Wear resistance of the pressure armor submitted to deep cryogenic treatment and plasma nitriding

Abstract

Risers are multilayer structures used in oil production and transportation. The pressure armor is the layer responsible for supporting the internal radial pressure and is produced from a helical interlocked steel wire. The interlocking mechanism, which gives flexibility to the riser, is responsible for the wear on the pressure armor, resulting in a micro-abrasive wear. The present work aims to study the effect of deep cryogenic treatment and plasma nitriding on the micro-abrasive wear in the pressure armor. Samples tested were taken from the contact region of the pressure armor. The micro-abrasive wear test was performed on a free ball machine. The tests were conducted on the samples as received, with deep cryogenic treatment and with plasma nitriding (at 515 °C for 8, 24 and 48 h). It was observed that the material with deep cryogenic treatment had a Vickers microhardness profile and wear coefficient similar to the sample as received. The nitrided samples showed a higher (21.8%, 23.2% and 29%) microhardness value at the surface region than the sample as received and an improvement in wear coefficient in the transient (29.85%, 28.53% and 29.81%) and permanent (19.18%, 25.19% and 28.09%) regions.