Hyperbaric Welding is the process in which a chamber is sealed around the structure to be welded, and is filled with a gas (commonly helium containing 0.5 bar of oxygen) at the prevailing pressure.

The hyperbaric welding may be one of two types:

A) Mini-Habitat welding - makes use of a small, easily portable, gas-filled, often plexiglas enclosure, which is placed over the joint by a diver. Water is displaced by an inert gas or air supplied from the surface. In this instance welding is performed at elevated ambient pressures. Depending on the size of the enclosure, the diver is partially immersed in water (only the diver's hands and the welding torch are inside the habitat). This method requires adequate visibility and is limited to areas with clear access. The diver/welder welds with each of several MMA electrodes, positioned in advance through the flexible port.

B) Large Habitat welding - a specially designed chamber is built and positioned around the intended weld and the welder/diver enters the chamber in order to undertake the work. The habitat is sealed and water is excluded by introducing an appropriate gas.

Hyperbaric welding produces high-quality weld joints that meet X-ray and code requirements. Most welding processes can be operated at hyperbaric pressures, but all processes suffer a reduction in capability and efficiency results as the pressure increases. Hyperbaric welding, using MMA (SMA), TIG (GTA) or FCAW, is the preferred process for high integrity welds, particularly for deep water welds, including tie-ins in pipelines and risers in the oil and gas industries, however GTA is the method most commonly employed for hyperbaric welding operations.

Advantages:

• Welder/Diver Safety – In the case of large habitats, welding is performed in a chamber, immune to ocean currents and marine animals. The warm, dry habitat is well illuminated and has its own environmental control system (ECS).

• Good Quality Welds – Hyperbaric welding has ability to produce welds of quality comparable to open air welds because water is no longer present to quench the weld and H2 level is much lower than wet welds (prone to hydrogen cracking).

• Surface Monitoring – Joint preparation, pipe alignment, NDT inspection, etc. are monitored visually.

• Non-Destructive Testing (NDT) – NDT is also facilitated by the dry habitat environment.