United States Department of Transportation
i
Development of a Commercial Model to Predict Stress Corrosion Cracking Growth Rates in Operating Pipelines
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2011-06-01
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[PDF-2.79 MB]
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Edition:Final Report
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Abstract:Stress corrosion cracking (SCC) in pipelines occurs under two broad pH conditions— alkaline pH and near-neutral pH. SCC can lead to leaks, sudden bursts, or explosions of gas and liquid pipelines. Crack growth rate (CGR) is a critical parameter to be considered when the inspection interval for in-line inspection (ILI) or pressure test, or the reassessment interval for SCC direct assessment (DA) is determined. CGR can also be a key parameter in identifying locations along a pipeline that must be given priority for SCC assessment. The current industrial practice of estimating CGRs is based on empirical approaches, such as assuming a conservative constant rate or a rate obtained through linear extrapolation from measured crack depth(s) over a period of time. Such CGR estimation without including the underlying cracking mechanisms can be fraught with uncertainties. This is because the often non-linear nature of the physical growth of a crack is not reflected in such a method. A CGR model with the crack growth mechanisms embedded is needed for more reliable CGR prediction. The main objective of this project was to develop commercial models for predicting CGRs in operating pipelines useful for prioritization of SCC susceptible locations and for establishing inspection or re-assessment intervals. For high pH SCC, the CGR models were developed based on fundamental principles and then reduced to a commercial tool suitable for practical application. Because the mechanisms of near-neutral pH SCC were not well established, the model developed in this work for this type of SCC still relied on empirical correlations of experimental data reported in the literature. Procedures for field application of the models were provided.
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