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)