UFC 3-460-03
21 JANUARY 2003
7.3.1.3. Seals on aboveground open-top floating-roof tanks are subject to deterioration by
atmospheric conditions. The following maintenance services are recommended and are performed
at intervals as outlined in paragraph 10.6.2:
7.3.1.3.1. Brush the fabric clamps and bolts with a nonferrous wire brush to remove rust and
scale.
7.3.1.3.2. Replace deteriorated or defective bolts; tighten loose bolts and clamps.
7.3.1.3.3. Thoroughly clean fabric surfaces with cleansing solvent.
7.3.1.3.4. Apply one or more coats of a white elastomeric coating, compatible with neoprene,
to the fabric, clamps, and bolts.
7.3.2. Belowground Tank Maintenance.
7.3.2.1. Inspection is limited to those portions of tank and lines that are exposed inside manhole
vaults and pits. Inspect these exposed surfaces periodically for corrosion and chips; repaint if
necessary.
7.3.2.2. Interior surface maintenance (including inspection for sludge deposits and corrosion)
must be on a scheduled recurring basis according to requirements in paragraph 10.6. In cleaning
interior surfaces, follow the procedure given in Chapter 11.
7.3.2.3. Operating storage tanks with below-grade access ways must have one manhole enlarged
to 0.91 meter (36 inches) in diameter and extended at least 203 millimeters above grade. Include
ladder rungs at the access way that extend to the floor.
7.3.2.4. For quality control reasons, the requirement for the slotted-gauge pipe in operating
storage tanks has been deleted from Air Force standard designs. The portion of the gauge pipe
inside the tank must be removed at the tank shell as soon as possible. Newer tanks may have a
slotted stainless steel stilling well for gauging and sampling wells.
7.3.2.5. Perform touch-up painting as required. Use applicable portions of Navy Guide
Specification, Section 09973. Surface preparation is the key to a good job.
7.4. Pressure Vacuum Vents.
7.4.1. Description and Use. Pressure vacuum vents (Figure 7.12) are required on all tanks (except
open-top floating-roof or floating-pan tanks) with a capacity of 7570 liters (2000 gallons) or more
that store products with a flash point below 37 C (98 F). Check local environmental requirements,
since this requirement may be extended to fuels with higher flashpoints or may require vapor
recovery/processing. These vents maintain working pressure in the tank within the safety limits of
pressure and vacuum, prevent normal breathing, and reduce loss of fuel by evaporation. When
pressure vacuum vents are used, flame arresters are not permitted. Where already installed with
pressure vacuum vents, flame arresters should be removed except at USAFE bases where it is a
NATO and host nation mandatory requirement that flame arresters be used in vent lines. These
flame arresters must be of the "nonfreeze" type. Figure 7.13 shows a simple belowground tank vent.
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