Study of the corrosion behaviour of Nickel Tungsten Carbide in some water-glycol hydraulic fluids for subsea applications

摘要

Corrosion failures of components in electro-hydraulic control systems can have serious consequences for the operation of an entire subsea oil recovery system, especially in water depths more than 150 metres. One 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 ions destabilize the passive film. Other materials, claimed to be seawater tolerant, are starting to be used in this system. However, problems can 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 (NTC) 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 NTC to be used in this system. The effects of each factor on the corrosion rates and mechanisms are discussed.