Validation of Dent Fatigue Life Screening and Assessment Methods in API RP 1183

Abstract Mechanical damage (MD) assessment and management tools have been developed on behalf of Pipeline Research Council International (PRCI), Interstate Natural Gas Association of America (INGAA), Canadian Energy Pipeline Association (CEPA), other research organizations and individual pipeline operators. Many of these tools are included in API Recommended Practice (RP) 1183. The current paper discusses the results of a study undertaken to validate the various dent fatigue life screening and assessment methods that were developed as part of various CEPA and PRCI projects, some of which have been incorporated into the first edition of API RP 1183. The work presented in this paper involved performing detailed analysis of data provided by pipeline operators for digs where mechanical damage features were identified by in-line inspection (ILI) systems and subsequently excavated and inspected in the ditch using non-destructive examination (NDE) methods. In total, data for 1320 dents were provided for review by pipeline operators based on their dent integrity management programs. More than 10% of these dents were found to have cracks during the in-ditch non-destructive inspection. Detailed dent geometry data, pressure data and in-ditch inspection reports were reviewed and analyzed to perform dent severity analysis. Factors such as pipe geometry, dent shape, dent restraint condition, effect of co-incident features and operational pressure cycle severity were considered to understand the strength of the relationship between various factors and the estimated dent fatigue life. The data was used to evaluate and validate the performance of the dent fatigue life screening and assessment methods developed as part of various CEPA and PRCI projects, some of which have been incorporated into the first edition of API RP 1183.