Hydra-Lok® Caisson Repair System

Severe localised corrosion frequently occurs on seawater pump caissons on offshore platforms. The caisson corrodes in an area adjacent to the pump and is usually associated with galvanic action between the pump and the carbon steel caisson. The damage caused may be so extensive and severe that it eats completely through and severs the caisson.

The severed caisson leaves the pump unprotected and reduces its efficiency. There is also the possibility that the severed piece of caisson in falling to the seabed will damage the surrounding structural members of the platform. It may also damage pipelines or other equipment on the seabed beneath the platform.

Traditionally the solution has been for divers to fix a split clamp externally around the caisson, an operation carried out from a dive vessel and requiring good weather. Since 1996 Oil States MCS have been repairing caissons by cold forging an internal liner using the Hydra-Lok® swaging system. The liner bridges the area of corrosion and supports the lower part of the caisson.

An internal survey using a camera and/or ultrasonic probe is carried out to determine the extent of the corrosion damage. A plain liner is designed such that it will pass internally through the caisson with the minimum of clearance. It is long enough to bridge the area of corrosion and overlap onto undamaged caisson either side. The swaging operation is then performed using a Hydra-Lok® tool to expand the liner into the undamaged caisson above and below the damage.

Oil States MCS, 18501 Aldine Westfield, Houston, TX 77073. Tel: 281-821-8600; Fax: 281-821-2463.