Selection of Conversion Layer Applied Beneath Thread Lubricant Coating

Abstract

A polymer coating is often used instead of lubricant in order to protect the threaded part of an oil pipe fitting. There are several forms of these coatings of different composition applied by spraying to the threaded element of a pipe. Metal surface preparation before coating application has a considerable effect on polymer coating quality. Conversion coatings that formed on a pipe threaded surface and couplings as an intermediate layer between a metal surface and a polymer coatings are analyzed. The conversion coatings selected are various phosphate coatings and an alternative phosphate-free zirconium coating. Comparative study of these coatings includes an analysis of application technology, a study of conversion coatings physicochemical properties, and comparative tests for a conversion coating – thread lubricant coating system.