Mitigate Mitigate the primary primary source source of consequence consequence..

This method reduces the amount and rate of release. Like emergency isolation, the emergency depressurizing and/or de-inventory needs to be achieved within a few minutes to affect explosion/fire risk.

13.2 13. 2 EQUIPM EQUIPMENT ENT REPL REPLACE ACEMEN MENT T AND REPA REPAIR IR When equipment deterioration has reached a point that the risk of failure cannot be managed to an acceptable level, replacement/repair is often the only way to mitigate the risk.

13.3 EVALUAT EVALUATING ING FLAWS FLAWS FOR FITNESSFITNESS-FOR FOR-SERVICE Inspection may identify flaws in equipment. A fitness-forservice assessment (e.g., API RP 579) may be performed to determine if the equipment may continue to be safely operated, under what conditions and for what time period. A fitness-for-service analysis can also be performed to determine what size flaws, if found in future inspections, would require repair or equipment replacement.

13.4 13. 4 EQUIPM EQUIPMENT ENT MODIFI MODIFICAT CATION ION,, REDESI REDESIGN GN AND RERATING Modification and redesign of equipment can provide mitigation of probability of failure. Examples include: a. Change Change of metall metallur urgy gy.. b. Addition Addition of protective protective linings linings and coatings. coatings. c. Remov Removal al of deadl deadlegs egs.. d. Increased Increased corrosi corrosion on allowan allowance. ce. e. Physical Physical changes changes that will help help to control/m control/minimi inimize ze deterioration. f. Insula Insulatio tion n improv improveme ements nts.. g. Injection Injection point point design design changes. changes. Sometimes equipment is over designed for the process conditions. Rerating the equipment may result in a reduction of the probability of failure assessed for that item.

13.5 13.5 EMER EMERGE GENC NCY Y ISO ISOLA LATI TION ON Emergency isolation capability can reduce toxic, explosion or fire consequences in the event of a release. Proper location of the isolation valves is key to successful risk mitigation. Remote operation is usually required to provide significant risk reduction. To mitigate flammable and explosion risk, operations need to be able to detect the release and actuate the isolation valves quickly (within a few minutes). Longer response times may still mitigate effects of ongoing fires or toxic releases.

EMERGE EMERGENC NCY Y DE DEPRE PRESSU SSURIZ RIZING ING// DE-INVENTORY

13.7 13.7 MODI MODIFY FY PR PROC OCES ESS S Mitigation of the primary source of consequence can be achieved by changing the process towards less hazardous conditions. Examples: a. Reduce temperat temperature ure to below atmospher atmospheric ic pressure pressure boiling point to reduce size of cloud. b. Substitute Substitute a less hazardous hazardous materia materiall (e.g., high flash flash solvent for a low flash solvent). c. Use a continuous continuous process process instead instead of a batch batch operation. operation. d. Dilute Dilute hazardou hazardouss substanc substances. es.

13.8 13.8 RE REDU DUCE CE INVE INVENT NTOR ORY Y This method reduces the magnitude of consequence. Some examples: a. Reduce/elim Reduce/eliminate inate storage storage of hazardous hazardous feedstocks feedstocks or intermediate products. b. Modify Modify process control control to permit a reduction reduction in inventory inventory contained in surge drums, reflux drums or other in-process inventories. c. Select process process operations operations that require less invento inventory/hol ry/holddup. d. Substitute Substitute gas phase phase technology technology for liquid liquid phase. phase.

13.9 13. 9

WATER ATER SPRA SPRAY/ Y/DE DELU LUGE GE

This method can reduce fire damage and minimize or prevent escalation. A properly designed and operating system can greatly reduce the probability that a vessel exposed to fire will BLEVE.

13.1 13.10 0 WATER ATER CU CURT RTAI AIN N Water sprays entrap large amounts of air into a cloud. Water curtains mitigate water soluble vapor clouds by absorption as well as dilution and insoluble vapors (including most flammables) by air dilution. Early activation is required in order to achieve significant risk reduction. The curtain should preferably be between the release location and ignition sources (e.g., furnaces) or locations where people are likely to be present. Design is critical for flammables, since the water curtain can enhance flame speed under some circumstances.

13.11 13. 11 BLASTBLAST-RE RESIS SISTAN TANT T CONST CONSTRU RUCTI CTION ON Utilizing blast resistant construction provides mitigation of the damage caused by explosions and may prevent escalation

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34


of the incident. When used for buildings (see API RP 752), it may provide personnel protection from the effects of an explosion. This may also be useful for equipment critical to emergency response, critical instrument/control lines, etc.

13.12 OTHERS a. Spill Spill detect detectors ors.. b. Steam Steam or air air curtai curtains. ns. c. Fire Firepr proofi oofing ng.. d. Instrumenta Instrumentation tion (interlocks, (interlocks, shut-down shut-down systems, systems, alarms, etc.). e. Inerti Inerting/ ng/gas gas blanketi blanketing. ng. f. Ventilation entilation of buildi buildings ngs and enclosed enclosed structure structures. s. g. Piping Piping redesi redesign. gn. h. Mechanical Mechanical flow restriction. restriction. i. Igniti Ignition on source source control control.. j. Improved Improved design design standar standards. ds. k. Improvemen Improvementt in process safety managemen managementt program. l. Emerg Emergenc ency y eva evacua cuatio tion. n. m. Shelters Shelters (safe havens). havens). n. Toxic scrubbers scrubbers on buildi building ng vents. vents. o. Spill Spill conta containm inment ent.. p. Facili Facility ty siti siting. ng. q. Condit Condition ion monito monitorin ring. g. r. Improved Improved training training and procedures. procedures. ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

14 Reas Reasse sess ssme ment nt and and Upd Updat atin ing g RBI Assessments 14.1 14. 1

RBII RE RB REAS ASSE SESS SSME MENT NTS S

RBI is a dynamic tool that can provide current and pro jected future future risk risk evaluation evaluations. s. However However,, these evaluat evaluations ions are based on data and knowledge at the time of the assessment. As time goes by, changes are inevitable and the results from the RBI assessment should be updated. It is important to maintain and update a RBI program to assure the most recent inspection, process, and maintenance information is included. The results of inspections, changes in process conditions and implementation of maintenance practices can all have significant effects on risk and can trigger the need to perform a reassessment.

14.2 14. 2

WHY WHY CONDU CONDUCT CT A RBI REA REASS SSESS ESSMEN MENT? T?

There are several events that will change risks and make it prudent to conduct a RBI reassessment. It is important important that the facility have an effective management of change process that identifies when a reassessment is necessary. Sections 14.2.1 through 14.2.4 provide guidance on some key factors that could trigger a RBI reassessment.


14.2.1 14. 2.1 Deteri Deteriora oratio tion n Mechanis Mechanisms ms and Inspect Inspection ion Activities Many deterioration mechanisms are time dependent. Typically, the RBI assessment will project deterioration at a continuous rate. In reality, the deterioration rate may vary over time. Through inspection activities, the average rates of deterioration may be better defined. Some deterioration mechanisms are independent of time (i.e., they occur only when there are specific conditions present). These conditions may not have been predicted in the original assessment but may have subsequently occurred. Inspection activities will increase information on the condition of the equipment. When inspection activities have been performed, the results should be reviewed to determine if a RBI reassessment is necessary.

14.2.2 14. 2.2 Proce Process ss and and Hardw Hardware are Chang Changes es Changes in process conditions and hardware changes, such as equipment modifications or replacement, frequently can significantly alter the risks, and dictate the need for a reassessment. Process changes, in particular, particular, have been linked to equipment failure from rapid or unexpected corrosion or cracking. This is particularly important for deterioration deterioration mechanisms that depend heavily on process conditions. Typical examples include chloride stress corrosion cracking of stainless steel, wet H 2S cracking of carbon steel and sour water corrosion. In each case, a change in process conditions can dramatically affect the corrosion rate or cracking tendencies. Hardware changes can also have an effect effect on risk. For example: a. The probability probability of failur failuree can be affected affected by changes changes in the design of internals in a vessel or size and shape of piping systems that accelerate velocity related corrosion effects. b. The consequence consequence of failure failure can be affected affected by the relocarelocation of a vessel to an area near an ignition source.

14.2.3 14. 2.3 RBI Ass Assessm essment ent Premis Premise e Chan Change ge The premises for the RBI assessment could change and have a significant impact on the risk results. Some of the possible changes could be: a. Increase Increase or decrease decrease in population population density density.. b. Change in materials materials and and repair/replac repair/replacement ement costs. costs. c. Change Change in produ product ct value values. s. d. Revisions Revisions in safety safety and environment environmental al laws and regulations. e. Revisions Revisions in the users users risk risk management management plan plan (such as changes in risk criteria).

14.2.4 14. 2.4 The Effe Effect ct of Miti Mitigat gation ion Strateg Strategies ies Strategies to mitigate risks such as installation of safety systems, repairs etc. should be monitored to assure they have



successfully achieved the desired mitigation. Once a mitigation strategy is implemented, a reassessment of the risk may be performed to update the RBI program.

14.3 14. 3 WHEN WHEN TO CONDUC CONDUCT T A RBI RBI REASSE REASSESSM SSMENT ENT 14.3.1 14. 3.1 After After Signifi Significan cantt Change Changes s As discussed in 14.2, significant changes in risk can occur for a variety of reasons. Qualified personnel should evaluate each significant change to determine the potential for a change in risk. It may be desirable to conduct a RBI reassessment after significant changes in process conditions, deterioration mechanisms/rates/severities or RBI premises.

14.3 14.3.2 .2 Afte Afterr a Set Time Time Per Perio iod d Although significant changes may not have occurred, over time many small changes may occur and cumulatively cause significant changes in the RBI assessment. Users should set default maximum time periods for reassessments. The governing inspection codes (such as API 510, 570 and 653) and jurisdicti jurisdictional onal regulat regulations ions should should be reviewed reviewed in in this context. context.

14.3.3 14. 3.3 After After Implem Implement entati ation on of Risk Risk Mitigat Mitigation ion Strategies Once a mitigation strategy is implemented, it is prudent to determine how effective the strategy was in reducing the risk to an acceptable level. level. This should be reflected in a reassessment of the risk and appropriate update in the documentation.

14.3.4 Before Before and After Maintenanc Maintenance e Turnaround urnarounds s As part of the planning before a maintenance turnaround, it could be useful to perform a RBI reassessment. This can become a first step in planning the turnaround to insure the work effort is focused on the higher risk equipment items and on issues that might affect the ability to achieve the premised operating run time in a safe, economic and environmentally sound manner. Since a large amount of inspection, repairs and modifications are performed during a maintenance turnaround, it may be useful to update an assessment after the turnaround to reflect the new risk levels.

15 Roles, Roles, Respons Responsibili ibilities ties,, Training raining and Qualifications 15.1 15.1 TEA EAM M APP APPR ROAC OACH RBI requires data gathering from many sources, specialized analysis, and then risk management decision-making. Generally, one individual does not have the background or skills to single-handedly conduct the entire study. study. Usually, a team of people, with the requisite skills and background, is

needed to conduct an effective RBI assessment. Section 15.2 sets out a listing of a typical RBI team. Depending on the application, some of the disciplines listed may not be required. Some team members may be part-time due to limited input needs. It is also possible that not all the team memmembers listed may be required if other team members have the required skill and knowledge of multiple disciplines. It may be useful to have one of the team members to serve as a facilitator for discussion sessions and team interactions.

15.2 15. 2

TEA EAM M MEMB MEMBER ERS, S, ROLE ROLES S& RESPONSIBILITIES

15.2 15.2.1 .1 Team eam Lead Leader er The team leader may be any one of the below mentioned team members. The team leader should be a full-time team member, and should be a stakeholder in the facility/equipment being analyzed. The team leader typically is responsible for: a. Formation Formation of the the team and verifyi verifying ng that the team team members have the necessary skills and knowledge. b. Assuring Assuring that the study study is conducted conducted properly. properly. 1. Data gath gathere ered d is accurat accurate. e. 2. Assumptions Assumptions made made are logical logical and documente documented. d. 3. Appropriate Appropriate personnel personnel are utilized utilized to provide provide data and assumptions. 4. Appropriate Appropriate quality quality and validity validity checks checks are employed employed on data gathered and on the data analysis. c. Preparing Preparing a report on the RBI study study and distribu distributing ting it to the appropriate personnel whom are either responsible for decisions on managing risks or responsible for implementing actions to mitigate the risks. d. Following Following up to assure assure that the appropriate appropriate risk mitigati mitigation on actions have been implemented.

15.2.2 15. 2.2 Equip Equipmen mentt Inspec Inspector tor or or Inspec Inspectio tion n Specialist The equipment inspector or inspection specialist is generally responsible for gathering data on the condition and history of equipment in the study. study. This condition data should include the new/design new/design condition and current condition. Generally, this information will be located in equipment inspection and maintenance files. If condition data are unavailable, the inspector/specialist, in conjunction with the materials and corrosion specialist, should provide predictions of the current condition. The inspector/specialist and materials & corrosion specialist are also responsible for assessing the effectiveness of past inspections. The equipment inspector/inspection inspector/inspection specialist is usually responsible for implementing the recommended inspection plan derived from the RBI study. --`,,``,,`,,,,,,`,,,`,,````,`,-`-`,,`,,`,`,,`---


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15.2.3 15. 2.3 Materi Materials als and and Corro Corrosio sion n Special Specialist ist The materials and corrosion specialist is responsible for assessing the types of deterioration mechanisms and their applicability and severity to the equipment considering the process conditions, environment, metallurgy, age, etc., of the equipment. This specialist should compare this assessment to the actual condition of the equipment, determine the reason for differences between predicted and actual condition, and then provide guidance on deterioration mechanisms, rates or severity to be used in the RBI study. study. Part of this comparison should include evaluating the appropriateness of the inspections in relation to the deterioration deterioration mechanism. This specialist also should provide recommendations on methods of mitigating the probability of failure (such as changes in metallurgy, addition of inhibition, addition of coatings/linings, etc.) and methods of monitoring the process for possible changes in deterioration rates (such as pH monitoring, corrosion rate monitoring, contaminant monitoring, etc.). ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

15.2. 15. 2.4 4

Proc Proces ess s Speci Special alis istt

The process specialist is responsible for the provision of process condition condition information. information. This information generally will be in the form of process flow sheets. The process specialist is responsible for documenting variations in the process conditions due to normal occurrences (such as start-ups and shutdowns) and abnormal occurrences. The process specialist is responsible for describing the composition and variability of all the process fluids/gases as well as their potential toxicity and flammability. flammability. The process specialist should evalevaluate/recommend methods of risk mitigation (probability or consequence) through changes in process conditions.

15.2.5 15. 2.5 Operat Operation ions s and Mainten Maintenanc ance e Person Personnel nel This person(s) is responsible for verifying that the facility/ equipment is being operated within the parameters set out in the process operating envelope. envelope. They are responsible for providing data on occurrences when the process deviated from the limits of the process operating envelope. envelope. They are also responsible for verifying that equipment repairs/replacements/additions have been included in the equipment condition data supplied by the equipment inspector. Operations and maintenance are responsible for implementing recommendations that pertain to process or equipment modifications and monitoring.

15. 15.2.6 2.6

Mana anagem gement ent

Management’s role is to provide sponsorship and resources (personnel and funding) for the RBI study. study. They are responsible for making decisions on risk management or providing the framework/mechanism for others to make these decisions based on the results of the RBI study. Finally, management is


responsible for providing the resources and follow-up system to implement the risk mitigation decisions.

15.2.7 15. 2.7 Ris Risk k Ass Assessm essment ent Perso Personn nnel el This person(s) is responsible for assembling all of the data and carrying out the RBI analysis. This person(s) is typically responsible for: a. Defining data data required required from from other other team members members.. b. Defining accura accuracy cy levels levels for for the data. data. c. Verifying erifying through quality quality checks checks the soundness soundness of data and assumptions. d. Inputting/t Inputting/transfe ransferring rring data into the computer computer program and running the program (if one is used). e. Quality Quality control control of data data input/ou input/output. tput. f. Manually Manually calculatin calculating g the measures measures of risk risk (if a computer computer program is not used). g. Displaying Displaying the results results in an understandabl understandablee way and preparing appropriate reports on the RBI analysis. Furthermore, this person(s) should be a resource to the team conducting a risk/benefit analysis if it is deemed necessary. necessary.

15.2.8 15. 2.8 Envir Environm onment ental al and Safety Safety Perso Personn nnel el This person(s) is responsible for providing data on environmental and safety systems and regulations. He/she also is is responsible for assessing/recommending ways to mitigate the consequence of failures.

15.2.9 15. 2.9 Financ Financial ial/Bu /Busin siness ess Pers Person onnel nel This person(s) is responsible for providing data on the cost of the facility/equipment being analyzed and the financial impact of having pieces of equipment or the facility shut down. He/she also should recommend methods for mitigating the financial consequence of failure.

15.3 15. 3 TRA RAINI INING NG AND QUALI QUALIFIC FICATI ATIONS ONS FOR FOR RBI APPLICATION 15.3.1 15. 3.1 Ris Risk k Ass Assessm essment ent Perso Personn nnel el This person(s) should have a thorough understanding of risk analysis either by education, training, or experience. He/ she should have received detailed training on the RBI methodology and on the procedures being used for the RBI study so that he/she understands how the program operates and the vital issues that affect the final results. Contractors that provide risk assessment personnel for conducting RBI analysis should have a program of training and be able to document that their personnel are suitably qualified and experienced. Facility owners that have internal risk assessment personnel conduct RBI analysis should have a procedure to document that their personnel are sufficiently



qualified. The qualifications and training of the risk assessment personnel should be documented.

15.3 15.3.2 .2 Othe Otherr Team Mem Membe bers rs The other team members should receive basic training on RBI methodology and on the program(s) being used. This training should be geared primarily to an understanding and effective effective application of RBI. This training could be provided provided by the risk assessment personnel on the RBI Team or by another person knowledgeable on RBI methodology and on the program(s) being used.

16 RBI RBI Docu Docume ment ntat atio ion n and and Reco Record rd-keeping 16.1 GENERAL It is important that sufficient information is captured to fully document the RBI assessment. Typically, Typically, this documentation should include the following data: a. The type type of of assess assessmen ment. t. b. Team members members performing performing the assessmen assessment. t. c. Time Time frame over over which the assessment assessment is applicabl applicable. e. d. The inputs inputs and sources sources used to determin determinee risk. e. Assumptions Assumptions made made during during the the assessment assessment.. f. The risk assessm assessment ent results results (includi (including ng informatio information n on probability and consequence). g. Follow-up Follow-up mitigation mitigation strategy strategy,, if applicable, applicable, to manage risk. h. The mitigated risk levels levels (i.e., residual risk after mitigation mitigation is implemented). i. References References to codes codes or standa standards rds that have have jurisdicti jurisdiction on over extent or frequency of inspection. Ideally, sufficient data should be captured and maintained such that the assessment can be recreated or updated at a later time by others who were not involved in the original assessment. To facilitate this, it is preferable to store the information in a computerized database. This will enhance the analysis, retrieval, retrieval, and stewardship stewardship capabilities. The usefulness of the database will be particularly important in stewarding recommendations developed from the RBI assessment, and managing overall risk over the specified time frame.

16.2 16.2 RB RBII MET METHO HODO DOLO LOGY GY The methodology used to perform the RBI analysis should be documented so that it is clear what type of assessment was performed. The basis for both the probability and consequences of failure failure should be documented. If a specific software program is used to perform the assessment, this also should be documented and maintained. The documentation should be sufficiently complete so that the basis and the logic for the decision making process can be checked or replicated at a later time.

16.3 16.3 RB RBII PER ERSO SONN NNEL EL The assessment of risk will depend on the knowledge, experience and judgment of the personnel or o r team performing the analysis. Therefore, a record of the team members involved should be captured. This will be helpful in understanding the basis for the risk assessment when the analysis is repeated or updated.

16.4 6.4

TIME FR FRAME

The level of risk is usually a function of time. time. This either is as a result of the time dependence of a deterioration mechanism, or simply the potential for changes in the operation of equipment. Therefore, the time frame over which the RBI analysis is applicable should be defined and captured in the final documentation. This will permit permit tracking and management of risk effectively effectively over time.

16.5 16. 5

ASSI AS SIGN GNME MENT NT OF RISK RISK

The various inputs used to assess both the probability and consequence of failure should be captured. This should include, but not be limited to, the following information: a. Basic equipment equipment data data and inspection inspection history history critical critical to the assessment, e.g., operating conditions, materials of construction, service exposure, corrosion rate, inspection history, etc. b. Operative Operative and credible credible deteriorat deterioration ion mechanisms. mechanisms. c. Criteria Criteria used to judge judge the severity severity of each each deterioratio deterioration n mechanism. d. Anticipated Anticipated failure failure mode(s) mode(s) (e.g., leak or rupture) rupture).. e. Key factors factors used used to judge the severity severity of each each failure failure mode. f. Criteria Criteria used to evalu evaluate ate the various various conseque consequence nce categocategories, including safety, health, environmental and financial. g. Risk criteria criteria used to evaluate evaluate the acceptabilit acceptability y of the risks.

16.6 16. 6

ASSUM AS SUMPTI PTIONS ONS MAD MADE E TO ASSESS ASSESS RISK RISK

Risk analysis, by its very nature, requires that certain assumptions be made regarding the nature and extent of equipment deterioration. Moreover, Moreover, the assignment of failure failure mode and the severity of the contemplated event will invariably be based on a variety of assumptions, regardless of whether the analysis is quantitative or qualitative. To underunderstand the basis for the overall risk, it is essential that these factors be captured in the final documentation. Clearly documenting the key assumptions made during the analysis of probability and consequence will greatly enhance the capability to either recreate or update the RBI assessment.

16.7 16. 7

RISK RISK A ASS SSES ESSM SMEN ENT T RESU RESULT LTS S

The probability, consequence and risk results should be captured in the documentation. For items that require risk

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mitigation, the results after mitigation should be documented as well.

sible for implementation of any mitigation should also be documented.

16.8 16. 8

16.9 16. 9 CODES CODES,, STAND STANDAR ARDS DS AND AND GOVER GOVERNME NMENT NT REGULATIONS

MITIGA MITIGATIO TION N AND FOLLO FOLLOW-U W-UP P

One of the most important aspects of managing risk through RBI is the development and use of mitigation strategies. Therefore, the specific risk mitigation required to to reduce either probability or consequence should be documented in the assessment. The mitigation “credit” assigned to a particular action should be captured along with any time dependence. The methodology, process and person(s) respon-


Since various codes, standards and governmental regulations cover the inspection for most pressure equipment, it will be important to reference these documents as part of the RBI assessment. This is particularly particularly important where implementation of RBI is used to reduce either the extent or frequency of inspection. Refer to Section 2 for a listing of some relevant codes and standards.


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APPENDIX A—DETERIORATION MECHANISMS Table able 1—Thinni 1—Thinning ng Deterioration Mechanism

Description

Behavior

Hydrochloric Acid Typically causes localized corrosion in car- Localized Corrosion bon and low alloy steel, particularly at initial condensation points (< 400°F). Austenitic stainless steels experience pitting and crevice corrosion. Nickel alloys can corrode under oxidizing conditions. Galvanic Occurs when two metals are joined and Localized Corrosion exposed to an electrolyte. Ammonia Bisulfide Corrosion

Highly localized metal loss due to erosion corrosion in carbon steel and admiralty brass.

Carbon Dioxide (Carbonic Acid) Corrosion

Carbon dioxide is a weakly acidic gas which Localized is corrosive when dissolved in water becoming carbonic acid (H 2CO3). CO2 is commonly found in upstream sections before treatment. Aqueous CO2 corrosion of carbon and low alloy steels is an electrochemical process involving the anodic dissolution of iron and the cathodic evolution of hydrogen. The reactions are are often accompanied by the formation of films of FeCO 3 (and/or Fe3O4) that can be protective or non-protective depending on the conditions. Very strong acid that causes metal loss in Localized various materials and depends on many factors.

Sulfuric Acid Corrosion

Localized

Key Variables

Acid %, pH, materials Crude unit atmospheric column of construction,temoverhead, Hydrotreating effluent perature trains, Catalytic reforming effluent and regeneration systems.

Joined materials of construction, distance in galvanic series NH4HS % in water (Kp), velocity, pH

Carbon di dioxide co concentration, process conditions.

Acid %, pH, material of construction, temperature, velocity, oxidants Hydrofluoric Acid Very strong acid that causes metal loss in Localized Acid %, pH, material Corrosion various materials. of construction, temperature, velocity, oxidants Phosphoric Acid Weak acid that causes metal loss. Generally Localized Acid %, pH, material Corrosion added for biological corrosion inhibition in of construction, water treatment. temperature Phenol (carbolic Weak organic acid causing corrosion and Localized Acid %, pH, material acid) Corrosion metal loss in various alloys. of construction, temperature Amine Amine Corrosio Corrosion n Used Used in gas treat treatment ment to to remove remove dissol dissolved ved General at low Amine type and conCO2 and H2S acid gases. Corrosion gener- velocities, local- centration, material of ally caused by desorbed acid gases or amine ized at high construction, temperadeterioration products. velocities ture, acid gas loading, velocity Atmospheric The general corrosion process occurring General uniPresence of oxygen, Corrosion under atmospheric conditions where carbon form corrosion temperature range and steel (Fe) is converted to iron oxide Fe 2O3. the availability of water/moisture Corrosion Under Insulation

CUI is a specific case of atmospheric corro- General to sion where the temperatures and the concen- highly trations of water/moisture can be higher. localized Often residual/trace corrosive elements can also be leached out of the insulation material itself creating a more corrosive environment.

Examples

Presence of oxygen, temperature range and the availability of water/moisture and corrosive constituents within the insulation.

Seawater and some cooling water services. Formed by thermal or catalytic cracking in hydrotreating, hydrocracking, coking, catalytic cracking, amine treating and sour water effluent and gas separation systems. Refinery steam condensate system, hydrogen plant and the vapor recovery section of catalytic cracking unit.

Sulfuric acid alkylation units, demineralized water.

Hydrofluoric acid alkylation units, demineralized water.

Water Water treatment plants.

Heavy oil and dewaxing plants.

Amine gas treating units.

This process is readily apparent in high temperature processes where carbon steels have been used without protective coatings (steam piping for example). Insulated piping/vessels.

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Table able 1—Thinn 1—Thinning ing Deterioration Mechanism Soil Soil Corro Corrosi sion on

High Temperature Sulfidic Corrosion without H2

High Temperature Sulfidic Corrosion with H2

Naphthenic Acid Corrosion

Oxida xidattion

Description Meta Metall llic ic str struct ucture uress in conta contact ct with with soil soil will will corrode.

Behavior

Material of construction, soil characteristics, type of coating. A corrosive process similar to atmospheric General uniSulfur concentration corrosion in the presence of oxygen. In this form corrosion and temperature. case the carbon steel (Fe) is converted in the presence of sulfur to iron sulfide (FeS). Conversion rate (and therefore corrosion rate) is dependent on temperature of operation and sulfur concentration. With the presence of hydrogen, a signifiGeneral uniSulfur and hydrogen cantly more aggressive case of sulfidation form corrosion concentration and tem(sulfidic corrosion) can exist. perature.

Naphthenic acid corrosion is attack of steel alloys by organic acids that condense in the range of 350°F to 750°F. The presence of potentially harmful amounts of naphthenic acids in crude may be signified by higher neutralization numbers. A hi high temperature ure cor corro rossion reaction wher here metal is converted to a metal oxide above specific temperatures.

General to localized

Key Variables

Localized corrosion

Examples Tank bottoms, underground piping.

All locations where there is sufficient temperature (450°F minimum) and sulfur is present in quantities greater than 0.2%. Common locations are crude, coker, FCC, and hydroprocessing units.

All locations where there is sufficient temperature (450°F minimum) and sulfur is present in quantities greater than 0.2%. A reas of hydroprocessing units- reactor feed downstream of the hydrogen mix point, the reactor, the reactor effluent and the recycle hydrogen gas including the exchangers, heaters, separators, piping, etc. Naphthenic/organic Middle section of a vacuum column acid concentration and in a crude unit (primarily in the temperature. MVGO cut), can also occur in atmospheric distillation units, furnaces and transfer lines.

General uniTemperature, presence Outside of furnace tubes, furnace form corrosion of air, material of con- tube hangers, and other internal furstruction. nace components exposed to combustion gases containing excess air.

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Table 2—Stress 2—Stress Corrosion Corrosion Cracking Cracking Deterioration Mechanism

Description

Behavior

Chloride Cracking Cracking Cracking Cracking that can initiate initiate from the ID Transgranular or OD of austenitic stainless steel cracking. equipment, primarily due to fabrication or residual stresses. Some applied stresses can also cause cracking.

Key Variables

Examples

Externally present in equipment with poor insulation and weatherproofing, downwind of cooling water spray and equipment exposed to fire water. Internally wherever chlorides can be present with water such as atmospheric column overheads of crude units and reactor effluent condensing streams. Caustic Caustic Crac Cracking king Cracking Cracking prim primari arily ly initia initiated ted from from the the Typically, inter- Caustic concentration, pH, Caustic treating sections, caustic serID of carbon steel equipment, prima- granular, also material of construction, vice, mercaptan treatment, crude rily due to fabrication or residual can be transtemperature, stress. unit feed preheat desalting, sour stresses. granular crackwater treatment, steam systems. ing. Polythionic Acid Cracking of austenitic stainless steels Intergranular Material of construction, Generally occurs in austenitic stainCracking in the sensitized condition (due to high cracking. sensitized microstructure, less steel materials in catalytic cracktemperature exposure or welding) in presence of water, polying unit reactor and flue gas systems, the presence of polythionic acid in wet, thionic acid. desulfurizer furnaces and hydroproambient conditions. Polythionic acid cessing units. is formed by a conversion of FeS in the presence of water and oxygen. Amine Amine Crac Cracki king ng Amin Aminee is use used d in gas gas trea treatm tmen entt to Intergranular Amine type and concentra- Amine treating units. remove dissolved CO2 and H2S acid cracking. tion, material of construcgases. Cracking generally caused by tion, temperature, stress. desorbed acid gases or amine deterioration products. Ammonia Cracking of carbon steel and admiralty Intergranular Material of construction, Generally present in ammonia proCracking brass. cracking in car- temperature, stress. duction and handling such as overbon steel, transhead condensation where ammonia granular in is a neutralizer. copper zinc alloys. Hydrogen Induced Occurs in carbon and low alloy steel Planar cracks H2S concentration, water, Anywhere that H2S is present with Cracking / Stress materials in the presence of water and (blisters), temperature, pH, material water such as crude units, catalytic Oriented HydroH2S. Deterioration of the material Transgranular of construction. cracking compression and gas recovgen Induced properties is caused when atomic cracks as blisery, hydroprocessing, sour water and Cracking ters progress hydrogen, generated through corrocoker units. sion, diffuses into the material and toward welds. reacts with other atomic hydrogen to form molecular hydrogen gas in inclusions of the steel. Deterioration can take the form of blisters and step-wise cracking in stress relieved equipment and non-stress relieved equipment. Sulfide Stress Occurs in carbon and low alloy steel Transgranular H2S concentration, water, Anywhere that H2S is present with Cracking materials in the presence of water and cracking, nor- temperature, pH, material water such as crude units, catalytic H2S. Deterioration takes the form of mally associof construction, post weld cracking compression and gas recovcracking in non or improperly stress ated with heat treatment condition, ery, hydroprocessing, sour water and relieved equipment. fabrication, hardness coker units. attachment and repair welds.


Acid (chloride) concentration, pH, material of construction, temperature, fabrication, stresses approaching yield.


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Table 2—Stress 2—Stress Corrosion Corrosion Cracking Cracking Deterioration Mechanism Hydrogen Blistering

Description

Occurs in carbon and low alloy steel materials in the presence of water and H2S. Deterioration of the material properties is caused by atomic hydrogen generated through corrosion diffuses into the material and reacts with other atomic hydrogen to form molecular hydrogen gas in inclusions of the steel. Deterioration takes the form of planar blisters and can occur in stress relieved and non-stress relieved equipment. Hydrogen Presence if hydrogen cyanide can proCyanide Cracking mote hydrogen deterioration (SOHIC, SCC, and blistering) by destabilizing the iron sulfide protective surface scale. ` , , ` ` , , ` , , , , , , ` , , , ` , , ` ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -


Behavior

Key Variables

Examples

Planar cracks (blisters).

H2S concentration, water, temperature, pH, material of construction.

Anywhere that H2S is present with water such as crude units, catalytic cracking compression and gas recovery, hydroprocessing, sour water and coker units.

Planar cracks (blisters) and transgranular cracking.

Presence of HCN, H 2S con- Anywhere that H2S is present with centration, water, tempera- water such as crude units, catalytic ture, pH, material of cracking compression and gas recovconstruction. ery, hydroprocessing, sour water and coker units.



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Table 3—Metallurgical 3—Metallurgical and Environmental Environmental Failures Failures Deterioration Mechanism High-Temperature Hydrogen Attack

Description

Occurs in carbon and low alloy steel materials in the presence of high temperature and hydrogen, usually as a part of the hydrocarbon stream. At elevated temperatures (> 500°F), deterioration of the material properties is caused by methane gas forming fissures along the grain boundaries. Atomic hydrogen diffuses into the material and reacts with carbon from the steel, forming methane gas and depleting the steel of carbon. Grain Growth Occurs when steels are heated above a certain temperature, beginning about 1100°F for CS and most pronounced at 1350°F. Austenitic stainless steels and high nickelchromium alloys do not become subject to grain growth until heated to above 1650°F. Graphitization Occurs when the normal pearlite grains in steels decompose into soft weak ferrite grains and graphite nodules usually due to long term exposure in the 825°F–1400°F range. Sigma Phase Occurs when austenitic and other Embrittlement stainless steels with more than 17% chromium are held in the range of 1000°F–1500°F for extended time periods. 885°F 885°F Embri Embrittl ttleme ement nt Occurs Occurs after after aging aging of ferrit ferritee concontaining stainless steels at 650°F– 1000°F and produces a loss of ambient temperature ductility. Temper Temper Embritt Embrittlement lement Occurs when low low alloy alloy steels steels are held for long periods of time in temperature range of 700°F–1050°F. There is a loss of toughness that is not evident at operating temperature but rather shows up at ambient temperature and can result in brittle fracture.

Liquid Metal Embrittlement


Behavior

Key Variables

Examples

Intergranular fissure cracking, decarburization.

Material of construction, hydrogen partial pressure, temperature, time in service.

Typically occurs in reaction sections of hydrocarbon processing units such as hydrodesulfurizers, hydrocrackers, hydroforming and hydrogen production units.

Localized

Maximum temperature reached, time at maximum temperature, material of construction.

Furnace tubes failures, fire damaged equipment, equipment susceptible to run-away reactions.

Localized

Material of of co construction, temperature and time of exposure.

FCC reactor.

General ralized

Material of const nstruct uction, on, temperature and time of exposure.

Cast furnace tubes and components, regenerator cyclones in FCC unit.

General ralized

Material of const nstruct uction, on, temperature.

Cracking of wrought and cast steels during shutdowns.

General ralized

Material of const nstruct uction, on, temperature and time of exposure.

During shutdown and start-up conditions the problem may appear for equipment in older refinery units that have operated long enough for this condition to develop. Hydrotreating and hydrocracking units are of interest because they are used at elevated temperatures. Mercury is found in some crude oils and subsequent refinery distillation can condense and concentrate it at low spots in equipment such as condenser shells. Failure of process instruments that utilize mercury has been known to introduce the liquid metal into refinery streams.

Form of catastrophic brittle failure Localized of a normally ductile metal caused when it is in, or has been in, contact with a liquid metal and is stressed in tension. Examples include stainless steel and zinc combination and copper based alloys and mercury combination.

Material of of co construction, tension stress, presence of liquid metal.


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Table 3—Metallurgica 3—Metallurgicall and Environmental Environmental Failures Failures Deterioration Mechanism Carburization

Decarbur rburiization

Metal Du Dusting

Sele Select ctiv ivee Leac Leachi hing ng

Description

Behavior

Caused by carbon diffusion into the Localized steel at elevated temperatures. The increased carbon content results in an increase in the hardenability of ferritic steels and some stainless steels. When carburized steel is cooled a brittle structure can result. Loss oss of of ca carbon rbon from from the surfa rface of of a Localized ferrous alloy as a result of heating h eating in a medium that reacts with carbon. Highly lo localized ca carburization an and Localized subsequent wastage of steels exposed to mixtures of hydrogen, methane, CO, CO 2, and light hydrocarbons in the temperature range of 900°F–1500°F. Prefe Prefere rent ntia iall loss loss of one allo alloy y phase phase Localized in a multiphase alloy.

Key Variables

Examples

Material of of co construction, temperature and time of exposure.

Furnace tubes having coke deposits are a good candidate for carburization (ID).

Material of of co construction, temperature environment.

Carbon steel furnace tubes (OD). Result of excessive overheating (fire). Dehydrogenation units, fired heaters, coker heaters, cracking units and gas turbines.

Temperature, pr process stream composition.

Process stream flow condi- Admiralty tubes used in cooltions, material of construc- ing water systems. tion.

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Table 4—Mechanical 4—Mechanical Failures Failures Deterioration Mechanism

Description

Behavior

Mecha Mechanic nical al Fati Fatigue gue

Fail Failure ure of a comp compone onent nt by crac cracki king ng Loca Locallized ized after the continued application of cyclic stress which exceeds the material’s endurance limit.

Corr Corros osio ion n Fat Fatig igue ue

Form Form of fati fatigu guee wher wheree a corr corros osio ion n process, typically pitting corrosion adds or promotes the mechanical fatigue process. Caused by the rapid formation and collapse of vapor bubbles in liquid at a metal surface as a result of pressure variations. Typical examples are th e misuse of tools and equipment, wind deterioration, careless handling when equipment is moved or erected. Occurs when loads in ex excess of th the maximum permitted by design are applied to equipment.

Cavitation

Mechanical Deterioration

Overloading

Localized

N/A

Equipment design, operat- Flange faces and other machined ing procedures. seating surfaces may be damaged when not protected with covers or when not handled with care. Equipment design, operat- Hydrostatic testing can overload ing procedures. supporting structures due to excess weight applied. Thermal expansion and contraction can cause overloading problems. Equipment design, operat- Excess heat as a result of upset ing procedures. process condition can result in over-pressuring; blocking off equipment which is not designed to handle full process pressure. Materia rial of of con const stru rucction, During equipment pressurization temperature. in absence of precautionary measures. Materia rial of of con const stru rucction, Furnace tubes and supports. temperature, applied stress.

N/A

Bri Brittle Fra Fraccture ure

Loss oss of of du ductility wh wherein the the steel is is referred to as having low notch toughness or poor impact strength. High temperature mechanism wherein continuous plastic deformation of a metal takes place while under stresses below the normal yield strength. Time to fa failure for a metal at elevated temperatures under applied stress below its normal yield strength. Occurs urs whe when large and nonnon-u unif niform orm thermal stresses develop over a relatively short time in a piece of equipment due to differential expansion or contraction. If movement of the equipment is restrained this can produce stresses above the yield strength of the material. Thermal fa fatigue is a proc rocess of of cyclic changes in stress in a material due to cyclic change in temperature.

Ther hermal Shoc Shock k

Ther hermal Fa Fatigue

Cyc Cyclic lic stre stress ss level, el, mate materi rial al Reciprocating parts in pumps and of construction. compressors and the shafts of rotating machinery and associated piping, cyclic equipment such as pressure swing absorbers. Cycl yclic st stress, ma materia rial of of Steam drum headers, boiler tubes. construction, pitting potential of the process stream. Pressure ure head value along ong Backside of pump impellers, the flow of process stream. elbows.

Appl Appliicati cation on of pres pressu sure re in exce xcess of N/A the maximum allowable working pressure of the equipment under consideration.

Stress Rupture

Examples

Localized

Over Over-p -pre ress ssur urin ing g

Creep

Key Variables

Localized

Localized

Localized

Materia rial of of con const stru rucction, Furnace tubes. temperature, applied stress, time of exposure.

Localized

Equi quipme pment design, opera peratt- Associated with occasional, brief ing procedures. flow interruptions or during a fire.

Localized

Equi quipme pment design, opera peratt- Coke drums are subject to thermal ing procedures. cycling and associated thermal fatigue cracking. Bypass valves and piping with heavy weld reinforcement on reactors in cyclic temperature service are also prone to thermal fatigue.

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API RP 575 Inspection of Atmospheric an Low-Pressure Storage Tanks

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