As part of a program to increase the operating pressure of a 20” (508.0mm) natural gas pipeline, a careful plan was developed and executed to ensure the integrity of the pipeline. The pipeline was built in 1943 using linepipe produced having a DC ERW longitudinal seam weld and travels along a densely populated route in the suburbs of Philadelphia. The work plan included ILI inspection methods to detect corrosion (MFL tool), mechanical damage (geometry tool), and ERW seam weld defects (TFI MFL tool). After the anomalies were identified and the necessary pipe replacements were completed, the pipeline was hydrostatically tested prior to being returned to service at the newly established operating pressure. The paper will describe the project planning process used to ensure the fitness and reliability of the pipeline and provide a review of the ILI results, excavations, pipe replacements, and hydrostatic test experiences. Of particular interest were the capabilities and limitations of the TFI tool to detect, discriminate, and size ERW seam weld defects. Seam weld defects were evaluated using ILI inspection methods and in many cases field prove-up ultrasonic inspection methods. When an ERW defect was confirmed by field NDT prove-up, the pipe section was removed and metallographic work was conducted to characterize the ERW flaw size and nature. A correlation was then possible between the sizing capability of the TFI tool, the ultrasonic prove-up method, and the actual defect size. All this information is useful to establish a level of confidence in defect sizing for future project needs. The final validation of the pipeline fitness at the higher operating pressure was established through the successful hydrostatic test. A short summary will be given on how the pipeline fitness was qualified and demonstrated.
Radiographic and Ultrasonic Inspection of Duplex and Austenitic Stainless Steels Weld Defects that Formed After TIG Welding
