STP-PT-048 CRITERIA FOR RELIABILITY-BASED DESIGN AND ASSESSMENT FOR ASME B31.8 CODE Prepared by: Maher Nessim C-FER Technologies -N)ME STANDARDS TECHNOLOGY, llC Date oflssuance: June 30, 2012 This report was prepared as an account of work sponsored by ASME Pressure Technologies Codes and Standards and the ASME Standards Technology, LLC (ASME ST-LLC) Neither ASME, ASME ST-LLC, the author, nor others involved in the preparation or review of this report, nor any of their respective employees, members or persons acting on their behalf, makes any warranty, express or imp! ied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe upon privately owned r ights Reference herein to any specific commercial product, process or service by trade name, trademark, manufacturer or otherwise does not necessarily constitute or imply its endorsement, recommendation or favoring by ASME ST-LLC or others involved in the preparation or review of this report, or any agency thereof The views and opinions of the authors, contributors and reviewers of the report expressed herein not necessarily reflect those of ASME ST-LLC or others involved in the preparation or review of this report, or any agency thereof ASME ST-LLC does not take any position with respect to the validity of any patent rights asserted in connection with any items mentioned in this document, and does not undertake to insure anyone utilizing a publication against liability for infringement of any applicable Letters Patent, nor assumes any such liability Users of a publication are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility Participation by federal agency representative(s) or person(s) affiliated with industry is not to be interpreted as government or industry endorsement of this publication ASME is the registered trademark of the American Society of Mechanical Engineers No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher ASME Standards Technology, LLC Three Park Avenue, New York, NY 10016-5990 ISBN No 978-0-79 18-3365-0 Copyright © 20 12 by ASME Standards Technology, LLC All Rights Reserved Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code STP-PT-048 TABLE OF CONTENTS FORWORD vi l PURPOSE l SCOPE 3 DEFINITIONS 4 OVERVIEW OF RBDA METHODOLOGY 4.1 Implementation Steps 4.2 Reliability and Failure Probability 4.3 Failure Probability versus Failure Rate 4.4 Time Dependence and Effect of Maintenance I LIMIT STATES l2 5.1 Limit State Categories 12 5.2 Applicable Limit States 13 RELIABILITY TARGETS 17 6.1 General 17 6.2 Ultimate Limit State Targets 20 6.3 Leakage Limit States 38 6.4 Serviceability Limit States 40 6.5 Operational Issues 41 DEVELOPING A LIMlT STATE FUNCTION 42 PROBALISTIC CHARACTERIZATlON OF INPUT VARIABLES 43 RELIABILITY ESTIMATION 44 10 IMPLICATIONS OF USING THE APPENDIX 45 10.1 Design of New Pipelines .45 10.2 Maintenance of Operating Pipelines .47 11 EXAMPLEAPPLICATIONS 51 11 New Pipeline Design 51 11.2 Class Upgrade Deferral 54 12 REFERENCES 58 Acknowledgments 60 lll STP-PT-048 Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code LIST OF FIGURES Figure l - Steps Involved in lmplemeting RBDA Figure 2- Illustration of Load Effect and Resistance Distributions Figure 3- Illustration of Time Dependence and Effect of Maintenance on Reliablity II Figure - Illustration of the Evaluation Length 18 Figure - Reliablity Targets for Ultimate Limit States 23 Figure 6- Risk as a Function of pPD3 for a Range of Design Cases 25 Figure - Example Population Density Plot 26 Figure 8- Relative Frequency of Unpopulated Areas Around Pipelines 27 Figure -A Possible Segmentation Scheme for the Example in Figure 28 Figure 10- Calculation of the Population Density at a Point Along the Pipeline 29 Figure 11 - Ulustration of the Method of Calculating pi 30 Figure 12- Example Illustrating the Calculation of a Population Density Graph 31 Figure 13 - Ulustration of Distributed and Location-specific Limit States 34 Figure 14- Ulustration of Location-specific Limit States Around a Given Point 35 Figure 15- Reported Defect Locations and Governing Evaluation Lengths 36 Figure 16 - Calculated Equivalent Rupture Reliability for the General Reliability Check 37 Figure 17 - Calculated Equivalent Rupture Reliability for the Location-specific Reliability Checks 38 Figure 18- Peak Small Leak Rates for the Design Cases as a Function of Wall Thickness 40 Figure 19 - Design Factor Comparison Between for RBDA and ASME B31.8 46 Figure 20- Cost Comparison Between RBDA and ASME B3L8 Designs 47 Figure 21 -Comparison between Failure Rates for RBDA and Current Practice 49 Figure 22 - Calculated ULS Reliability versus Target for Segment B 53 Figure 23 -Calculated LLS Reliability versus Target for Segment B 53 Figure 24- LLS Reliability Compared to Target for Status Quo 55 Figure 25 - LLS Reliability Compared to Target for Status Quo 56 Figure 26- ULS Reliability Compared to Target for Various Class Upgrade Options 57 IV Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code STP-PT-048 LIST OF TABLES Table l -List of Applicable Limjt States 51 Table 2- Population Density and Reliability Targets for Each Pipeline Segment 51 Table -Equipment Impact Prevention Measures Assumed for Design Example 52 Table 4- Wall Thickness and Equivalent Design Factors 54 Table 5- Basic and Enhanced Failure Prevention Measures for Equipment lmpact 55 v STP-PT-048 Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code FORWORD This Criteria Document provides guidance to potential users of the proposed ASME Appendix B3 I 8R on Reliability Based Design and Assessment (RBDA) by documenting the relevant background information required to fully understand the requirements of the Appendix and to apply them correctly in decision making The need for a Criteria Document was identified during the process of voting on ASME B31.8 Ballot No 08-905 as a requirement for further consideration of the RBDA Appendix Established in 1880, the American Society of Mechanical Engineers (ASME) is a professional not-forprofit organization with more than 127,000 members promoting the art, science and practice of mechanical and multidisciplinary engineering and allied sciences ASME develops codes and standards that enhance public safety, and provides lifelong learning and technical exchange opportunities benefiting the engineering and technology community Visit www.asme.org for more information The ASME Standards Technology, LLC (ASME ST-LLC) is a not-for-profit Limited Liability Company, with ASME as the sole member, formed in 2004 to carry out work related to newly commercialized technology The ASME ST-LLC mission includes meeting the needs of industry and government by providing new standards-related products and services, which advance the application of emerging and newly commercialized science and technology and providing the research and technology development Visit needed to establish and maintain the technical relevance of codes and standards www.stllc.asme.org for more information VI Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code STP-PT-048 PURPOSE This Criteria Document provides guidance to potential users of the proposed ASME Appendix B31.8R on Reliability Based Design and Assessment (RBDA) by documenting the relevant background information required to fully understand the requirements of the Appendix and to apply them conectly in decision making The need for a Criteria Document was identified during the process of voting on ASME B31 Ballot No 08-905 as a requirement for further consideration of the RBDA Appendix The Appendix provides requirements for the application of reliability-based methods to the design and assessment of non-sour natural gas transmission pipelines The Appendix is non-mandatory; however, Section Rl.l in the Appendix states that " if an operator chooses to use the Appendix for designing and operating a pipeline, he must follow it until a different basis fo r pipeline opera tion is established with the r egulator." The reason for this requirement is that the RBDA approach forming the basis for the Appendix permits certain tradeoffs between initial design and planned maintenance (see Section 4.4) For example, the reliability targets may be met by using a thinner wall than would be required by the conventional design approach, combined with a more stringent integrity maintenance plan The Appendix requires that the maintenance plan used to justify the thinner wall be followed and documented to ensure that the reliability targets are met throughout the operational life lt is therefore essential to review and establish a new comprehensive basis for continued operation in cases where thi s requirement is elimill1ated by discontinued compliance with the Appendix The Appendix states that " r elia bility-based methods are particularly useful for pipelines involving large uncertainties application of new materials a nd technologies, unique loading situations, and severe failure conse quences." This statement is based on two key features of the RBDA methodology: ] RBDA is a rigorous methodology While conventional design methods are mostly empirical, RBDA evaluates various design or operational choices from first principles For example, the design factor used for wall thickness selection in conventional standards is a single safety control parameter that is used to design against a combination of threats and is assigned a single value for a range of pipe properties (i.e., diameter, grade, pressure and class) The design factor has been validated through use over the past few decades and therefore its effectiveness is established for pipeline parameters that were commonly used during that period However, it is not necessarily adequate for pipelines made of high strength steels for which little experience exists By contrast, RBDA addr,e sses individual threats based on the actual structural behaviour of the pipe as derived from basic pipe properties For example, equipment impact resistance is evaluated from a model that compares the applied pressure to the pressure required to fai l a gouged dent caused by an excavator hit This model uses the actual pipe parameters, such as diameter, wall thickness and steel grade, and can therefore be applied to the entire range of properties for which it is validated (e.g., higher strength steels) without the need for proof based on prior use The same logic applies for unique loading conditions such as geotechnical loads RBDA explicitly acknowledges uncertainty Safety of possible design or operational alternatives is measured by reliability ( l.Ominus the failure probability) This measure explicitly incorporates the impact of uncertainty A larger degree of uncertainty regarding pipeline behaviour or performance results in a lower calculated level of reliability and a requirement to make more conservative decisions in order to ensure adequate reliability As such, one of the built-in features of the RBDA methodology is the ability to reflect the degree of uncertainty in the decisions made Other key benefits of the RBDA approach include the ability to achieve consistent safety for all pipelines This eliminates unnecessary conservatism in individual cases, allowing more effective use of resources to The Appendix is not applicable to offshore gas transmission pipelines covered by Chapter VIII, or sour gas service covered by Chapter IX, of ASME Standard B31.8 STP-PT-048 Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code achieve better overall safety The methodology also permits integration of design and operational decisions to develop more cost-effective overall solutions The Appendix in its entirety is explicitly applicable to onshore pipelines transporting non-sour lean natural gas This statement is not intended to convey that any of the content is inapplicable to other types of pipelines, but rather that there are certain aspects of the document that are specific to non-sour lean natural gas pipelines Specifically, " the reliability targets in Section R1.6 are based on a model that evaluates the consequences of an ignited lean natural gas release at pressures consistent with the assumption of ideal ga.s behaviour." These targets should therefore not be used directly for other gas compositions or ultra-high pressures that may have significantly different release consequences than those of lean natural gas For rich gas (depending on the particular composition), it may be possible to demonstrate that the underlying release consequence model just mentioned is applicable, and in such cases, the targets can be applied directly If the model does not apply directly, the Appendix may be used with case-specific reliability targets that meet the risk criteria underlying the Appendix Such targets can be developed by adjusting the targets in the Appendix based on the relative magnitude of the release consequences associated with the rich gas composition and/or ultra-high pressure (as calculated from a suitable model) and those calculated from the model underlying the Appendix for the same pipeline Details of this process can be inferred from the original methodology used in developing the reliability targets in the Appendix (Nessim et al.) [1 ], [2] It may also be possible to extend applicability of the Appendix to other fluids, such as sour gas, by making similar adjustments to the reliability targets, as long as the release consequences associated with these fluids are dominated by human safety considerations Apart from the reliability targets and the specific procedure used in demonstrating compliance with them, much of the content of the Appendix is applicable to a wide variety of pipelines This includes all requirements and other information related to the calculation of reliability with respect to different integrity threats Users are advised " to consult the Commentary and the reference material that support the provisions of this Appendix to ensure that the parameters to be used in the design are within the range of applicability of the consequence models used for reliability target calibration." The targets were developed based on a safety benchmark that was calculated from a set of pipeline designs represented by different combinations of diameter, pressure, grade and class location (Nessim et al.) [1], [2] As required by the calibration approach, these cases were selected to cover the range of pipeline parameters that existed at the time of target development The calculation involved use of a specific consequence model, which is built into the targets The intent is to state that if use of the Appendix is considered for pipelines that have design parameters outside the range of the test cases used in the calibration, a check must be carried out to ensure that the consequence model used in the calibration can be reasonably applied to these pipelines The intent is not to impose a limitation on the application of the targets for pipelines that are outside the range defined by the test cases, as long as the consequence model is shown to apply For example, the test cases used in target calibration covered a pressure range of 600 to 1400 psig (4.16 to 9.66 MPa) To apply the targets to a pipeline that has an internal pressure of 1500 psig (1 0.35 MPa), the user should ensure that the release consequence model is applicable to a pipeline operating at 1500 psig (l 0.35 MPa) If this is the case, then the targets can be used for the pipeline even though the pressure is outside the range of pressures considered in the test cases used in the target calibration The restriction described in the previous paragraph does not apply to probability models because failure probabilities must be calculated explicitly The only requirement in that regard is that the probability model used must be appropriate for the pipeline being considered Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code STP-PT-048 SCOPE The ASME B31.8R RBDA Appendix consists of two main sections: Section Rl.O- Requirements: This section states all requirements associated with the application of the RBDA approach, including the reliability targets and the process that must be followed to demonstrate compliance with them It also includes a set of requirements that specify the essential characteristics of a valid reliability estimation approach, but leaves it up to the user to select specific calculation models and procedures Section R2.0 - Commentary: This section provides supplementary technical information to assist the user in applying the Appendix It contains background information on the approach that was used to develop the reliability targets and provides more detailed information on the reliability calculation models and input data While some overlap may exist between tlus document and the Commentary Section (Section R2.0) of the Appendix, the two documents have distinct purposes The Commentary Section R2.0 provides additional technical information to assist users in carrying out the calculations and implementing the procedures required to apply the Appendix This document provides additional information on the rationale behind the requirements and the implications of using them The outline of this Criteria Document is identical to the outline of the Requirements Section of the Appendix (Section Rl.O) For each section, the Criteria Document provides additional information in some or all of the following areas (as applicable) I Explanation of the intent and rationale behind the Requirements (e.g., why the Appendix includes separate reliability targets for location-specific threats such as known corrosion features) Description of key concepts (e.g., definition of the "evaluation length" or the "evaluation period" and why these concepts are required) Elaboration on the underlying concepts (e.g., differences in the types of decisions made and information required when the Appendix is applied to new versus existing pipelines) Presentation of relevant background information (e.g., basic reliability concepts and definitions) Explanation of deviations from previous work (e.g., an explanation of why the document does not treat fatigue and accidental loading as separate limit state types) Presentation of illustrative examples for unique or unfamiliar requirements (e.g., an example of pipeline segmentation based on population density using the minimum population density calculated from two different evaluation lengths) Discussion of the impact ofusing RBDA as compared to conventional design methods (e.g., a description of the impact of using the reliability targets on the relative safety levels for different pipelines) Explanation ofjudgment-based provisions (e.g., why the minimum evaluation length is set to mile or 1600 m) Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code Cl~ss 1600 ] g - - 1200 - 1000 - al a:: ,., "'" BOO I 1600 I :i 1400 psig _ I I ] I 0 1000psig • S.in dia .:t::: c ns I r1-1 OE-04 Q) I I ~- 0:: ~ ~- 1-1 I I I + 1-1 0E-03 2005 t .: -t 2010 Status Quo ll - ~ I -i r -t L, t -J - " II I Class 2-Target ~ -I c:::': I - I "t ~ , r- 2015 ~~ 2020 Li 2025 2030 Year Figure 25 - LLS Re liability Compared to Target for Status Quo The reliability levels associated with different class upgrade options are shown in Figure 26 These options were defined as follows • Replacement Use the same grade (X52 or 358 MPa) and increase the wall thickness from 0.358 to0.401 inches (9 l to 10.2mm) • Pressure reduction Reduce operating pressure from 1000 to 900 psig (6.90 to 6.21 MPa) • Enhanced maintenance For corrosion, carry out more frequent inspections (years 2008, 2013, 2019 and 2027) and increase the minimum safety factor used in initiating repairs from 1.25 to 1.30 For equipment impact, use the enhanced prevention methods in column ofTable Figure 26 shows that the enhanced maintenance option is the only one that meets the reliability target for ULS Pressure reduction and replacement not meet the target, even though they meet the code requirement and have higher costs The reason for this is that the failure probability is dominated by equipment impact, which is more effectively reduced by reducing the hit frequency (see Table 4) than by increasing resistance to hits This demonstrates a situation in which use of the RBDA methodology results in a safer and more cost-effective solution It is noted that reliability has a local peak after each maintenance event, which reflects the reliability improvements associated with the repairs made Figure 26 shows that the reliability at these peaks decreases with time for the pressure reduction option and increases with time for the enhanced maintenance option The trend associated with those peaks reflects the relative magnitude between the reliability improvements resulting from the repairs carried out and the reliability reductions caused by the initiation and growth of new defects The trends observed in the figure are consistent with the fact that the enhanced maintenance option involves more frequent inspections and more stringent repair criteria than the pressure reduction option 56 Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code 1-1 E-06 1-1.0E-05 -E 1-1.0E-04 ~ Q Q) 0::: i l -:1 rl-. -: ll-. -.11-. -:11 :1 -.-J :1 :-1 :1 :-1 :-1 :-1 :-J :-1 -:-1 :-1 :-1 , , -r r ~ ~ -= ===::::-: -F- ~ ~~=F~~~-,_,~F=~F=~+-~~~~=$=$~= - ~~~~~~~~~~~~~~iF~~ / : C'O 1-1.0E-03 STP-PT-048 ~- - - ·Class 1-Target - - ·Class 2-Target - - Enhanced Maintenance - - Replacement - - Pressure Reduction == 1-1.0E-02 + =- - - - - - -= ,r -=- - - , - - - - - - - - - - - - - r - - = , 2005 2010 2015 2020 2025 2030 Year Figure 26 - ULS Reliability Compared to Target for Various Class Upgrade Options 57 STP-PT-048 Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code 12 REFERENCES [1} M Nessim, W Zhou, J Zhou and B Rothwell, Reliability Based Design and Assessment for Location specific Failure Threats with Application to Natural Gas Pipelines, J Pressure Vessel Technology, Vol 131, No.4, Paper No 041701 , Aug 2009 [2} M Nessim, W Zhou, J Zhou and B Rothwell, Target Reliability Levels for Design and Assessment of Onshore Natural Gas Pipelines, J Pre ssure Vessel Technology, Vol 131, No 6, PaperNo 061701 , Dec 2009 [3} J Benjamin and C Cornell, Probability, Statistics and Decision for Civil Engineers, McGraw-Hill, 1970 [4} Offshore Standard DNV-OS-FlOl , Submarine Pipeline Systems, Det Norske Veritas Classification NS, 2007 [5} ISO 16708:2006, Petrolewn and Natural Gas Industries - Pipeline Transportation Systems Reliability-based Limit State Methods, International Organization for Standardization, 2006 [6} M Nessim and W Zhou, Guidelines for Reliability Based Design and Assessment of Onshore Natural Gas Pipelines, GRI Report No GRI-04/0229, 2005a [7] Institute of Gas Engineers, Steel Pipelines for High Pressure Gas Transmission, Recommendations on Transmission and Distribution Practice, IGE/TD/ 4th ed., Communication 1670, London, 200 I [8} M Nessim and W Zhou, Target Reliability Levels for the Design Assessment of Onshore Natural Gas Pipelines, GRI Report No GRI-04/0230, 2005b [9] Reducing Risk, Protecting People, HSE's Decision-making Process, Health and Safety Executive, London, 2001 [10} Land Use Guidelines for Pipeline Corridors, Major Industrial Accidents Council of Canada, Ottawa, Ont , 1995 [11} ASME B31.8S, Managing System Integrity of Gas Pipelines: Supplement to ASME B31.8, American Society of Mechanical Engineers, New York, 2010 [12] CFR 49 Part 192, Transportation of Natural and Other Gas by Pipeline: Minimum Federal Safety Standards Code of Federal Regulations, [current as of 2010 Apr 28] http://ccfr gpoacccss.gov/ cgi/ t/tcxt/text-idx?c=ccfr&sid=c69613dc6ab 940da50340 I db24dc45e7 &rgn=div5&view=text&node=49:3.1.1 1.4&idno=49 [13} M.Stephens, K Leewis and D Moore, A Model for Sizing High Consequence Areas Associated with Natural Gas Pipelines, Proc IPC02, Paper No IPC02-27073 , Calgary, Alberta, Sept 2002 [14} M Stephens, M Nessim and A van Roodselaar, Reliability Based Corrosion ManagementThe Impact of Maintenance and ImpIications for the Time to Next Inspection, Proc IPC20 I 0, 8th International Pipeline Conference, Paper No [PC2010-31399, Calgary, Alberta, Sept 2010 [15] J Kiefner, R Mesloh and B Kiefner, Analysis of DOT Reportable Incidents for Gas Transmission and Gathering System Pipelines, 1985 through 1997, Pipeline Research Council International, Inc., Cat No L51830e, Mar 2001 58 and Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code STP-PT-048 [16} CAN/CSA-S473-04 (S2009), Steel Structures, Forming Part of the Code for the Design, Construction and Installation of Fixed Offshore Structures, Canadian Standards Association, Mississauga, Ont., 2004 [17} M Nessim, H Yue and J Zhou, Application of Reliability Based Design and Assessment to Maintenance and Protection Decisions for Natural Gas Pipelines, Proc IPC20 I 0, 8th International Pipeline Conference, Paper No IPC20 10-31555, Calgary, Alberta, Sept 2010 [18} ASME B31G-2009, Manual for Determining the Remaining Strength of Corroded Pipelines: A Supplement to ASME B31 Code for Pressure Piping, American Society of Mechanical Engineers, New York, 2009 [19} CSA-Z662-07, Oil and Gas Pipeline Systems, Canadian Standards Association, 5th ed., Mississauga, Ont., 2007 59 STP-PT-048 Criteria for Reliability-Based Design and Assessment for ASME B31.8 Code ACKNOWLEDGMENTS The author would like to thank Mark Stephens, MSc, PEng for his technical and editorial review of this document The author further acknowledges, with deep appreciation, the activities of ASME ST-LLC and ASME staff and volunteers who have provided valuable technical input, advice and assistance with review of, commenting on, and editing of, this document 60 ISBN 978-0-7918-3365-0 780791 833650 1111111111111111111111111111111111111111