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TO 35-1-3 - Robins Air Force Base

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CHAPTER 6<br />

CORROSION PREVENTION AND CONTROL OF NOISE SUPPRESSOR<br />

SYSTEMS (NSS)<br />

<strong>TO</strong> <strong>35</strong>-1-3<br />

6.1 GENERAL.<br />

NSS are divided into the Cold Section (temperatures of less<br />

than 300 °F) and the Hot Section (temperatures of 300 °F or<br />

more). Table 5-1 will identify the coating for a particular section<br />

based on the material and temperature. Earlier NSS were<br />

coated with alkyd enamels (TT-E-489, TT-E-527) and high<br />

temperature aluminum paint (TT-P-28) both of which are ineffective<br />

for corrosion prevention.<br />

6.2 MATERIALS.<br />

There are three basic materials used in the construction of<br />

NSS. The primary material being carbon steel this is<br />

extremely susceptible to the corrosive environment generated<br />

by the suppressor. The second material used is galvanized<br />

steel and the galvanizing will offer improved corrosion protection<br />

over the plain carbon steel, but can be used only in the<br />

Cold Section due to temperature limitations of the galvanizing.<br />

The third material used is AISI 409 stainless steel and the<br />

material has been specified in numerous rework contracts for<br />

use in the Hot Section. AISI 409 is the least expensive of all<br />

stainless steel, is weldable and will offer adequate corrosion<br />

protection.<br />

6.3 FASTENER REPLACEMENT.<br />

Any fastener replacement should be accomplished using either<br />

stainless steel fasteners or hot dip galvanized fasteners per<br />

ASTM A394, A325, or A153 (as applicable).<br />

6.4 STRUCTURAL REPAIR.<br />

6.4.1 Structural Repair Carbon Steel.<br />

6.4.1.1 If an entire component (panel, plate, beam, support)<br />

is replaced, then every side of that component must be primed<br />

prior to installation. If any part of the installation process, such<br />

as welding, damages the paint, the exposed damaged area will<br />

be cleaned and repainted after installation.<br />

6.4.2 Galvanized Steel. The amount of corrosion present<br />

will determine what is required for repair. If the corrosion is<br />

minor, then grind the corrosion and recoat with the pretreatment<br />

MIL-P-15238, and epoxy primer, MIL-PRF-23377, or<br />

MIL-DTL-53022, Type II. If the corrosion is severe or widespread,<br />

abrasive blasting may be required. When galvanized<br />

steel has been sandblasted, the primer will be organic zincrich.<br />

6.4.2.1 If an entire galvanized steel component is replaced,<br />

then every side of that component must be primed prior to<br />

installation. If any part of the installation process, such as<br />

welding, damages the paint, the exposed damaged area will be<br />

cleaned and repainted after installation.<br />

6.4.2.2 Any replacement galvanized sheet should be hot dip<br />

galvanized per ASTM A525, coating G-210. All structural<br />

steel in the galvanized condition should be hot dip galvanized<br />

per ASTM A123.<br />

6.4.3 AISI 409 Stainless Steel. Characteristics of AISI 409<br />

Steel are as follows:<br />

6.4.3.1 AISI 409 Stainless Steel is the lowest cost of all<br />

stainless steels yet it has good resistance to oxidation and corrosion.<br />

Because of a small amount of titanium, the AISI 409<br />

does not harden during welding and; therefore, does not<br />

require a post weld relief. Normally the steel has a shiny surface<br />

with areas of dull gray streaks. The streaking is caused by<br />

the titanium content and is not harmful.<br />

6.4.3.2 The AISI 409 has the following weld properties:<br />

• Failure to prime faying (back to back) surfaces of<br />

carbon steel will result in corrosion that cannot be<br />

treated without disassembly.<br />

All carbon steel items require sandblasting prior to application<br />

of the respective zinc-rich paints. The sandblasting and subsequent<br />

painting of an assembled structure will provide protection<br />

to the exposed portion of the structure, but if there is<br />

corrosion in a seam or joint, then disassembly would be<br />

required.<br />

• Gas Metal-Arc (MIG). The electrode wire should<br />

be Type AISI 409 to mild steel. When welding<br />

AISI 409 to itself, use Type 309 stainless steel<br />

when welding W 414 T filler.<br />

• Shielded Metal-Arc (covered electrodes). Use W<br />

17-4 PH, 12 Cr-4 MO or Type 330-04 electrodes.<br />

Change 8 6-1

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