Scaling and macro-fouling experienced by seawater cooling system components aboard U.S. Navy ships results in extensive downtime and manpower expenditures. Previous research conducted by the Naval Research Laboratory in Key West, FL (NRLKW) determined that cleaning of copper-nickel with descaling solution does in fact remove the passive/oxide film, which naturally forms in flowing natural seawater on these alloys. However, this does not result in significantly higher corrosion rates and the passive/oxide film?s regrowth is not obstructed.
The current research was to determine the effects of both hydrochloric acid and phosphoric acid-based solvents on titanium alloys in the freely corroding, crevice, and galvanically coupled conditions. As well as nickel alloys in the freely corroding and galvanically coupled condition. Additionally, the susceptibility of the titanium and nickel alloys to the formation of hydrides and resultant effects on mechanical properties as result of exposure to the descaling agents were studied at ambient and elevated temperatures.
Navy submarine and surface ships experience scaling/macro-fouling of seawater cooling system components based on homeport location and operational areas. This leads to significant system downtime and manpower expenditure by Ship Intermediate Maintenance Activities (SIMA) or Naval Shipyards for subsequent system cleanings. Currently, approved Navy cleaning methods such as hydrolancing and hot acid cleaning have significant use drawbacks.
In efforts to reduce the cost and effort associated with these cleanings, the Navy has identified a commercial water scale solvent product, namely hydrochloric acid-based descaling agent for removing seawater system scale. Others, such as phosphoric acid-based descaling agent have shown their use to be very effective for scale removal, and consequently the Uniform Industrial Process Instruction (UIPI) 5050-903 has been issued for cleaning of non-nuclear surface ship cooling systems using either of these water scale solvents.
Previous and ongoing research conducted by the Naval Research Laboratory in Key West, FL (NRLKW) determined that cleaning of 70/30 Cupro-nickel with either a 50% hydrochloric acid-based descaling agent solution or a 100% phosphoric acid-based descaling agent solution does in fact remove the passive/oxide film, which naturally forms in flowing natural seawater on these alloys. However, it was also determined that the corrosion rate during cleaning of 70/30 Cupro-nickel does not result in significantly higher corrosion rates and that subsequent to cleaning, the passive/oxide film?s regrowth is not obstructed. These experiments also indicate that hydrochloric acid-based descaling agent cleanings should be followed by a minimum of 3 weeks of continuous operation under flowing natural seawater in order to return to the original passive film protectiveness.