Water-glycol solutions (HFC) [1] are one of the most commonly used hydraulic fluids in applications where fire hazard is a concern such as in the offshore oil industry. However they may cause corrosion failures of components in electro-hydraulic control systems that can have serious consequences for the operation of an entire subsea oil recovery system. The principal objective of this study is to assess the corrosion behaviour of the main material of construction used for the components in such systems (Stainless Steel 316L) in a range of commercial water-glycol hydraulic fluids (Oceanic HW443, HW525, HW540, HT, EE1), and to find out the probable factors that may affect the corrosivity of each fluid.

The corrosivity of each fluid was ranked according to the breakdown potential obtained from cyclic potentiodynamic polarization (CPP) tests [2]. Gas chromatography-mass spectroscopy (GC-MS) analysis was carried out to assess the components of the different organic additives in each fluid and the water percentage of each fluid was determined by Karl Fischer titration. A comparison of relative ethylene glycol content has indicated that the higher the concentration of ethylene glycol the more corrosive the fluid is to stainless steel 316L if the additive package is the same. However, additive packages dominate the corrosivity.

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