Remotely controlled subsea welding is often required for pipeline repair and hot tapping where pipelines are installed in water depths beyond acceptable diving depths. The present investigation concerns the development of hyperbaric gas metal arc welding of X65 steel. Welding was carried out at 12–35 bar with low alloyed steel and Inconel 625 wires. All welds gave overmatch situation with respect to strength. Toughness requirements at −30°C were also satisfactory met, although the Charpy values tend to be close to the minimum required individual values of 40J due to high oxygen and fairly high nitrogen contents. The Inconel 625 weld metal toughness was very high. This was also the case for the fusion line toughness for both wires.
The North Sea network of offshore pipeline transportation systems for natural gas is the world largest, comprising more than 6000km only on and from the Norwegian Continental Shelf (Berge, 2005a). For the large diameter pipes hyperbaric welding have been the dominating joining technology. This technology is now prepared to do remote operated (no need for diver intervention) pipeline repair. Ongoing development programs will push the technology further to cover 44" pipelines as well as smaller dimensions down to 4" and water depths to 1000 – 2000 meters pending on the actual need (Berge, 2004). Moreover, development of remote operated tooling systems for hottapping is ongoing. In fact, the present investigation is part of the development of robust gas metal arc (GMA) welding technology to be used in future diverless, remote controlled tie-in and hot tap welding. It will be shown that excellent mechanical properties are achievable.
The base metal used was API X65 pipeline steel. Two types of filler wires were applied; one low alloyed metal cored wire supplied by ESAB, denoted HBQ Coreweld, and one solid Inconel 625 wire.
