Grooving micro-abrasion of polyamide 11 coated carbon steel tubulars for downhole application

The tribological properties of polyamide 11 coated carbon steel injector tubulars are reported using a commercially available micro-abrasion tester, as a candidate method for assessing the abrasive wear of polymer coatings. Efforts have been made to reproduce the wear mechanisms found to predominate in field simulated conditions. The wireline-based tests produced severe grooving abrasion of the polyamide 11 coating resulting from contact between the spherical capped wireline asperities and the coating. Scanning electron microscopy (SEM) confirmed that grooving wear mechanisms were generated in the micro-abrasion tests and were due to micro-ploughing by the hard silicon carbide abrasives. To better reproduce wire-on-tubular contact conditions, a series of micro-abrasion tests using 6 μm spherical glass beads were also performed, but bead embedment complicated their interpretation. Test parameters such as load, sliding distance, sliding speed, abrasive morphology and type were found to significantly affect the wear rate of the coating. Comparison between the results of monolithic and coated polyamide 11 show that the coating generally out-performed the monolithic polyamide 11, possibly linked to enhanced coating properties induced during deposition. The wear rate of the coating was found to vary as a function of crater depth, increasing at a depth of 50 μm indicating the presence of a hard surface layer. Overall, the micro-abrasive wear test has reproduced a similar mechanism to that exhibited by wireline tests. Thus, the micro-abrasive test can be used as an accelerated wear test to investigate the tribological performance of coatings for tubulars.