Innovative approach of mechanized GMAW procedure qualification of X65 grade S-lay offshore sour pipeline

API 5L Gr. X65 PSL2 or DNV L450 with NACE compliance line pipes are successfully being used for sour pipeline application over a long period. Subsea pipelines are mostly designed, using strain-based approaches, to operate under thermal longitudinal tensile stress levels approaching and exceeding the pipe material yield strength. From an economic pipelay perspective from offshore barges, mechanized GMAW has now been successfully used for pipeline applications for over thirty years and has achieved an impressive record in improving productivity over that time. The GMAW process, therefore, represents the current state-of-the-art and represents the benchmark against which other welding processes have been used in offshore pipeline applications. To maintain the productivity benefits of the mechanized GMAW process, especially in the sour service application, the main concern is the integrity of the butt welds made using the mechanized GMAW process. Common weld flaws found in this welding process such as lack of fusion or penetration are unavoidable which presents a concern that they may propagate by fatigue and fracture, under operational stresses, to cause hydrocarbon release. It has also been found that automatic ultrasonic testing (AUT) is the suitable Non-Destructive Testing method to detect weld defects such as lack of fusion or penetration in narrow grove bevels used in pipeline girth welding using mechanized GMAW process. Nowadays, weld integrity is confirmed by fracture mechanics analysis, called engineering critical assessment (ECA), which predicts a maximum allowable flaw size for the automated ultrasonic testing (AUT) conducted on the pipe lay vessel (barge). In order to achieve constructible ECA-based alternative flaw acceptance criteria for pipeline girth weld of the sour pipeline, it has been found that an innovative method of developing welding procedure using mechanized GMAW process for API 5L Gr. X65 or equivalent pipeline installation is a suitable constructive approach based on offshore industrial experience. In this study, the effect of several input parameters related to design, line pipe manufacturing, welding consumables, and process on welding procedure development are described and principles behind the need are covered provided based on welding procedure qualification performed.