A fundamental rule of welding engineering is that, in general, the strength of a weld should be greater than the strength of the base materials being joined. In the past, little difficulty has been experienced in meeting this fundamental rule during construction of cross-country pipelines. As the use of higher strength line pipe material has increased, overmatching the strength of the base material with the weld has become more challenging, particularly when the girth welds are made manually using cellulosic-coated electrodes. A number of girth weld failures in newly-constructed pipelines have occurred in North America recently, either during pre-service hydrostatic proof testing or soon after being placed in service. Some of these failures have been attributed to construction quality issues, while others have simply been the result of undermatching strength and/or heat-affected zone (HAZ) softening in what would otherwise be considered “acceptable” girth welds. Strength matching requirements for pipeline girth welds in industry codes and standards will be reviewed as will contributing factors to some of the recent failures. The importance of ensuring adequate strength so that axial strains do not accumulate at pipeline girth welds will be emphasized.
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