2. Managing SCC in Gas Pipelines
Contents
β’ Saudi Aramco Pipelines
Network
β’ Part I: What is SCC?
β’ Part II: How to Predict and
Manage SCC?
β Assessment Techniques
β Technology: EMAT Program
β Revalidation
β Case Study
β’ Conclusion
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7. SCC: what is it?
β’ SCC: Stress Corrosion
Cracking
β Environment
β Susceptible Material
β Stress
β’ Typical: Older Pipelines!
β’ SCC Characteristics and
Types:
β No significant metal loss
β Perpendicular to T.S.s
β Inter or trans-granular
β High PH vs. Near-Neutral
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8. SCC Mechanism
β’ Active Path dissolution β’ Hydrogen Embrittlement
β Accelerated localized β H2 dissolves in all materials
Corrosion: crack tip between atoms
β Material bulk Passive β H2 weaken material
β Inter-granular β H2 attack High tensile stresses
areas, notches and stress raisers
β Active path: Grain boundary
β H2 makes cleavage easier
β Stress helps open crack tip
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9. SCC Types
β’ High PH SCC β’ Near Neutral (Low) PH SCC
β Carbonate/bi-Carbonate β Many species at reduced
concentrations
β PH: 9.5-10
β PH: 6.4 (near neutral)
β Active path dissolution
β Hydrogen embrittlement
β Inter-granular
β Trans-granular
β Sensitive to temperature (40 α΅C)
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10. Contributing Factors
β’ Environment
β Soil Condition
β’ Wet soil
β’ High salinity and water table
(Subkha)
β Coating Conditions
β’ Tape wrap and Coal-tar
coating
β’ No SCC in FBE coated
pipelines
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11. Contributing Factors
β’ Role of Stress
β Hoop stress 60% of SMYS
β Secondary loading
β Stress concentration
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16. Assessment Techniques
β’ Hydro-test Program
β Fail critical and near-critical SCC
β’ Lower consequence
β Blunt non-mature SCC
β’ Might plastically deform
crack tip which might
accelerate failure!
β Requires Criteria
Lower Consequence
β Un-failed SCC
β’ Advantage to ILI
β Varying cost
β’ Very high if summed to
pipeline outage cost
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17. EMAT Technology
β’ Need Drives Technologies β¦
β Aramco runs a Master Sales Gas Network that supports
growing gas local demand
β Reliable supply ο no interruption
β Aramco search of technology to revalidate pipelines
integrity with respect to SCC
β’ Difficulties of hydro test
β’ ILI: EMAT (Electro-Magnet Acoustic
Transducers)
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19. SCC Revalidation Criteria
β’ ILI Optimization Criteria
β’ Category A pipelines
β Pipelines History of Stress Corrosion Cracking
β’ Category B pipelines
β Similar Pipelines Environment (soil condition)
β’ Category C pipelines
β ASME B31.8S β MANAGING SYSTEM INTEGRITY OF
GAS PIPELINES
β ANSI/NACE Standard RP0204 β Stress Corrosion
Cracking (SCC) Direct Assessment Methodology
20. ASME B31.8S HCA Definition
β’ Identifying SCC Susceptible Areas (ASME
B31.8S)
β Operating stress > 60% SMYS
β Operating temperature > 100Β°F (for high pH SCC)
β Distance from compressor β€ 20 miles (β€ 32 km)
β Pipeline age β₯ 10 years old
β Coating is other than FBE
21. Case Study: Gas Pipeline
β’ Verification Program
β Refine ILI tools findings and complement inadequacy
β Improve ILI Analysis (learning curve)
β’ MPI
β’ Shear Wave UT
β’ Phased Array
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22. Case Study: Gas Pipeline
40β 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*
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25. Case Study: Gas Pipeline
β’ Failure Analysis
β Sample defect
β Lab Failure Analysis
β Longitudinal Cracks
β High PH
β Inter-granular Cracks
β Carbonate/bi-Carbonate
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26. Case Study: Gas Pipeline
β’ 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 24β.
Cracks with a depth less than
The cracks should be removed by grinding
10%
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27. Tackling the Contributing Factors !
β’ New Coating Technologies
β Success of existing technologies
β’ Visco-Elastic; good track record within Saudi Aramco
β Realized Potential of some coating technologies
β’ Under Approval
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28. To Recap
β’ What is SCC?
β’ What contributes to it?
β’ How to predict SCC?
β’ How to manage it?
β’ Case Study
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