Study of the Corrosion Behaviour of Nickel Tungsten Carbide in Some Water-Glycol Hydraulic Fluids for Subsea Applications

Corrosion failures of components in electro-hydraulic control systems can have serious consequences for the operation of an entire subsea oil recovery system. An acceptable reason for this is that seawater ingress can have a great effect on stainless steel 316L, the most commonly used material for the failed components of the direction control valves, since chloride irons are known to destabilize the passive film. Another material, Nickel Tungsten Carbide claimed to be seawater tolerant, has been used in this system. However, problems still exist due to the complex factors relating to the corrosion process and how the environmental parameters affect the corrosion mechanisms. In this work, the corrosion behaviour of a Nickel Tungsten Carbide cermet is compared with stainless steel 316L, in four different water-glycol hydraulic fluids and 50% fluid/50% seawater solutions using an electrochemical test methodology. Detailed conclusions are then made to summarize the advantages and the disadvantages of nickel tungsten carbide to be used in this system. The effects of each factor on the corrosion rates and mechanisms are discussed. Keywords: Nickel Tungsten Carbide, Stainless Steel 316L, hydraulic fluids, corrosion.