Pipeline dents can be developed from the pipe resting on rock, a third-party machinery strike, rock strikes during backfilling, amongst other causes. The long-term integrity of a dented pipeline segment is a complex function of a variety of parameters including pipe geometry, indenter shape, dent depth, indenter support, secondary features, and pipeline operating pressure history at and following indentation. In order to estimate the safe remaining operating life of a dented pipeline, all of these factors must be considered and guidelines for this assessment are not available.
US DOT regulations (49 CFR 192 and 195) include dent repair and remediation criteria broadly based upon dent depth, dent location (top or bottom side), pressure cycling (liquid or gas), and dent interaction with secondary features (weld, corrosion, cracks). The criteria defined above are simple to use, however, they may not direct maintenance to higher risk dent features and be overly conservative or, in some cases, unconservative.
PRCI, USDOT, CEPA and other full-scale testing, finite element modelling and engineering model development research has been completed to evaluate the integrity of pipeline dents. These results have demonstrated trends and limits in dent behavior and life that can improve on existing codified and traditional treatment of dents. With these research results a guideline for dent management can be developed to support operators develop and implement their pipeline integrity management programs.
This paper provides an overview of the newly developed API recommended practice for assessment and management of dents (RP 1183). The RP considers dent formation strain, failure pressure and fatigue limit states including the effects of coincident features (i.e. welds, corrosion, cracks and gouges). This paper will focus on how pipeline operators can derive value from this step change in integrity management for dents. The paper describes the basis for the dent screening and integrity assessment tools included in the RP. This RP provides well founded techniques for engineering assessment that may be used to determine the significance of dent features, if remedial actions are required and when these actions should be taken.