Recently, the industry has identified several new construction girth welds that have failed within the first few years after construction. Despite the welding procedures used in these situations meeting industry standards, these failures occurred as a result of traditional welding techniques being applied to stronger, more advanced line pipe base material. As such, the girth welds were undermatched, and the heat affected zone (HAZ) displayed high levels of softening.

David Futch, who presented findings on these girth weld failures at the 2021 API/AGA Joint Committee on Pipeline Welding Practices, is the Director of Materials Engineering at ADV Integrity. He said, “One of the problems facing operators in these situations is that the current techniques used to qualify welding procedures produce a limited understanding of what is actually happening in and around the welding site.”

Mr. Futch argues for two supplementary testing alternatives for qualifying welding procedures and, consequently, mitigating risk. One is Digital Image Correlation (DIC) of cross weld tensile specimens that provides more accurate information about the accumulation of strain in these welds. DIC provides a visual representation of where the strain is concentrated, which results in a clearer understanding of the failure mode of the weld.

Figure 1: DIC of tensile showing failure in the base material as the strain develop away from the girth weld

Mr. Futch’s second recommendation is performing sub-load hardness testing maps along the weld’s cross section, which visualizes the relative strength in a sample. Sub-load hardness testing maps and the associated color outputs helps visualize the softening of the heat affected zone much more accurately than traditional methods.

Figure 2: Hardness profile shows minor softening in heat affected zone (HAZ) even though weld is evenly matched with pipe

“For qualifying procedures on high strength material, operators can gain a better understanding of the risks associated with welding by running DIC of cross weld tensile specimens and fully automated hardness maps. As a result, you’ll confirm that your procedures help mitigate these early girth weld failures,” added Mr. Futch.

Much in the same way magnifying glasses make clear what was not visible before, the combination of these two tests allows for much more accurate assessments of welding procedures. Where traditional techniques may fail to pick up on key indicators of potential failure, DIC of cross weld tensiles and hardness testing can produce clear and accurate assessments. In addition, these processes are not limited to girth weld qualifications. The applications of these tools could be applied to a wide range of assessments for better pipeline protection.

“For a marginal cost, operators could see a large return in terms of asset protection and risk mitigation if they supplement these two techniques to their qualification procedures,” Mr. Futch said. ADV Integrity is fully equipped and ready to perform these assessments at its test facility in Waller, Texas.

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