Tanks, voids, and chain lockers are exposed to severe corrosive environments and thus require durable anti-corrosive coating systems. If these areas are not properly coated, significant corrosion issues could occur which may impact a ship’s mission capabilities.
There are many different types of tanks onboard Navy ships and each type serves a different purpose. Ballast tanks are used for both ship stability and trim considerations. Peak tanks are located at the stem and stern of a ship and may be used for ballast. Potable water tanks hold the drinking water used by Ship’s Force. Fuel-related tanks include JP-5 tanks, mobility gasoline (MOGAS) tanks, contaminated fuel tanks, DDG 51 class fuel service tanks, fuel storage tanks, compensating tanks, and bilge and oily waste tanks. Collection, holding, and transfer (CHT), marine sanitation device (MSD), and laundry drain collection tanks are used for containment of sewage treatment system waste. Feedwater and fresh water collection drain tanks are used to store pure water used in propulsion systems and waste heat boilers.
As the name implies, chain lockers house the ship’s anchor chains. Floodable voids are areas that are empty under normal conditions, but can be flooded for damage control purposes or piped for small amounts of drainage. Non-floodable voids are dry compartments that are not piped for flooding and may be designed to provide physical separation between two different types of tanks.
Typical Coatings Used
The coating system used in all tanks discussed in this page must be qualified to either MIL-PRF-23236, Coating Systems for Ship Structures or MIL-DTL-24441, Paint, Epoxy-Polyamide, General Specification for. Both specifications are available for download from the ASSIST Quick Search website. These coating systems are classified by the VOC content and other paint components, by the type of tank to which the coating will be applied, and by the substrate’s surface condition.
According to NAVSEA Standard Item (NSI) 009-32, only MIL-DTL-24441 coating systems are authorized in an aircraft carrier’s reserve feedwater and fresh water drain collecting tanks.
NSI 009-32 permits the use of MIL-PRF-23236 or MIL-DTL-24441 coating systems in aircraft carrier potable water tanks, and non-aircraft carrier reserve feedwater tanks and freshwater drain collecting tanks. All other tanks and voids will receive a MIL-PRF-23236 qualified paint system.
As an alternative to the traditional primer-stripe coat-topcoat coating system, NSI 009-32 also authorizes a single-coat coating system for certain tanks.
In ballast tanks and floodable voids, NSI 009-32 requires a single-coat MIL-PRF-23236 coating system to achieve an edge-retentive service life of either 10 to 12 years or 15 to 20 years. However, the single-coat system is not authorized for the edge-retentive service life of 5 to 7 years. Chain lockers and non-floodable voids require a single-coat MIL-PRF-23236 coating system.
To ensure proper coating adhesion, special attention should be paid to the surface preparation of tanks, voids, and chain lockers. NSI 009-32 requires a surface that meets the SSPC-SP 10/NACE 2, Near-White Metal Blast cleanliness standard.
All coating system repair work must be accomplished in accordance with NSI 009-32. All tanks, floodable voids, and non-floodable voids located at or below the waterline are designated as critical coated areas. Sumps, covers, and bolting rings associated with these areas are also included in this designation. Critical coated areas invoke a higher level of preservation process oversight and quality assurance (QA) requirements to ensure the applied coating system will achieve its maximum service life. Only those coatings specified in Table 4 of NSI 009-32 are permitted.
Ship’s Force Repairs
Ship’s Force generally do not conduct coating repairs in these spaces. The applicable Chapter for surface ship preservation is Naval Ships’ Technical Manual (NSTM) Chapter 631 (NSTM 631), Preservation of Ships in Service – General.
New Construction Installation
New construction ships are painted in accordance with the ship build specification for that class of ship.