Methodology to Identify Potential Sites for Susceptibility to Low Strength Girth Weld Behaviors

Abstract Since 2000, numerous instances of field girth weld failures have led to product releases, attributed primarily to the difference between weld metal strength and unexpectedly high base metal strength or significant softening in the heat-affected zone (HAZ). These causal factors often result in girth welds of lower strength, prone to failure at low global strains, near the actual material’s yield strength. These results indicate that external loads alone are not the primary cause of through-wall failures. The documented failures consistently reveal that the presence of low-strength girth welds substantially contributes to these failures, despite meeting welding code requirements. In response, operators started conducting engineering assessments to evaluate the risk associated with low-strength girth weldments in the existing pipelines. Performing detailed engineering assessments on every pipeline weld is not feasible. Hence, a comprehensive screening engineering assessment has been developed to evaluate the risk each girth weld poses systematically, incorporating metallurgical, girth weld, and structural considerations. Metallurgical analysis involves assessing pipe grade and manufacturing year to gauge HAZ softening and potential weld metal strength undermatching. Girth weld assessment focuses on the weld metal’s strength, influenced by heat input during welding and the use of low-strength electrodes, alongside quality assurance measures such as in-field parameter monitoring, test welds, and historical performance. Structural considerations include potential exacerbating factors like weld misalignment, thickness transitions, and external load sources. This integrated approach has proven effective in identifying vulnerabilities to failures associated with low-strength girth welds, including undermatching and HAZ softening. The paper presents a case study applying this methodology to an operational pipeline, demonstrating its utility in preemptively identifying and mitigating risks associated with girth weld failures.