Offshore cutting and dismantling is usually undertaken as a result of decommissioning work on oil and gas platforms. In the UK this generally means in the North Sea. Because of the highly volatile nature of oil and gas and the potential dangers associated with working in such an environment, any offshore cutting operations have to be undertaken with the greatest degree of care and attention to safety.
Decommissioned materials are often of high quality steel, which makes their recovery desirable. This means that heavy structures need to be dismantled then cut into sizes suitable for transportation to onshore sites. Heavy lifting equipment may be required, along with the trained personnel to operate it safely and efficiently.
Subsea infrastructures have their own special challenge as regards cutting and dismantling. Thermal drilling and flame jet cutting methods may be employed to good effect. Offshore cutting and dismantling techniques have evolved over the years to provide the industry with efficient strategies that combine safety with cost efficiency.
Where there is likely to be a risk of explosion from combustible gases, as is certainly the case offshore on oil and gas platforms, any cutting required must be done in such a way as to eliminate any chance of a spark that might ignite gases. It goes without saying, that most common types of cutting appliances are not suitable.
The answer to this dilemma is cold cutting using high pressure or ultra high pressure water jets – sometimes containing a sharp edged abrasive. The water is mixed with the abrasive material and forced through a fine nozzle at extremely high pressure and speed, producing an amazing cutting force, perfect for locations, like oil rigs, where safety from fire or explosion is of paramount importance. It sounds simple, but this technology can slice through high strength steels, even when the steel is up to 30 centimetres thick! The lack of heat produced means the material being cut doesn’t get distorted.
Cold cutting can also effectively cut through reinforced concrete without creating a single spark, making it the ideal tool for offshore cutting and dismantling operations. Concrete up to one metre in thickness can be sliced through with little effort leaving a clean cut face.
Cutting and dismantling of pipes and equipment can be a hazardous job without proper care and attention. Using water abrasion suspension jet cutting means that the task can be performed remotely, thereby making the entire operation much safer for all the personnel involved.
Special handling is required when working with materials where oil has been in transit. Spills must be kept to a minimum, with procedures in place to deal with any unexpected situation that may arise during the operation.