Nader Al Otaibi - Managing SCC in Gas Pipelines
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This document discusses stress corrosion cracking (SCC) in gas pipelines and strategies for managing it. SCC occurs due to the combined effect of a corrosive environment, a susceptible material, and applied stress. It can develop in older pipelines without causing significant metal loss. The document outlines Saudi Aramco's large pipeline network and techniques for predicting and assessing SCC, including in-line inspections and the EMAT technology. It also presents a case study of revalidating a 40" gas pipeline segment through verification digging and failure analysis. Strategies discussed for tackling SCC include optimizing assessment criteria, employing new coating technologies, and taking actions based on crack classification.
Nader Al Otaibi - Managing SCC in Gas Pipelines
- 1. Saudi Aramco Managing SCC in Gas Pipelines Nader Al-Otaibi Oct 4th, 2011 © Copyright 2011, Saudi Aramco. All rights reserved.
- 2. Managing SCC in Gas Pipelines Contents • Saudi Aramco Pipelines Network • Part I: What is SCC? • Part II: How to Predict and Manage SCC? – Assessment Techniques – Technology: EMAT Program – Revalidation – Case Study • Conclusion 2
- 3. QAISUMAH SAFANIYA JUBAIL RAS TANURA QASSIM QATIF DHAHRAN AL MADINAH ABQAIQ KHURAIS SHEDGUM RIYADH YANBU’ ‘UTHMANIYAH HAWIYAH Rabigh HARADH HAWTAH SHAYBAH In Operation Mothballed 3
- 4. Pipelines Network Description 22050 19300 18000 12500 5500 2500 1000 1500 1940 1950 1970 1980 1990 2002 2009 2014 4
- 5. Pipelines Network Description <20” 22-46” >46” Sizes 25% 40% 35% Crude Gas Product & NGL Service 35% 36% 29% <20 Years 20-30 Year >30 Year Age 44% 33% 23% 5
- 6. What is SCC? 6
- 7. SCC: what is it? • SCC: Stress Corrosion Cracking – Environment – Susceptible Material – Stress • Typical: Older Pipelines! • SCC Characteristics and Types: – No significant metal loss – Perpendicular to T.S.s – Inter or trans-granular – High PH vs. Near-Neutral 7
- 8. SCC Mechanism • Active Path dissolution • Hydrogen Embrittlement – Accelerated localized – H2 dissolves in all materials Corrosion: crack tip between atoms – Material bulk Passive – H2 weaken material – Inter-granular – H2 attack High tensile stresses areas, notches and stress raisers – Active path: Grain boundary – H2 makes cleavage easier – Stress helps open crack tip 8
- 9. SCC Types • High PH SCC • Near Neutral (Low) PH SCC – Carbonate/bi-Carbonate – Many species at reduced concentrations – PH: 9.5-10 – PH: 6.4 (near neutral) – Active path dissolution – Hydrogen embrittlement – Inter-granular – Trans-granular – Sensitive to temperature (40 ᵒC) 9
- 10. Contributing Factors • Environment – Soil Condition • Wet soil • High salinity and water table (Subkha) – Coating Conditions • Tape wrap and Coal-tar coating • No SCC in FBE coated pipelines 10
- 11. Contributing Factors • Role of Stress – Hoop stress 60% of SMYS – Secondary loading – Stress concentration 11
- 12. Contributing Factors • Role of Temperature – Distance from compressor – 40 ᵒC – Exponentially decrease 12
- 13. How to Predict and Manage SCC? Demonstrated with a Case Study 13
- 14. SCC Management Program • SCC Management Program – Pipe Segment Susceptibility to SCC • Identify segments • Investigate for SCC – Classification of Severity • Plan and implement mitigation • Re-assessment interval – Manage SCC Failure • Plan and implement mitigation • Safe operating pressure 14
- 15. Assessment Techniques • SCC Models – Pipe Excavation Program • Coating removal • Visual inspection • NDT – Historical trends – Effort vs. Accuracy • In-Line Inspection – Specialized tool – Sufficiently reliable – Recommended if coupled with verification digs 15
- 16. Assessment Techniques • Hydro-test Program – Fail critical and near-critical SCC • Lower consequence – Blunt non-mature SCC • Might plastically deform crack tip which might accelerate failure! – Requires Criteria Lower Consequence – Un-failed SCC • Advantage to ILI – Varying cost • Very high if summed to pipeline outage cost 16
- 17. EMAT Technology • Need Drives Technologies … – Aramco runs a Master Sales Gas Network that supports growing gas local demand – Reliable supply no interruption – Aramco search of technology to revalidate pipelines integrity with respect to SCC • Difficulties of hydro test • ILI: EMAT (Electro-Magnet Acoustic Transducers) 17
- 18. EMAT Technology • Working Principle: – SCC detection – Coating Disbonded 18
- 19. SCC Revalidation Criteria • ILI Optimization Criteria • Category A pipelines – Pipelines History of Stress Corrosion Cracking • Category B pipelines – Similar Pipelines Environment (soil condition) • Category C pipelines – ASME B31.8S — MANAGING SYSTEM INTEGRITY OF GAS PIPELINES – ANSI/NACE Standard RP0204 — Stress Corrosion Cracking (SCC) Direct Assessment Methodology
- 20. ASME B31.8S HCA Definition • Identifying SCC Susceptible Areas (ASME B31.8S) – Operating stress > 60% SMYS – Operating temperature > 100°F (for high pH SCC) – Distance from compressor ≤ 20 miles (≤ 32 km) – Pipeline age ≥ 10 years old – Coating is other than FBE
- 21. Case Study: Gas Pipeline • Verification Program – Refine ILI tools findings and complement inadequacy – Improve ILI Analysis (learning curve) • MPI • Shear Wave UT • Phased Array 21
- 22. Case Study: Gas Pipeline 40” Gas Pipeline (three segments) Built: 1971 (south to North) API 5L Gr. X52/60, Tape-Wrap Coated Section III, inspected : August 28, 2010 Summary: 4 (verified) SCC locations* Section II, inspected: July 14, 2010 Summary: 3 (verified) SCC locations* Section I, inspected March 14, 2010 Summary: 8 (verified) SCC locations* 22
- 23. Case Study: Gas Pipeline • Verification Program 23
- 24. Case Study: Gas Pipeline • Verification Program 24
- 25. Case Study: Gas Pipeline • Failure Analysis – Sample defect – Lab Failure Analysis – Longitudinal Cracks – High PH – Inter-granular Cracks – Carbonate/bi-Carbonate 25
- 26. Case Study: Gas Pipeline • Action Plan Crack classification Type of repair These cracks shall be replaced. If the replacement pipe Open or leaking cracks >60% cannot be found, then the sleeve installation option can be worked out, provided that the crack arrestor is used. Cracks with a depth ranging from 20% to 60% Or These should be repaired by installing a repair sleeve. Colonies with more than three linear parallel cracks Cracks with a depth ranging The cracks should be removed by grinding. The maximum from 10% to 20% length of cracks shall not exceed 24”. Cracks with a depth less than The cracks should be removed by grinding 10% 26
- 27. Tackling the Contributing Factors ! • New Coating Technologies – Success of existing technologies • Visco-Elastic; good track record within Saudi Aramco – Realized Potential of some coating technologies • Under Approval 27
- 28. To Recap • What is SCC? • What contributes to it? • How to predict SCC? • How to manage it? • Case Study 28
- 29. SCC … Don’t Wait for it! 29
- 30. Thank You 30