Client’s offshore PRT cylinders needed repair due to leaking rod and piston seals. To perform this work the cylinders need to be removed however the holding pins were stuck. Previous removal attempts with 50 ton jacks did not remove any pins.
RNMT’ was asked to provide engineering, equipment, and personnel to remove the 4.5 inch diameter pins from the offshore production riser tensioners. The client desired a solution which did not require a hot work permit so that oil/gas production could continue during pin removal work. The pins were located in the well bay with limited free space. Once removed, RNMT was asked to provide replacement pins.
RNMT’s plan included three options which met the client’s desire for a no hot-work removal solution. The options were successive in effort and time which minimized the offshore work costs. In Phase 1, RNMT designed a custom fixture to apply jacking force directly to the pin. During Phase 2, RNMT utilized the fixtures from phase 1 to hold a hydraulic powered drill to allow tapping the pin head side of the pin. Once tapped a larger pulling jack could be installed. This phase allowed pulling and pushing jacks to apply 110 tons of removal force directly to the pin. Finally, in Phase 3, if the pin was not removed, RNMT utilized a 55,000 psi water jet cutter to cut the pin in half. The fixtures already installed from phase 1 were designed to hold the cutting head which guided the cut.
Engineering & Testing the Solution
RNMT modeled the surrounding structure in 3D CAD to insure the solution fit into the space constraints. Considering all phases, a set of fixtures were designed to accommodate push jacks, pull jacks, hydraulic drill attachment, and holding the water jet cutting nozzle.
RNMT manufactured the required fixtures and supplied all tooling required to complete all phases. Prior to mobilizing equipment offshore, RNMT tested all phases onshore.