(5)Corrosion removal on steels heat-treated to 220,000 psi and above shall
be accomplished by dry abrasive blasting as outlined in par. 7.E., with
blasting pressure ranging from 40 to 70 psi or hand tools described in
par. 7.E.

(6)Mechanically remove all corrosion from steel parts heat-treated below
220,000 psi as follows:

(a)
Remove heavy corrosion products using stainless steel hand brush.
Use dry abrasive blasting per 7.E., as an alternate method with
blasting pressures ranging from 40 to 70 psi.

(b)
Remove residual corrosion by hand sanding or with approved hand-
operated power tool as outlined in par. 7.E. Select appropriate
abrasives from Fig. 3.

(7)Make visual check through a 10-power magnifying glass to ensure that all
corrosion is removed.

(8)Fair depressions resulting from reworked per par. 7.C., and surface fin-ish with 400 grit abrasive paper selected from Fig. 3.

(9)Clean reworked area.

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

(11)Treat reworked area as indicated in 20-50-00 immediately upon finish of
rework.

C. Corrosion Removal -Chemical. Chemical rust removers are of either the acid
or alkaline type. The acid type is intended for use in removing the rust or
black oxide formations by either immersion or brush application of the chem-ical. The alkaline type is intended for use in removing red rust by immer-sion treatment. Procedures for the use of both types of rust removers are
provided below.

CAUTION: STEEL PARTS HEAT-TREATED ABOVE 220,000 PSI ARE SUBJECT TO HYDROGEN
EMBRITTLEMENT, AND THE USE OF ACID IS PROHIBITED.

(1)Inhibited Phosphoric Acid Base Rust Remover -Brush-on Method

(a)
Positively identify the metal as steel.

(b)
Protect adjacent area to prevent additional damage from the chemical
agents.

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

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

Volume 1

20-40-00

Page 16
OCT 01/01

(e)
Dilute the concentrated acid according to manufacturer's instruc-tions in acid resistant mixing container. Do not add water to acid;
always add acid to water.

(f)
Apply the acid mixture to corroded area with acid-resistant brush.
Allow to remain long enough to loosen rust (2 to 10 minutes) and
rinse completely with clean water.

(g)
Examine corroded area visually with 10-power magnifying glass.

(h)
If corrosion is still evident, repeat application and rinse thor-oughly.

(i)
After removal is complete, blend or fair area affected per par. 7.C.
　
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