The effect of fillers on the wear resistance of thermoplastic polymeric coatings

Thermoplastic polymer matrix composites are used as coating materials for t he bore of downhole tubulars used as water injectors in the oil industry. T hese coatings are primarily employed for corrosion resistance but must also resist mechanical damage from the inspection tools lowered at speed down t he tubing. This mechanical damage is produced by the wearing action of the supporting wire against the coating (wireline wear) and by direct impact of the tool against the coating. Filler materials are added to these polymeri c coatings and these additions are known to affect the wear resistance of t he coating. In this study, three types of thermoplastic polymeric coatings were subjected to wear tests. Both abrasive wear tests - using silicon carb ide papers as the abrasive, and wireline wear tests, utilising a true tribo couple consisting of the coating and a length of "slickline" wire on a modi fied pin on disc apparatus - were carried out to study the wear resistance of these three coatings. Detailed scanning electron microscopy was performe d on the wear tracks produced to elucidate the wear mechanism and in partic ular the role of fillers. In abrasive wear a polymer with a brittle filler has a higher wear rate than an unfilled polymer due to the fact that the br ittle fillers can be easily fractured and detached from the polymer matrix. In general, the weak bond between the filler and a thermoplastic polymer m atrix leads to the filler particles detaching from the matrix causing enhan ced wear. In wireline wear the presence of voids and unmelted particles is particularly deleterious. (C) 2001 Elsevier Science B.V All rights reserved .