Crack and fitness-for-service assessment of ERW crude oil pipeline

Twelve crack accidents took place on a 273.1 × 6 mm X52 ERW newly built crude oil pipeline during air pressure tests. This paper gives a detailed investigation on the crack accidents. Macro-fractography and micro-fractography of cracked line pipes were conducted, and the quality of the weld and pipe body were inspected. It was found that the main cause of line pipe failures at the weld was lack of fusion defects and cracks produced by inadequate welding heat input in electric resistance welds (ERWs). Considering that there were still lack of fusion defects and cracks on the pipeline after internal pressure tests, a fitness-for service (FFS) assessment was performed for the pipeline by use of failure assessment diagram technology and Monte-Carlo technology of failure probability. It was showed from FFS that the pipeline could break under designed operating pressure, and the maximum operation pressure was predicted for the pipeline.