Hydraulic cylinders are used for many vital applications on offshore installations. For the long stroke cylinders used in the direct acting riser tensioning application the piston rod surface is exposed to severe degradation; combining corrosion, wear and mechanical stress. Direct acting riser tensioning systems are often used during ultra-deepwater offshore drilling, when exploring for oil and gas. These direct acting riser tensioning systems usually consist of 6 long stroke hydraulic cylinders located at the splash zone level. These cylinders ensure constant tensioning of the drilling riser as the drilling vessel is operated in ultra deep waters up to 3000 meters compensating for heave due to sea waves and tide. The direct acting tensioning systems have been in operation since the late 1990’s, but the system integrity and service life has so far not been acceptable. Operational experience shows that the thermal sprayed coatings applied on these piston rods have dramatically shorter life than predicted by qualification tests programs. The consequence of the failing rod surface is sudden coating damage such as pits and flaking which further damages the seals in the packing flange. As a result hydraulic oil leakages occurs, thus polluting the environment and in the worst case leads to loss of the tensioning in the riser causing subsequent drilling down time and eventual riser breakage and blowout. This paper will provide a generic summary of operational experience, development and degradation issues of direct-acting riser tensioning cylinder piston rod surfaces. Several case histories are included to highlight piston rod failures and an evaluation of alternative concepts to improve service life of piston rods is given.

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