Post on 19-Jun-2015
S a u d i A r a m c o
Managing SCC in Gas Pipelines
Nader Al-Otaibi Oct 4th, 2011
© Copyright 2011, Saudi Aramco. All rights reserved.
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
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RIYADH
AL MADINAH
YANBU’
QAISUMAH
QASSIM
HAWTAH
KHURAIS
SHEDGUM
‘UTHMANIYAH
HARADH
SHAYBAH
DHAHRAN
ABQAIQ
QATIF
RAS TANURA
JUBAIL
SAFANIYA
HAWIYAH
Mothballed
In Operation
Rabigh
Pipelines Network Description
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1940 1950 1970 1980 1990 2002 2009 2014
1000 1500 2500
5500
12500
18000 19300
22050
Pipelines Network Description
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<20” 22-46” >46”
25% 40% 35% Sizes
35% 36% 29% Service
Crude Gas Product & NGL
44% 33% 23% Age
<20 Years 20-30 Year >30 Year
What is SCC?
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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
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SCC Mechanism
• Active Path dissolution
– Accelerated localized
Corrosion: crack tip
– Material bulk Passive
– Inter-granular
– Active path: Grain boundary
– Stress helps open crack tip
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• Hydrogen Embrittlement
– H2 dissolves in all materials
between atoms
– H2 weaken material
– H2 attack High tensile stresses
areas, notches and stress raisers
– H2 makes cleavage easier
SCC Types
• High PH SCC
– Carbonate/bi-Carbonate
– PH: 9.5-10
– Active path dissolution
– Inter-granular
– Sensitive to temperature (40 ᵒC)
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• Near Neutral (Low) PH SCC
– Many species at reduced
concentrations
– PH: 6.4 (near neutral)
– Hydrogen embrittlement
– Trans-granular
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
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Contributing Factors
• Role of Stress
– Hoop stress 60% of SMYS
– Secondary loading
– Stress concentration
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Contributing Factors
• Role of Temperature
– Distance from compressor
– 40 ᵒC
– Exponentially decrease
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How to Predict and Manage SCC?
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Demonstrated with a Case Study
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
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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
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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
– Un-failed SCC
• Advantage to ILI
– Varying cost
• Very high if summed to pipeline outage cost
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Lower Consequence
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)
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EMAT Technology
• Working Principle:
– SCC detection
– Coating Disbonded
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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
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
Case Study: Gas Pipeline
• Verification Program
– Refine ILI tools findings and complement inadequacy
– Improve ILI Analysis (learning curve)
• MPI
• Shear Wave UT
• Phased Array
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Case Study: Gas Pipeline
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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*
40” Gas Pipeline (three segments) Built: 1971 (south to North) API 5L Gr. X52/60, Tape-Wrap Coated
Case Study: Gas Pipeline
• Verification Program
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Case Study: Gas Pipeline
• Verification Program
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Case Study: Gas Pipeline
• Failure Analysis
– Sample defect
– Lab Failure Analysis
– Longitudinal Cracks
– High PH
– Inter-granular Cracks
– Carbonate/bi-Carbonate
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Case Study: Gas Pipeline
• Action Plan
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Crack classification Type of repair
Open or leaking cracks >60% These cracks shall be replaced. If the replacement pipe 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 Colonies with more than three
linear parallel cracks
These should be repaired by installing a repair sleeve.
Cracks with a depth ranging from 10% to 20%
The cracks should be removed by grinding. The maximum length of cracks shall not exceed 24”.
Cracks with a depth less than 10%
The cracks should be removed by grinding
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
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To Recap
• What is SCC?
• What contributes to it?
• How to predict SCC?
• How to manage it?
• Case Study
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SCC … Don’t Wait for it!
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Thank You
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