Managing Rooftopping: An In-Line Inspection Based Approach

Variation in longitudinal seam weld geometries can pose a challenge for liquid operator’s crack management programs. Both, radial misalignment and angular misalignment (also known as “peaking” or “rooftopping”) contribute to what is termed an “anomalous” seam weld geometry. These anomalous geometries create two challenges for an operator’s crack management program: they can reduce the fatigue life of the seam weld due to an increased stress concentration; and they create an unexpected geometry which challenges crack in-line inspection tools. The combination of these challenges can create a situation where a seam weld flaw can propagate at a higher rate without being detected by in-line inspection technologies, increasing the risk of failure. It is therefore prudent for operators to understand where they may have anomalous seam weld geometries and adjust their crack management plan accordingly. This paper outlines the approach taken by TC Energy to leverage existing datasets to quantify anomalous seam weld geometries, and more specifically rooftopping, on pipe following an incident. Several different in-line inspection technologies were investigated to quantify the presence of rooftopping, with various levels of success. One of the most promising approaches involved sensor stand-off data of an ultrasonic wall thickness measurement technology. The technology was initially pulled through a calibration spool in which rooftopping was artificially introduced. Through collaboration between the TC Energy and NDT Global, an algorithm was developed to not only detect, but also size the levels of rooftopping within the pipeline. The results of the excavation program found that the technology could adequately detect rooftopping. The absolute sizing of rooftopping is an area of focus for future improvements; however, the ability to detect rooftopping allows for a better understanding of the pipeline system and adds another level of data integration which TC Energy has used to improve their liquids crack management program.