Laurie Crane, North Sea Oil – Saturation Diver and Film Extra
Laurie Crane – Hyperbaric Welding
Hyperbaric Welding
Hyperbaric welding is the term giving to welding when it is performed under pressure. There are two forms of this in the diving industry, “wet welding” carried out in, but unprotected from, the surrounding water, normally a non-critical weld. The other form is “habitat welding” this process is carried out Sub Sea, but in the dry, and is often the customers preferred choice when specifications required are stringent.
The most common type of welding performed within a habitat are pipeline welds, carried out on either new laid pipelines that are tied into the platforms, damaged pipelines were sections are cut out and replaced with a section of new pipe, or when an alteration is needed, such as SSIV (sub sea isolation valve) as were commonly installed after the Piper Alpha tragedy.
Habitat welding has been performed at great depths, Laurie himself was one of the hyperbaric welders on the Magnus Platform structural repair at 186 metres, over 600ft, the deepest repair of its kind to date, this was carried out by “Comex” in 1991
With specifications and criteria being high; it is normally only those divers with a welding background that get involved. The welder divers that Laurie has been fortunate to work with are all experienced & highly qualified; they execute this trade with the utmost professionalism. Encouragement and help from them have allowed Laurie himself to develop sought after skill.
Welding in the habitat is carried out using properly trained divers; first job up is the preparation of the worksite around the two pipelines to be welded. If the pipe is buried, excavation will be required, to achieve the required depth, sucking the seabed away with a huge vacuuming tool, which diver’s call an “airlift”, the excavated area is about the size of half a tennis court. Attached to each pipeline are large “pipe handling frames”, their purpose is to allow divers to manipulate the pipelines sideways for alignment, and elevate them about 2m / 6ft off the seabed, for access to the bottom of the pipe. Once all the preparatory work has been done, the welding habitat, which weighs about 60 tons, is lowered by the ships crane gently down through the depths to the work site and carefully guided over the pipelines. Because of its size and weight this awkward task is often left to one of the more experienced divers, especially so when visibility is poor or non existent.
The Habitat could well be described a huge “shoebox” with its lid missing, about the size of a flat roofed garage for a car. This “shoebox” is turned upside down (open end is now at the bottom) it has arched doorways either end, which slot over the pipelines. Clamps then secure the “shoebox” in place. Rubber seals are pulled over and fixed to the pipes and likewise to each arched doorway. The resulting seal prevents water from getting in and gas from getting out, as gas is pumped in into the “shoebox”, it displaces the seawater. The “shoebox”, habitat” is now dry, just like an upside down glass or cup in a sink or bath, air is trapped inside and can’t escape.
Now dry, the hyperbaric welders can enter “shoebox” from underneath, strip out of their diving equipment and prepare the area for welding. All the services come down from Vessel including gases for breathing, hot water for heating, communication cables and an electrical supply for power tools and the welding plant. Pre qualified and fully trained welders complete the weld to the specifications required by the client, depending on the size of pipe anything from 2-8 lads can be used to complete the whole weld, swapping out on the seabed two at a time at the end of their shift. Welds are then tested by X-ray and upon successful inspection, wrapped in a bonding bitumen tape protecting it from corrosion. The habitat is then flooded, the pipeline lowered onto the seabed, and everything including the habitat is recovered to the vessel and serviced for the next weld.