Welding Procedure Qualifications of Girth Welds Suitable for Actual Field Conditions

Abstract There have been a number of notable incidents of girth weld failures in newly constructed pipelines in North America, South America, and Asia. The primary technical contributors for the incidents examined in North America have been identified as (1) weld strength undermatching, (2) heat-affected zone (HAZ) softening, and (3) elevated stress/strain in the affected girth welds. To make robust girth welds and avoid aforementioned incidents, a few key modifications for improving girth welding procedure qualification are proposed. These modifications address systemic gaps in industry practice, such as the lack of linkage between actual pipe properties and welding procedure qualification requirements. A few key components of these modifications are: 1. Selection of Pipes for Welding Procedure Qualification: To mitigate the negative effects of potentially high levels of weld strength undermatching and HAZ softening, it is proposed that project pipes be selected for welding procedure qualification. The selected pipes should target the upper end of the anticipated or actual strength distribution and the lower end of the Pcm and carbon distributions when possible. If a selection by pipe strength is not possible due to the unavailability of project pipes at the time of welding procedure qualification, an alternative is to develop a library of weld metal strengths through all-weld-metal tensile tests or hardness surveys for different welding processes and consumables prior to a construction project. 2. Welding Procedures: Operators or welding contractors frequently use previously qualified procedures to make new welds as permitted by relevant standards. When full qualifications are not performed on project pipes, validation welds could be made on project pipes. These welds can be made in conjunction with welder qualification for a given project. When establishing welding procedures, consideration should be given to defining limits to maximum heat input and the maximum interpass temperature to ensure the procedure is appropriate for the strength and HAZ softening of the linepipes to be welded. 3. Qualification Tests and Requirements: Cross-weld tensile (CWT) tests typically required in girth welding procedure qualification. The CWT tests may be conducted without or with instrumentation. For non-instrumented CWT tests, the requirement is that no failure in the weld region is permitted. Instrumented cross-weld tensile (ICWT) tests are designed to evaluate the performance of girth welds by examining the relative strain accumulation between the weld region and the base pipe. The tests capture the combined effects of weld strength undermatching and HAZ softening. Compared with the traditional CWT tests, ICWT tests provide much more information that allows for more in-depth understanding of the weld behavior. The qualification requirements may be adjusted for targeted applications. 4. Alternative weld strength criteria: besides CWT tests, all weld metal tensile tests can be conducted to confirm weld strength. A qualification requirement could be that weld strength must be higher than the pipe’s specified minimum strength by a sufficient margin. 5. Circumstances Not Needing the Above Qualification Requirements: Girth welds that are not expected to experience strains beyond 0.2% or stresses beyond 90% SMYS, such as welds within compressor or pump stations, may be exempted from the above recommended qualification requirements. In such cases, the requirements for weld strength undermatching and HAZ softening can be relaxed.