Assistu’s client wished to perform FFS and re-rate assessment on pipelines that have been idle for 2 years. The pipelines are scheduled for a service re-start with increased maximum allowable working pressure (MAWP) and design temperature. Six pipelines were chosen for inspection, all with signs of notable metal loss.
From 6 pipelines that have been chosen for inspection, 4 separate defect assessment criterion calculations were completed to accommodate for the different pipe sizes and thicknesses in question, and 20 UT scan reports were reviewed for defect sizes, shapes, and defect trends. The operation history of the individual pipeline was also closely assessed. A final report including the result of the assessment and recommendations, as well as separate technical memos on each pipeline, were created at the end of the project.
Four separate metal loss assessments based on API 579 Part 5 Level 1 were completed for each pipe schedule, and minimum required wall thickness at the re-rate operating conditions were obtained. 20 UT scan reports of the pipes were analyzed using the failure criterion for guidance.
Based on the size of the defect, Assistu has concluded that out of 6 pipelines, 4 have failed the API 579 Part 5 Level 1 assessment and are not safe for operation. Metal loss orientation, weld seam locations, and past operations were closely analyzed to support the conclusion.
By assessing the lines with FFS techniques, the client was able to acquire confidence in their final decision. Though the end result was not desirable and can have costly implications, with Assistu’s evaluation and reporting the final decision is easily understood and justified.