Intake vent plenums, ducts, trunks, and combustion air intakes draw in large amounts of air to supply interior compartments and equipment. These are critically coated areas prone to rapid corrosion due the high salt and moisture content of sea air and their exposure to the weather.
Typical Coatings Used
Intake vent plenums, ducts, trunks, and combustion air intakes must be protected by durable coatings. These areas are first coated with an anti-corrosive primer and then a protective topcoat. The new coatings of choice for extended service life are solvent-free edge-retentive systems.
If using a primer and topcoat coating method, NAVSEA Standard Item (NSI) 009-32 specifies that the primer be an anticorrosive coating qualified to MIL-PRF-23236, Coating Systems for Ship Structures. This primer must be a Type VII, and may be of a Class 5, 15B, or 17 for vent plenums, or a Class 7, 15B, or 17 for combustion air intakes.
As an alternative to the primer and topcoat coating method, NSI 009-32 recommends a single coat system using MIL-PRF-23236 Type VII, Class 5/18 or 17/18 for vent plenums and Class 17/18 paint for combustion air intakes.
To ensure proper coating adhesion, special attention should be paid to the surface preparation of intake vent plenums, trunks, ducting, and combustion air intakes. For intake vent plenums, trunks, ducting, and combustion air intakes, NSI 009-32 requires a surface that meets one of the following cleanliness standards: SSPC-SP 10/NACE 2, Near-White Metal Blast standard or SSPC-SP WJ-2/NACE WJ-2, Very Thorough Waterjetting. For combustion air intakes, surfaces may alternatively be prepared in accordance with SSPC-SP 11, Power Tool Clean to Bare Metal.
NSI 009-32 is the governing document for preservation requirements. Permitted coatings are specified in Table 3.
Ship’s Force Repairs
Ship’s force personnel are primarily responsible for maintaining coating system integrity in intake vent plenums, ducts and trunks. Naval Ships’ Technical Manuals are the primary source of information for ship’s force personnel. The applicable Chapter for surface ship preservation is Naval Ships Technical Manual (NSTM) Chapter 631, Revision 3, Preservation of Ships in Service – General.
Ship’s force personnel do very little repair work on combustion air intakes. If warranted, repair and represervation are conducted by repair activities.
New Construction Ships
New construction ships are painted in accordance with the ship build specification for that class of ship.