Lessons learned during the in-line inspection of a pipeline containing bell-and-spigot joints, chill rings, and mitre bends

摘要

PG & E,a US-based natural-gas transmission pipeline owner and operator, recently completed the in-line inspection of one of its pipelines, located in Contra Costa and Alameda Counties, California. The pipeline is approximately 41.1 km of 24in OD, with wall thickness of 7.14-14.27mm (0.281-0.562in),API5L Grades B, X42, X52, and X60. The pipeline was originally constructed in 1944 from random mill lengths and was field welded using shielded-metal-arc welding; it has an MAOP of 34.5 bar (500psi) [1]. This pipeline contains many features such as mitre bends, chill rings, and bell-and-spigot joints installed during its original construction, as well as 1.5-D radius forged elbows installed in recent decades. These fixtures, along with the fact that the pipeline operated at low pressures and volumes, caused the in-line inspection of this line to be challenging.This case study discusses the methods used and lessons learned throughout a three-year effort to upgrade, traverse, and inspect this pipeline with an in-line inspection tool.