Main problems and countermeasures of girth welds of oil and gas pipelines

Abstract

In order to solve the problem of girth weld failure of high-grade pipelines and improve the safety of oil and gas pipelines in China, the influencing factors of girth weld failure of pipelines were systematically analyzed. It was found that the girth weld failure of pipelines was resulted from the combined action of the additional loads, defects, performance degradation and strain concentration. Meanwhile, the strain concentration in girth welds was mainly led to by the unequal wall thickness, including the misalignment caused by the geometric dimension of steel pipelines, and the low strength matching due to the welds or softening of the heat affected zones. In order to improve the bearing capacity of girth welds and reduce their strain concentration, a new type of pipe design idea was put forward, with the high dimension accuracy, out-of-roundness and circumference difference at the end of the pipes, as well as the misalignment of girth welds and the joint clearance during butting, close to zero, solving the current problems of misalignment and unequal thickness caused by the geometric dimensions at the end. In addition, by increasing the end thickness of pipes and using the principle of structural reinforcement, the stress bearing capacity of girth welding joints can be greatly improved, and thus the problem of low strength matching caused by the girth welds or softening of the heat affected zone could be solved, so that no or little plastic deformation occurs at the girth welding joints and the safety of the girth welds of pipes is improved significantly.

Keywords

• oil and gas pipelines
• girth welds
• pipeline safety
• strain concentration
• low strength matching
• structural reinforcement