Development of a SCC Crack Growth Rate Calculator

Abstract Estimation of representative Crack Growth Rates (CGR) for pipelines with confirmed Stress Corrosion Cracking (SCC) is an Integrity management challenge. Published rates used within the industry can be unreliable, as most estimates assume a particular range of time periods for when cracks initiated, without providing reliable evidence for when crack initiation occurred. Also, little detail is provided to help assess whether the published rate could be applied to similar asset of interest. Laboratory testing (often used to determine industry published CGRs) tends to be under Stage II growth conditions where the CGRs are known to be much higher than compared to Stage III conditions. As a result, reported maximum CGRs can vary greatly from approximately 5 mm/yr (from laboratory testing) to approximately 0.8 mm/yr (from infield estimates, where operational conditions are not generally provided). These values are known to be very conservative, so a “rule of thumb” rate of 0.3 mm/yr is commonly used throughout the pipeline industry as an SCC growth rate. This estimate of 0.3 mm/yr is still considered to be conservatively aggressive when compared with reliably obtained rates of 0.15 mm/yr or lower. To support operators, an SCC Crack Growth Rate Calculator has been developed to bring together the different parameters known to affect SCC crack growth rates in order to provide an initial, conservative crack growth rate for individual anomalies (reported or hypothetical) located along a specific pipeline.