MIL-HDBK-1110
sheet. In some cases, a coating manufacturer may state that a
coating should only be used over a white-metal finish (SSPC
SP 5). After application of the total system, it should be
checked for holidays with a low-voltage holiday detector as
described in the National Association of Corrosion Engineers
(NACE) RPO188, Standard Recommended Practice, Discontinuity
(Holiday) Testing of Protective Coatings. Any holidays that are
located should be repaired.
Repair of damaged coatings will vary somewhat with the
existing coating system. Normally, repairs are made with the
type of coatings already on the tanks. If these are not
available, another compatible coating system must be used.
Compatibility of coatings can be determined as described in par.
5.6.2. Localized exposed steel should be spot abrasively blasted
to an SSPC SP 10 condition and the intact coating surrounding
these areas should be brush-off blasted (SSPC SP 7) to a 2-inch
width. The patch of the same or a compatible coating system
should be applied to steel and extend 2 inches onto the cleaned
intact coating.
5.3.1
Interiors of Steel Fuel Tanks. Interiors of steel
storage tanks should be cleaned as described in NFGS-13219,
Cleaning Petroleum Storage Tanks, and inspected regularly.
Because it may not be possible to do this conveniently, it is
critical that they receive long-lasting, high-performance
interior coating systems. Corrosion occurs most frequently on
the floors of the tanks, where water is always present despite
its frequent removal from sumps. Thus, the bottoms of steel tank
interiors should be measured for adequate thickness before
blasting and recoating is initiated. It may be necessary to fill
pits with weld metal, apply a false bottom of fiberglass-
reinforced plastic as described in NFGS-13217, Fiberglass-Plastic
Lining for Steel Tank Bottoms (for Petroleum), or install a new
replacement steel bottom. All steel storage tank interiors
should be given a near-white blast (SSPC SP 10) immediately prior
to priming.
For many years, fuel tank interiors have been
successfully lined with a three-coat epoxy system with a total
dry film thickness of 9 mils. Coats of epoxy-polyamide
conforming to Formulas 150, 151, and 152 of MIL-P-24441 have been
the epoxy system most frequently used to line military steel fuel
tanks. It is described in NFGS-09973, Interior Coating System
for Welded Steel Petroleum Storage Tanks.
More recently, a urethane system was developed for
lining steel fuel tanks. As described in NFGS-09970, Interior
Coatings for Welded Steel Tanks (for Petroleum Fuels), it
consists of a pretreatment wash primer, a polyurethane primer, a
polyurethane intermediate coat, and a finish coat. The finish
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