(j)
Determine depth of faired depressions per par. 7.D., to ensure that
rework limits have not been exceeded.

(k)
Treat surface of reworked area per 20-50-00 immediately upon finish
of rework.

(2)Inhibited Phosphoric Acid Base Acid Rust Remover -Immersion Method

NOTE: This method is to be used for removing heavy rust from parts removed
from the airplane and where the corroded area can be completely
immersed.

(a)
Positively identify the metal as steel.

(b)
If grease or soil is present, clean the corrosion area per par. 5.

(c)
Remove heavy rust by chipping an/or wire brushing with stainless
steel wire brush.

(d)
Prepare the acid mixture per step (1)(e).

(e)
Immerse the parts in acid solution only long enough to loosen the

rust. The solution may be heated to a maximum of 104°F to increase
the removal rate. Agitation will also help.

(f)
Rinse in continuously flowing cold water rinse tank or flood with
clean water.

(g)
Visually examine the corrosion area with 10-power magnifying glass.

(h)
If corrosion still exists, repeat immersion steps.

(i)
After removal is complete, fair or blend the reworked area per par.

7.C.

(j)
Determine depth of faired depression per par. 7.D., to ensure that
rework depth limits have not been exceeded.

1) Treat surface of reworked area per 20-50-00 immediately upon fin-ish of rework.

Volume 1

20-40-00
Page 17 OCT 01/01
(3)Alkali Type Rust Remover

WARNING: THE ALKALI RUST REMOVER, SODIUM HYDROXIDE BASE, IS HIGHLY ALKALINE
AND, THEREFORE, HARMFUL TO SKIN AND EYES. PERSONNEL SHOULD WEAR
RUBBER GLOVES, APRONS AND GOGGLES WHEN WORKING WITH THIS MATERIAL.
USE WITH ADEQUATE VENTILATION.

(a)
Positively identify the metal as steel.

(b)
Protect adjacent components to prevent damage from the chemical
agents, chips, scales, or corrosion products.

(c)
Remove grease and soil from corrosion damage area per par. 5.

(d)
Remove heavy rust by chipping and/or wire brushing with stainless
steel bristle brush.

(e)
Prepare alkali base rust remover solution per manufacturer's
instruction. Carbon steel or corrosion resistant steel tanks may be
used.

(f)
Immerse parts in rust remover solution. Temperature up to the boil-ing point of the solution may be used to increase the rate of
removal.

(g)
Rinse thoroughly in clean water.

(h)
Visually examine for complete corrosion removal with a 10-power mag-nifying glass.