In-Service Dent Management From an Operator’s Perspective Available to Purchase

Pipeline dents are common occurrences that have a potential integrity threat to the system. Dents are typically found through in-line inspections, and historically, low-resolution in-line inspection geometry tools were used to find the locations of dents. These tools gave little information about shape, orientation or other dent features. Newer ‘high-resolution’ tools give a much clearer picture of the dent shape, location, orientation and location of welds. This information has been previously unavailable and has enabled dent integrity assessment with much greater accuracy and confidence. However this still leaves the question of how to best address the information from older, low-resolution inspection tools. In the past, CSA Z662 required that all dents with a deflection greater than 6% or that contained stress concentrators, including welds, had to be repaired. In the newly published 2003 edition of CSA Z662, dents can be assessed by an engineering assessment to determine their acceptability. Historical evidence has shown that dents less than 6% can also be subject to failure under certain conditions, and is indicated in the notes of CSA Z662-03 10.8.2.4.2. Dents that contain stress concentrators, including corrosion, welds and cracks must be given special consideration, however often little information is available for the dent from solely a geometry tool. TransCanada PipeLines Limited has been involved in the development of a dent assessment methodology for several years. Based on the 2003 revisions to CSA Z662, TransCanada has started to implement a dent integrity management program. This paper discusses the approach taken by TransCanada: to create a database of dent features, classification of dents, finite element analysis (FEA) to determine cyclic stress spectra, fatigue analysis, validation through dig programs, and the management of these features from a system integrity standpoint.