Louvers are installed in the exterior bulkheads of intake and uptake spaces to allow for unimpeded air flow to the intake or from the uptakes while limiting the amount of rain and sea spray that can enter the intake or uptake. These exterior louvers are subjected to sea spray and ultraviolet radiation. Due to their angular geometry, surface preparation is a critical step in ensuring a long lasting and uniform protective coating.
Typical Coatings Used
Intake and uptake louvers must be protected by durable coatings. Coatings qualified to MIL-PRF-23236, Coating Systems for Ship Structures, are the coatings of choice for extended service life. Depending on the ship configuration, louvers may be coated using either an epoxy- or powder-based coating system.
Epoxy coatings for intake and uptake louvers are qualified to MIL-PRF-23236, Type VII, and may be applied as a primer and topcoat, or as a single coat. For a primer and topcoat application, both the primer and topcoat must be Class 5 or 7. For a single coat application, the coating must be Class 7/18.
Powder coatings for chevron louvers are qualified to MIL-PRF-23236, Type VIIIA, and are applied by air-injected fluidized bed method only.
To ensure proper coating adhesion, special attention should be paid to the surface preparation of the louvers. For epoxy coating systems, NSI 009-32 requires a surface that meets the cleanliness standards of either NACE 2/SSPC-SP 10, Near-White Metal Blast; or NACE/SSPC-SP WJ-2, Very Thorough Waterjetting. For powder coating systems, NSI 009-32 requires a surface that meets the cleanliness standard of NACE 2/SSPC-SP 10, Near-White Metal Blast.
NSI 009-32 is the governing document for preservation requirements. Permitted coatings are specified in Table 2 and 3. All intake and uptake louver coating system preservation efforts must be accomplished in accordance with NSI 009-32.
Ship’s Force Repairs
Ship’s force personnel may touchup louvers in accordance with Naval Ships Technical Manual: Chapter 631 (NSTM 631), Preservation of Ships in Service – General. NSTM 631 provides requirements, instructions, and guidance for surface preparation and coating application.
New Construction Installation
New construction ships are painted in accordance with the ship build specification for that class of ship.