Crack growth rate (CGR) is a critical parameter in pipeline integrity management for estimating the time needed for the next in-line inspection (ILI) or pressure test or the reassessment interval for direct assessment. The current industrial practice of estimating CGRs uses a constant rate or a rate obtained through linear extrapolation. Without including the underlying cracking mechanisms to account for the physical non-linear growth of a crack, such an estimate can be fraught with uncertainties. Mechanistic CGR models for pipeline high pH stress corrosion cracking (SCC) are often sophisticated, contain many model parameters, of which some may not be known or cannot be measured in the field. Thus, direct field use of these models is challenging. This paper reports a method developed for making field use of the mechanistic models by grouping the variables. Such a model with fewer model parameters still retains the mechanistic nature of the original models and, if calibrated with field data, will allow for predicting a future CGR. A four-step procedure was proposed for field use of the models as an alternative to existing methods. A proper CGR should be determined by evaluating all CGRs obtained from different methods and by using expert’s best judgment.
Stress corrosion cracking (SCC) in pipelines occurs under two broad pH conditions – alkaline pH and near-neutral pH.1 SCC can lead to leaks, sudden bursts, or explosions of gas and liquid pipelines.1-2 Crack growth rate (CGR) is a critical parameter to be considered when an inspection interval for in-line inspection (ILI) or pressure test, or a reassessment interval for SCC direct assessment is determined. This is because the often physical non-linear growth of the crack is not reflected in such a method. A CGR model with the crack growth mechanisms embedded is needed for a more reliable CGR prediction.
