Quality of Electroless Ni-P (Nickel-Phosphorus) Coatings Applied in Oil Production Equipment with Salinity

Abstract

The corrosion resistance of nickel-phosphorus (Ni-P) coatings and their mechanical properties in seawater have led in- vestigations into the development of new technologies and the replacement of some special alloys in equipment used in oil production, such as valves, tubing, sucker rod joints, pumps, riser, manifolds and subsea Christmas trees. These studies began with Brenner and Riddel who developed, in the 1940s, formulations for Ni-P deposition on carbon steel without using an electric current. Joint deposition of nickel and phosphorus on a metallic surface (carbon steel) without applying an external current is accomplished using cathodic reduction with hydrogen (H) from a reducing agent (so- dium hypophosphite) and nickel salts. To assure good performance of a Ni-P coating, the deposit quality must be in- spected and evaluated during the chemical deposition process or in the end product. The recommended test parameters are: thickness, layer uniformity, hardness, adhesion, porosity, corrosion resistance and chemical composition of the nickel-phosphorus coating. The purpose of this paper was to investigate the Ni-P coating process, to evaluate the be- haviour of Ni-P in a saline environment using aqueous brine (3.5% - 30% sodium chloride by mass) and to present pos- sible defects that could compromise the coating.