Double jointing is an effective approach for pipeline construction in terms of both welding productivity and consistent weld quality as a result of a controlled working environment. However, the high heat input associated with the submerged arc welding (SAW) process used for double jointing must be considered with respect to the material properties of both heat affected zone (HAZ) and the weld metal of double jointing welds. This is particularly important for strain-based design pipeline applications utilizing high grade pipe, such as X80 and X100. High grade pipe materials achieve their strength as a result of controlled rolling practices that produce a fine grained steel. High heat input welding results in an increased grain size in the heat-affected zone, and often results in softening and a detrimental effect on the properties of the welded joint. The softening effect in the HAZ will potentially cause highly localized deformation, which is undesirable in conditions where strain-based design is applicable. Understanding the material mechanical property in double jointing welds, and approaches for measuring mechanical behavior of such welds are required in order to meet the increasing demand for double jointing in the pipeline industry. This paper presents an approach that has been used in TransCanada for understanding and evaluating double joint welds of high grade pipes. The approach has been implemented into detailed testing protocols, data analysis procedures and requirements, and has been proven to be an effective and practical means for double jointing evaluations.

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