Testing of High Corrosion Resistant Metallic Coatings for Tensioner Risers and Piston Rods Exposed to Marine Environments

摘要

Hydraulic riser tensioners (for offshore drilling platforms) and piston rods (for hydraulic systems) have been extensively used in marine environments. They are exposed to a wide variety of severe operating conditions that range from marine atmospheres to splash zone in brackish and saltwater.The present work describes a novel testing methodology, based on the Zero Resistance Ammeter that allows the determination of the Critical Pitting Temperature (CPT) as well as the Critical Crevice Temperature (CCT) in small angular sectioned samples taken from cylinders (tensioner risers and piston rods). The determination of the CPT and CCT allows the pre-screening of various materials and alloys for their use as piston rods. Several materials and alloys have been successfully pre-screened using this testing methodology combined with metallurgical analysis.Of particular interest, a part of the sample may undergo crevice corrosion while the sample is being tested, whereas the rest of the sample will remain intact. As the temperature is further increased, pitting corrosion can take place in those passive areas that have not undergoing crevice corrosion.