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Stress Corrosion CrackingOverview & Introduction
David Johnson
December 2, 2003
SCC History
• Not a recent phenomenon
• Not exclusive to pipelines
• Not confined to underground environment
• Not geographically limited
• Ammonia cracking of cartridge brass
• Chloride cracking of stainless steel
Requirements for SCC
Environment
StressMetallurgy
SCC Characteristics
Factor High pH Neutral pH Location CS discharges
Wet-dry soils Aggressive soil
Anywhere Wet-dry soils Aggressive soil
Temperature Exponential temperature impact
Little apparent effect
SCC Characteristics
Factor High pH Neutral pH
Electrolyte Carbonate-bicarbonate pH > 9.3
Dilute bicarbonate 5.5 < pH <7.5 Higher CO2
Potential -600 to –750 mV Free potential
Cracks Intergranular Narrow Not corroded
Transgranular Wider May be corroded
SCC near Seam Weld
Metallography of SCC
ASME Causes of Gas Transmission Incidents
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Vandalism
Stress Corrosion Cracking
Malfunction
Prev. Damgd Pipe
Mfr
Constr/Instal
Other Failures
Unknown
Incorrect Operation
Misc
Natural Forces
Internal Corrosion
External Corrosion
Third Party Damage
Non-Pipe
Pipe
Summary of Incident Causes
Summary of Significance
• Natural gas transmission(1985-2002)– 15 of 1415 total reported incidents
• Liquid transmission (PPTS)– 5 of 472 in database
• NEB (Canada) (1992-2002)– 3 of 23– None since 1995
• Overall - about 1% of incidents
Why Today’s Interest?
• Other, higher significance threats also being addressed
Other Threats (B31.8S)• External Corrosion• Internal Corrosion• Manufacturing Defects• Welding & Fabrication Defects• Equipment Failure• Third Party / Mechanical Damage• Incorrect Operations• Weather & Outside Force
External & Internal Corrosion
• CP systems
• Gas quality standards and monitoring
• Relatively mature ILI capability
• Correlated to hydro-test capability
• Rapidly maturing DA capabilities
Manufacturing & Construction
• Specifications - materials & construction
• Advances in materials technology
• Mill inspections
• Construction inspections
• Proof testing
Third Party Damage
• Dig Safety
• Common Ground Alliance
• One Call enforcement
• Enhanced public awareness
Incorrect Operation
• Operator Qualification programs
• Qualification of controllers
• OQ-2
• B31Q
Equipment Failure
• Gaskets, Seals, Valves, Pumps, etc.
• Generally not pipe
• Generally confined
• Specifications, testing, maintenance
Weather & Outside Forces
• Design & Construction
• Forecasting
• Monitoring
• Better understanding of material responses
Why Today’s Interest?
• Other, higher significance threats also being addressed
• Less apparent understanding
• Small, but widespread, occurrence
• Methods of addressing not as mature– Inspection, characterization, assessment,
management
Today’s Workshop
• Share available information
• Understand application of current management techniques
• Update on R&D
• Future Needs– Technology development– Regulatory approach
Managing SCC
• Operators have found & managed SCC• Tools as prescribed in PLSIA of 2002
– In-Line Inspection– Hydrostatic Testing– Direct Assessment – Other
• All have specific capabilities & limitations• Gas - Liquid Pipeline Differences
Major Challenges
• Finding SCC– Shallow cracks initially– May not be visible to unaided eye
• Gas - Liquid technology differences• Service disruptions• Water disposal• Assessing what is found• Mitigation and Management
Research & Development
• Multi-faceted approach
• Environmental factors
• Surface preparation & coatings
• CP system operation
• Operational factors
• Material behavior
• Detection & sizing
Regulatory Response
• Determining reasonable response
• Setting investigation protocols
• Communication needs
Upcoming Panels
• Operator Experience with Finding and Managing SCC
1. TransCanada
2. Enbridge
3. Kinder Morgan
4. Duke
5. Williams
6. Colonial
Upcoming Panels
• R & D– What’s been done– Current work– Future needs– PRCI– ILIA– NACE
Upcoming Panels
• Regulators– Concerns & Needs– NEB– EUB– MNOPS– USDOT-OPS
