Transitioning from hydrostatic testing to in-line inspection for pipelines with challenging seam welds

摘要

For some pipelines with challenging low frequency electric resistance welded (LF-ERW) seams and arduous operational profiles, hydrostatic testing has remained the preferred integrity assessment approach. But with the elimination of in-service ruptures, the operators of these pipelines seek an alternative seam assessment method that provides a sufficiently conservative integrity assessment without the potentially negative impacts of hydrostatic testing. As in-line inspection (ILI) and field non-destructive evaluation (NDE) improve, anomalies can be better assessed. With improved ILI assessments, pipelines that have been historically hydrostatically tested can now use ILI to ensure operational integrity. The improved ILI technology assessed in this work is an enhanced ultrasonic crack ILI tool with higher circumferential resolution and finer axial sample intervals. The key is combining the knowledge of the population of potential anomalies with improved assessment approaches. Historic ILI data can often help with identification of noncritical anomalies types. In addition, the emerging full matrix capture (FMC) imaging method that quantifies the size, position, and orientation of seam weld anomalies was examined to better understand the ILI capabilities and limitations. This paper discusses the work performed to ensure the efficacy of the improved ILI and NDE methods to accurately detect and quantify all anomalies that could possibly fail a hydrostatic test. An early step in the process was removing three sections of pipe from service for technology adjustment and assessment. Each spool was examined with ILI technology in a pump-through facility, inspected using many NDE methods and then destructively tested. These results were communicated to ILI analysts and used to refine and improve the interpretation of the inspection results. Then the pipeline was inspected as part of the scheduled integrity assessment. Using field evaluation of anomalies detected by ILI, pipes were selected for removal from service for pressure testing and destructive examination. This paper presents the inspection and destructive testing results in addition to the prognosis for the use of the ILI in lieu of hydrostatic testing for LF-ERW pipe. Inline Inspection, Seam Weld, Prioritization, Integrity Assessment, ERW, ILI