Unfortunately, some types of inert gas systems actually increase the rate of corrosion in vapor spaces. The by-products of combustion in flue-gas type inert gas systems combined with higher temperatures in the area, can create a problem with acids, chemicals, etc. that can also harm the steel...
Contact the American Bureau of Shipping (ABS AMERICAS) in Houston and ask to speak to the group that handles classification rules for offshore structures and MODU's. You can find the contact info at www.eagle.org. It is highly likely the rig is classed, and needs this item approved.
There are a few good sources for this problem. One is a book called "DYNAMIC ANALYSIS OF MARINE STRUCTURES", by Muga and Wilson. There is also HYDRODYNAMICS IN SHIP DESIGN (3 VOLS) by Saunders, and "BEHAVIOUR OF SHIPS IN WAVES", by Vossers. I've also seen, but not used a few...