Pipeline Construction Practices Risk Assessment Methodology

This paper examines how changes to pipeline construction specifications/practices can impact both technical and economic considerations of the overall project. The main topics of concern fall under the general headings of joining design, welding, and nondestructive examination (NDE). The different options for the project-specific construction specifications include a discussion of recommended construction practices, and includes an assessment of the risks associated with the different construction alternatives. The following six specific issues were considered significant to the risk of construction-related issues and these were the focus of this scope of work: • Assess the design requirements for joining pipe with different wall thickness, and specifically the use of counterbored and tapered transition pieces; • Examine the impact of specific welding-related construction activities such as release of internal line-up clamps used for welding; • Examine the need for hot pass deposition before removing the internal line-up clamp; • Examine the delay time between weld passes and the total time to complete each weld; • Investigate delay time before completion of weld NDE; • Consider the differences between the use of gamma and x-ray NDE, and the likelihood of detecting weld flaws. A semi-quantitative risk assessment methodology has been developed to calculate the likelihood of failure from planar defects in girth welds. The failure frequencies of girth welds have been based on industry experience, and combined with the likelihood of detection using nondestructive examination techniques, it is possible to show the likelihood of failure during either hydrostatic testing or subsequent service of the pipeline. The results of such an analysis can be used to evaluate the risks associated with changes to construction practices along the pipeline right-of-way.