Pipelines may experience significant longitudinal strains when subjected to large ground motions, such as seismic activity, landslides, etc. For these conditions, a strain-based design (SBD) approach can be used. The use of higher strength steels (like X80) for SBD approach can enable significant construction cost savings. Costs can be further reduced through the use of a double jointing process in order to reduce the amount of field welding. However, it is challenging to achieve adequate girth weld properties for SBD scenarios involving higher strength steels by using conventional double jointing processes such as submerged arc welding (SAW).
Acicular ferrite interspersed in martensite (AFIM) has been previously identified as an advantageous high strength weld metal microstructure that can be applied in field pipeline construction. In this paper, a double jointing technology for X70+ SBD applications will be discussed. Excellent strength and toughness properties were achieved in double joint welds by using an optimized AFIM welding technology that included a tailored welding consumable wire and a high productivity GMAW-P weld process. Welding procedures are discussed along with mechanical properties achieved. Productivity comparisons suggest that a fully optimized GMAW-P welding process in the 1G-rolled welding position can have productivity comparable to a conventional SAW double jointing process.