Preventing Girth Weld Failure in Pipelines: Measurement of Loads and Application of Assessment Methods

Abstract

Abstract Pipeline failures from circumferential cracking at girth welds continues to affect large diameter oil and gas transmission lines, even for modern lines constructed this century. The key factors that contribute to the failure at girth welds are the dimensions of defects present, the material properties of the pipe and weldments, and the presence of loading that drives crack growth. The mechanisms of failure are well understood, but identifying and measuring the contributing factors can be a challenge. Locating girth welds that are subject to elevated loads will enable operators to focus on sections with an increased threat of failure. In this paper, we consider each of the key factors, how these are identified and defined, and the uncertainties in the measurement process. Specific attention is applied to the presence and quantification of loads and how these influence the potential for failure. This includes sources of active external loading due to ground movement, for example, or loads generated in the pipeline from the construction process. Loads can also be quantified by measuring bending strain from inline inspection inertial measurement units. A more complete picture of pipeline loading can be established by integrating a structural analysis that accounts for the direction of pipeline movement and the presence of axial loads. The relationship between assessing pipeline integrity from ground movement — typically with strainbased methods — and establishing whether the defect can survive the load is explored. The relative contribution of bending and axial loads in the failure of defects is considered. The outcome of the study will assist pipeline operators in prioritising actions that enable the quantification of the all the key parameters. The resultant analysis will provide guidance on the girth welds that have an increased risk of failure and this will enable protective actions to be defined and scheduled accordingly.