Evaluation of Cleanable Shipboard Topside Coatings

ABSTRACT   Overboard discharges and other sources of running rust leave long, unsightly rust streaks down the sides of ships and these streaks are often painted over with virtually no surface preparation.  It has been estimated that Fleet-wide the Navy spends 306,000 man-days per year to paint over running rust.  The feasibility and benefit of applying cleanable coatings that would eliminate or mitigate this problem was investigated.  Three new liquid anti-graffiti based coating systems, one thermal spray thermoplastic powder coating, two pressure sensitive polyurethane based tapes, MIL-PRF-24635 haze gray topside (as the control) and the MIL-PRF-24635 with an addition of a chelating agent were selected as test candidates.  These coatings were applied on steel panels over MIL-PRF-23236 epoxy primer.  A small raw steel coupon was adhesively attached to the panels to provide a source of running rust.  The panels were placed in an accelerated corrosion cabinet and exposed to the GM 9540 test protocol for a period up to four (4) weeks (672 hours).  Every week, three panels of each coating system were removed and hand cleaned with simple vertical rubdown motions with a paper towel (dry and water wet).  The wet and dry rubdown cleaning results indicated that the polyurethane based coating systems and tape systems showed the best ease of cleaning.  Cleanability of the coatings tested in this investigation was not directly proportional to the initial gloss of the coating system.