Welding: Hyperbaric Welding

Abstract Hyperbaric welding is used for different steels in many underwater applications as a repair welding process. A difference between wet and dry welding processes can be made. Due to the increased ambient pressure, these processes have special features inherent in the process that influence the cooling and penetration behaviour. The positive use of these effects outside underwater applications is currently rarely addressed in science and application. The presented work establishes these advantages on the basis of a higher strength structural steel and characterizes the effects on the microstructure of a joined S700MC steel and on the mechanical properties of the joint. It will be shown that a hyperbaric environment can be used to orient the weld more towards the depth of the sheet. Furthermore, it will be shown that this change leads to modified cooling, which in itself influences the mechanical properties of the weld seam.

Offshore structures are typically subjected to high dynamic loads, such as wind, waves, flows, impacts in high seas and vibrations from auxiliary machines. Additionally, apart from the complex operating loads, climatic influences and the corrosive effect of seawater combine to strongly impair the operational behavior of the structures. For these reasons, high demands regarding the quality of welded joints are being made that primarily must satisfy the required ultimate strength values in underwater structures. Thus, in deep water, computer numerical controlled (CNC) welding equipment for high-quality and reproducible weld seams is necessary.

Defence support specialist DML, based at the Royal Navy's Devonport dockyard, has now succeeded in wet-welding two high-strength steel grades used in submarines, and believes the technique can be extended to other underwater structures such as pipelines and oil rigs. But wet welding isn't just welding underwater - it's manual arc welding without anything to protect the metal, such as a hyperbaric chamber. DML has been working on the problem because of the need to decommission nuclear submarines. Wet welding techniques allow this to be done with the submarine in the water, removing the need for dry-docking.