Hard Spot Management Framework for Gas Transmission Pipelines Using Risk-Based Approach

Abstract The presence of hard spots can be a concern for gas transmission pipeline integrity management because these manufacturing defects might fail under normal operational stress. Considering pipeline failures associated with hard spots and increasingly stringent regulatory requirements, there is a need for pipeline operators to establish a robust and efficient hard spot integrity management program. Currently many pipeline operators use industry susceptibility studies conducted in the early 2000s as a basis for their hard spot integrity management program. These studies identified that susceptibility to the hard spot threat is mostly associated with a specific pipeline steel plate manufacturer. However, these studies were limited by incomplete failure data, and lack of length-normalization, rendering them inadequate for comprehensive reliability and risk analysis. A systematic review of existing hard spot data and recent study performed by Pipeline Research Council International (PRCI) MAT-7-2 project suggests susceptibility to hard spots across a broader range of manufacturers and operating conditions. Herein, this paper discusses operators’ experience with the hard spot threat outlining learnings, findings, and challenges. Then, this study employs PRCI MAT-7-2 susceptibility criteria, integrating them with field verified-findings and operators’ experience to guide informed decisions in the pre in-line inspection stage, with the goal of establishing future inspection plan. This is achieved using a flexible Bayesian Network approach that captures uncertainties and interdependencies offering a more comprehensive solution than relying on traditional deterministic susceptibility guidelines. Next, the study extends to a post in-line inspection review of hard spots, using a risk-based approach to mitigate potentially injurious features. To accomplish this, the study leverages a structural reliability methodology using a hard spot failure pressure model applied in a Monte Carlo simulation. Such approach helps to rigorously account for uncertainties and quantify the probability of failure, considering essential factors such as ILI measurement error, pipe material properties, hard spot dimensions and hardness, etc. An operating scenario study is included to demonstrate the practical application of the proposed framework in effectively managing the hard spot threat in gas transmission pipelines.