Discussion and thinking of high-grade pipeline girth weld strength matching

Abstract

Nowadays, failure of girth weld is a main risk factor for the operation of high-grade long-distance pipelines.Through the analysis on girth welds of failed pipelines, it is found that the strength of girth welds lower than that of the pipe body is one of the important reasons why the pipeline is easy to fracture under the action of ground movement. Thus,research on strength matching of pipeline girth welds has become the basic subject to analyze the girth weld cracking of inservice pipeline and prevent the hazard of new pipeline girth welds. Herein, the definition, development process and basic features of strength matching were summarized, the impact of strength matching on plastic and fracture failure of pipeline girth weld was analyzed, and the development of failure assessment technology taking the strength matching conditions into account was sorted out. Meanwhile, three concepts on status partition of stress-strain under different strength matching conditions were proposed based on the development history and status of high-grade steel and matching conditions of its welding structure. Besides, it was recommended to use the axial yield strength difference as the definition of strength matching of high-grade pipelines, form a definite quantitative characterization method and regard it as the key parameter for design and engineering quality control. Therefore, it is expected to promote the unified understanding on strength matching of high-grade pipeline girth weld, improve the standardization of design and construction, and facilitate the identification of undermatching risk of in-service pipelines and the systematic reliability enhancement of the welding structure of high-grade pipelines.

Keywords

• high-grade steel
• natural gas pipeline
• girth weld
• strength matching
• fracture toughness
• strain concentration
• failure