Premature Failure of Riser Tensioner Piston Rods Exposed to Offshore Splash Zone Operation – Status and Review of Critical Multi-Degradation Factors

This paper reviews the experience, development and degradation issues of direct-acting riser tensioner cylinder piston rod surfaces. A hydraulic cylinder used in a direct-acting riser tensioning system on board a deepwater drilling vessel operates in the splash zone, thus working in an extremely harsh environment. The piston rods are exposed to a corrosive environment in combination with continuous wear action and high static and cyclic mechanical loading. Operational experiences show that the coatings on these piston rods have dramatically shorter life than expected. The goal is to improve the service life of these piston rods. This will be achieved by establishing fundamental knowledge about the combined effects of corrosion, wear and fatigue degradation of selected tribological/piston rod surfaces. The experience survey information shows that the plasma sprayed coatings are performing poorly, also the HVOF cermet coatings similarly poor on stainless steel substrate. The experience input data indicate how operational factors and properties of material combinations affect the total degradation.

Previous research and qualification have focused on standardized testing methods, mainly verifying the ability to withstand each of the degradation mechanisms alone. The paper will also discuss the development of new test methods and testing regimes to determine the real deterioration.