Polymeric coatings for wireline wear and impact resistance
Polymeric coatings find applications in downhole water injector tubulars, protecting the inner surfaces from corrosion. Although these predominately epoxy-based coatings resist the harsh temperatures and pressures associated with a working injector, they are currently failing when exposed to mechanical damage. The mechanical damage takes the form of impact and wireline wear inflicted by the downhole 'tools' required in the maintenance of the injectors. In this work, experimental techniques have been developed for the successful direct observation of the impact and wireline wear damage mechanisms. The work has taken two concurrent paths, one investigating the abrasive wear range of supplied polymeric coatings utilising a pin-on-disc rig, the second studying the same coatings under impact conditions for which a specialised rig was designed and built. By comparing the recorded failure mechanism to physical properties of the coatings, relationships were found which led to recommendations initiating compositional changes to the coatings. One of the most significant findings of the work was that although the downhole coatings industry has spent many years developing and marketing thermoset based coatings, the under-utilised thermoplastic-based coatings appear to offer a 'better' solution to the problem. Unlike the modified epoxy coatings, it was shown that nylon-based coatings resist both wireline wear and impact damage without compromising the corrosion barrier properties of the coatings.