MIL-HDBK-1110
coat may be a polyurethane or a special fluorinated polyurethane.
These coatings currently exceed the VOC limit of 340 grams per
liter that exists in many locations, the fluorinated polyurethane
coating is very expensive, and the pretreatment wash primer and
the primer contain chromate. However, because of the reported
much longer life of the system with the fluorinated polyurethane
finish, it is recommended for Navy fuel tanks, wherever it is
legal to use it.
After application of each coat of interior paint, tank
interiors must be thoroughly ventilated to remove organic solvent
vapors and to assist in curing (solvent release) of coatings.
Ventilation requirements vary with tank size, shape, and number
of openings. Safety requirements and instructions of coating
manufacturers should be followed. Heated air can also be used to
accelerate curing of coatings. Blasting and painting hoses, as
well as other electrical equipment, should be grounded and
sparkproof. The local industrial hygienist can provide
information on health and safety requirements for the lining
operation. It is especially important to require holiday testing
of the interior tank coatings. In this way, small defects can be
found and repaired, preventing sites for premature initiation of
corrosion.
5.3.2
Exteriors of Steel Fuel Tanks. The exterior coating of
steel fuel tanks is described in NFGS-09971, Exterior Coating
System for Welded Steel Petroleum Storage Tanks. For new tanks,
a system that has performed well is two coats of epoxy-polyamide
(e.g., MIL-P-24441 Formulas 159 and 151) and a finish coat of
aliphatic polyurethane (e.g., MIL-C-85285) to a total dry film
thickness of at least 8 mils. The recommended surface
preparation is an SSPC SP 10 near-white blast. Refer to
par. 4.4.3 for maintenance painting of exterior tanks.
5.4
Steel Water Tanks. Newer steel water storage tanks
have welded sections. Older riveted or bolted tanks are still
used, however, at some activities. The seam areas of such tanks
are much harder to completely coat. Cathodic protection, as
described in NFGS-13112, Cathodic Protection System (Steel Water
Tanks), CEGS 16641, Cathodic Protection System (Steel Water
Tanks), and MIL-HDBK-1004/10, Electrical Engineering Cathodic
Protection, is recommended for water tank interiors to supplement
the protection afforded by coatings. Corrosion of cathodically
protected water tanks generally is usually concentrated at the
top of the tank along sharp edges, crevices, and beams supporting
the roof, where cathodic protection does not occur. Thus, it is
important to coat and inspect these areas especially well.
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