FITNESS-FOR-SERVICE ASSESSMENT OF GIRTH WELDS OF PIPELINE BASED ON ANALYTIC HIERARCHY PROCESS AND FAILURE ASSESSMENT DIAGRAM

Weld defect is one of the main reasons leading to the failure of pipelines. Therefore, the fitness-for-service assessment of girth welds along the whole pipeline should be carried out before pipeline boosting or resuming production, so as to eliminate the hidden danger and determine the appropriate pressure range of it. Due to the fact that most pipeline laying locations are underground, it is difficult to accurately obtain the load parameters at the welds. The existing fitness-for-service assessment of girth welds is mainly based on the internal pressure of pipelines and ignores the influence of additional load, which results in inaccurate evaluation results. In this paper, the fitness-for-service assessment of girth welds along a long-distance natural gas pipeline was carried out using the results of non - destructive testing after the excavation of girth weld as the basic data, using the failure assessment diagram in standardized API579 as the evaluation method, and determining the additional load at the welds through AHP, providing decision support for pipeline safety. The method and criterion can be used for reference in the engineering practice of girth weld fitness-for-service assessment for the whole pipeline of long distance pipeline in service.