EVALUATING PIPELINE OVALITY ACCEPTABILITY CRITERIA FOR STRAIGHT PIPE SECTIONS

摘要

Pipe ovalization, a deviation from the circular nominal cross section, is a common occurrence during the manufacturing of pipe sections. Additionally, ovalization can also occur in pipelines during and after installation and construction. CSA Z662-11 [1] provides an acceptance criteria of 5% for pipeline ovality in bends, however there is a variation in acceptance criteria for pipe ovality occurring in straight pipe sections. An industry review of pipeline design, operation, and maintenance codes was conducted to determine the industry acceptance for ovality limits in straight pipe sections. Based upon this industry review, the ovality limits were evaluated against constructability limits, limitations for passage of inline-inspection (ILI) tools, as well as evaluating the stress in an ovalized pipe section compared to the maximum allowable stress of the pipe. During this review, it was revealed that allowable stress was the limiting factor for pipeline ovality, compared to constructability and ILI tool passage, thus this paper primarily discusses limitations related to remaining strength for ovalized pipe sections. The API 579 Fitness-for-Service assessment was used to evaluate varying levels of ovality to determine acceptability criteria for ovalization in straight pipe. The criteria was first established using a level 2 Fitness-for-Service assessment, which was then evaluated with a level 3 assessment using finite element analysis. This criterion was evaluated using multiple pipeline diameters and wall thickness in order to determine scalability.