Stress Corrosion Cracking Recommended Practices
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Stress Corrosion Cracking RReeccoommmmeennddeedd PPrraaccttiicceess,, 22nndd EEddiittiioonn AAnn iinndduussttrryy lleeaaddiinngg ddooccuummeenntt ddeettaaiilliinngg tthhee mmaannaaggeemmeenntt ooff ttrraannssggrraannuullaarr SSCCCC December 2007 Notice of Copyright Copyright © 2007 Canadian Energy Pipeline Association (CEPA). All rights reserved. Canadian Energy Pipeline Association and the CEPA logo are trademarks and/or registered trademarks of Canadian Energy Pipeline Association. The trademarks or service marks of all other products or services mentioned in this document are identified respectively. 1860, 205 – 5 Avenue SW phone: (403) 221-8777 Calgary, Alberta fax: (403) 221-8760 CANADA T2P 2V7 web: www.cepa.com Disclaimer of Liability iii Disclaimer of Liability The Canadian Energy Pipeline Association (CEPA) is a voluntary, non-profit industry association representing major Canadian transmission pipeline companies. The original 1997 CEPA Stress Corrosion Cracking Recommended Practices (hereafter referred to as the "Practices") were prepared and made public by CEPA in response to a the National Energy Board of Canada's public inquiry MH-2-95 into the problem of stress corrosion cracking (SCC) in oil and gas pipelines. The second edition has been issued to update the original document with the latest scientific knowledge and the changes in field practices of CEPA companies that have evolved since the issue of the first edition. Use of these Practices described herein is wholly voluntary. The Practices described are not to be considered industry standards and no representation as such is made. It is the responsibility of each pipeline company, or other user of these Practices, to implement practices regarding SCC that suit their specific pipelines, needs, operating conditions, and location. Information concerning SCC continues to grow and develop and, as such, these Practices are revised from time to time. For that reason, users are cautioned to confer with CEPA to determine that they have the most recent edition of these SCC Recommended Practices. While reasonable efforts have been made by CEPA to assure the accuracy and reliability of the information contained in these Practices, CEPA makes no warranty, representation or guarantee, express or implied, in conjunction with the publication of these Practices as to the accuracy or reliability of these Practices. CEPA expressly disclaims any liability or responsibility, whether in contract, tort or otherwise and whether based on negligence or otherwise, for loss or damage of any kind, whether direct or consequential, resulting from the use of these Practices. These Practices are set out for informational purposes only. References to trade names or specific commercial products, commodities, services or equipment constitutes neither an endorsement nor censure by CEPA of any specific product, commodity, service or equipment. The CEPA SCC Recommended Practices are intended to be considered as a whole, and users are cautioned to avoid the use of individual chapters without regard for the entire Practices. ©2007 Canadian Energy Pipeline Association Table of Contents v Table of Contents 1. Foreword .........................................................................................................1-1 2. Introduction to the Recommended Practices...............................................2-1 3. Definitions and Abbreviations .......................................................................3-1 4. SCC Management Program............................................................................4-1 5. SCC Investigation Programs..........................................................................5-1 6. In-Line Inspection ...........................................................................................6-1 7. CEPA Recommended Data Collection ..........................................................7-1 8. SCC Condition Assessment ..........................................................................8-1 9. Prevention and Mitigation ..............................................................................9-1 10. Risk Assessment ..........................................................................................10-1 11. Post Incident Management ..........................................................................11-1 12. Circumferential SCC .....................................................................................12-1 ©2007 Canadian Energy Pipeline Association Foreword 1-1 1. Foreword In continuing their lead role in transgranular SCC management, CEPA and its member companies have undertaken a revision of the 1997 SCC Recommended Practices in this current document. This revised document will incorporate the advancements to date in the understanding of transgranular SCC and in the practices with which a pipeline operator can manage transgranular SCC. Although much of this document is similar in content and format when compared to the 1997 SCC Recommended Practices, several major changes were made in this new document. The major technical changes in the 2007 CEPA SCC Recommended Practices include; • The removal of the original definition of “Significant” SCC. • A new SCC management flowchart that aligns more closely with current industry best practices. • The introduction of a multi-level SCC severity assessment method to guide pipeline companies in determining the seriousness of any SCC discovered, as well as the mitigation required. • Clarification of the use of the terms “interlinking” and “interacting”. • Increased guidance in assessing SCC within corrosion. • The formal incorporation of circumferential SCC within the document. • The addition of guidance during post SCC incident investigation and pipeline return to service. • Less emphasis on the use of soils models as the primary SCC assessment and risk reduction tool. 1.1 Scope The “CEPA SCC Recommended Practices” deals exclusively with the transgranular (also known as near-neutral pH or low pH SCC) form of SCC (hereafter simply referred to as “SCC”) and, although some of the management techniques may be similar to those dealing with the intergranular form of SCC (also known as classical SCC or high-pH SCC), this document does not specifically address the intergranular form of SCC. However the document addresses both axial and circumferential Transgranular SCC. ©2007 Canadian Energy Pipeline Association Chapter 2 2. Introduction to the Recommended Practices .........................................2-2 2.1 The Canadian Energy Pipeline Association ............................................................2-2 2.2 CEPA and Stress Corrosion Cracking ....................................................................2-2 2.3 Goals & Objectives..................................................................................................2-3 2.4 SCC Overview.........................................................................................................2-3 2-2 Introduction to the Recommended Practices 2. Introduction to the Recommended Practices 2.1 The Canadian Energy Pipeline Association The Canadian Energy Pipeline Association (CEPA) represents energy transmission pipeline companies that transport over 97% of the crude oil, petroleum products and natural gas produced in Canada. CEPA’s member companies own and operate more than 100,000 kilometres of pipeline across Canada, transporting natural gas and liquid petroleum products to North American markets, providing for the energy needs of millions of consumers. 2.2 CEPA and Stress Corrosion Cracking The discovery of a new form of stress corrosion cracking (SCC) in the early 1980s on a CEPA member pipeline posed a new and little understood integrity issue for this particular pipeline. Prior to the discovery of this new form of cracking, SCC was thought to be a relatively well-understood, intergranular cracking phenomenon occurring on the external surface of pipelines. This original form of Intergranular SCC was first discovered in 1965 in the southern U.S.A. and was constrained to pipeline surfaces subject to a well defined window of elevated temperatures, elevated pH and depressed cathodic potential. The new form of SCC was markedly different in both its growth mechanism and in the environmental conditions in which it was found. This new form of SCC propagated in a transgranular fashion and was found on surfaces in contact with a dilute, near-neutral pH electrolyte, at relatively low pipeline surface temperatures, and under coatings believed to shield the pipe from the cathodic protection system. As such, the newly discovered form of SCC is equally referred to as Transgranular SCC or Near-Neutral pH SCC. Subsequent to the first discovery of Transgranular SCC, several other Canadian pipeline operators have also detected Transgranular SCC on their systems. As well, pipeline operators in Europe, Asia, Australia and the U.S.A have since documented the presence of Transgranular SCC. This phenomena has been identified as the cause of several in-service pipeline failures and continues to be an integrity threat for existing commodity transmission pipelines. Maintaining pipeline integrity is a priority for the industry today and will be in the future. In 1994, CEPA recognized the challenge posed by Transgranular SCC and established an ad-hoc SCC Working Group to share SCC experience and develop pipeline industry protocols to address the issue of SCC. An outcome from the CEPA SCC Working Group was the original 1997 edition of