SCC Direct Assessment
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Transcript of SCC Direct Assessment
SCCDirect Assessment
John A. Beavers
Chairman of NACE TG 273 on SCC DA
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SCC DA Program
Stress-corrosion-cracking direct assessment (SCCDA) is a structured process that contributes to pipeline company’s efforts to improve safety by reducing the impact of external SCC on pipeline integrity.
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Scope of NACE SCC DA Recommended Practice
Addresses buried onshore petroleum (natural gas, crude oil, and refined products) pipelines constructed from line-pipe steel.
Addresses the situation where a pipeline company has identified a portion of its pipeline as an area of interest with respect to SCC based upon its risk assessment process and has decided that SCCDA is an appropriate approach for integrity assessment.
Provides flexibility for an operator to tailor the SCCDA process to a specific pipeline situation.
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SCC DA Program
SCC DA: One component of SCC integrity management program
Other Components
In-Line Inspection
Hydrostatic Testing
Repair and Replacement
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SCC DA Program
All of the available techniques for SCC integrity management have strengths and weaknesses.
A combined approach is generally most effective.
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Determine whether pipeline system is susceptible.
To SCC
To significant SCC
Prioritize system for ILI, hydrostatic testing, or other forms of remediation where significant and extensive SCC is found.
Purposes of SCC DA Program
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Members from pipeline operating companies
Natural Gas and liquids
Members from engineering services companies
Researchers
Representatives from PRCI
NACE SCC DA TASK GROUP
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Step 1 (Pre-Assessment) Evaluation of existing data
Step 2 (Indirect Inspections) Collection of additional required data
Prioritization of pipeline segments
Site selection
Componentsof SCC DA Program
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Componentsof SCC DA Program
Step 3 (Direct Examinations)
Field verification of selected sites
Excavation and examination
Step 4 (Post Assessment)
Evaluation and documentation
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Step 1 (Selection of Susceptible Segments)
High-pH SCC: Follows ASME B318S Appendix A3 for selection of susceptible segments
Age of Pipe (>10 Years)Operating Stress Level (>60% of SMYS)Operating Temperature (>100 F)Distance from Compressor Station (<20 miles)Coating Type (All but FBE)
Prior history of SCC (service or hydrostatic test failure)
Unless conditions were corrected
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Step 1 (Selection of Susceptible Segments)
Near Neutral pH SCC: Uses same criteria excluding temperature
Age of Pipe (>10 Years)Operating Stress Level (>60% of SMYS)Distance from Compressor Station (<20 miles)Coating Type (All but FBE)
Prior history of SCC (service or hydrostatic test failure)
Unless conditions were corrected
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Prioritize segments and select sites based on probability and consequences
Probability Coating type, age, stress level, historical information, in-
line inspections, terrain models, other operators experience base
Consequences Proximity to public, product type, pipe diameter and
operating pressure
Steps 1 and 2
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Field verification of sites selected Based on factors used for site selection
Conduct field digs Examine pipe for SCC
Evaluate SCC if foundType and severity of cracking
Collect other relevant dataExtent depends on use
Step 3
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Objectives Determine whether general SCC mitigation
is required. Define reassessment intervals. Evaluate the effectiveness of the SCCDA
approach.
Post Assessment (Step 4)
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Post Assessment (Step 4)
Primary guidance for SCC mitigation is provided in Part A3 of ASME B31.8S.
Each company is responsible for selecting post assessment options.
SCC Mitigation Definition of reassessment intervals Evaluation of effectiveness of SCC DA
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Post Assessment (Step 4)
No SCC Found Recoat Pipe at disbondments or where
coating has been removed Evaluate re-inspection interval
SCC Found Repair or replace pipe joint Engineering critical assessment (ECA) to
evaluate risk and identify mitigation methods
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Post Assessment (Step 4)
Non Significant SCC Found Engineering critical assessment (ECA) to
determine whether cracks should be removed. Recoat Pipe at disbondments or where
coating has been removed. Evaluate re-inspection interval.
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Post Assessment (Step 4)
Isolated Significant SCC Requires Discrete Mitigation Options for Discrete Mitigation
Repair or removal of the affected pipe lengthHydrostatically test the pipeline segment In-Line inspection where appropriate tools are
availableEngineering critical assessment to evaluate the
risk and identify further mitigation methods
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Post Assessment (Step 4)
Widespread Significant SCC Requires General Mitigation Options for General Mitigation
Hydrostatic testing of affected segments In-Line inspection where appropriate tools are
available Pipe replacement in affected segments Re-coating of affected segments
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Summary
SCC DA is one component of an SCC integrity management program.
Other components include in-line Inspection, hydrostatic testing, and repair and replacement.
A combined approach is generally most effective.
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Summary
Four Components of SCC DA Program Step 1 (Pre-Assessment) Step 2 (Indirect Inspections) Step 3 (Direct Examinations) Step 4 (Post Assessment)