TO 1-1-700 - Robins Air Force Base
TO 1-1-700 - Robins Air Force Base
TO 1-1-700 - Robins Air Force Base
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<strong>TO</strong> 1-1-<strong>700</strong><br />
9.2.4.1.1 Restricted Flaw Openings. The penetrate<br />
inspection process depends upon the ability of the penetrant to<br />
enter and exit the flaw opening. Any factor that interferes with<br />
the entry or exit reduces its effectiveness. Organic coatings,<br />
such as paint, oil, grease, and resin, are examples of this interference.<br />
Any coating that covers or bridges the flaw opening<br />
prevents penetrant entry, and even if it does not cover the<br />
opening, material at the edge of the opening affects the mechanism<br />
of penetrant entry and exit and greatly reduces the reliability<br />
of the inspection. Coatings at the edge of the flaw may<br />
also retain penetrant causing background fluorescence. An<br />
inspection method other than penetrant must be used if the<br />
organic coating cannot be stripped or removed from the surface<br />
in the area to be inspected.<br />
9.2.4.1.2 Smeared Metal. Mechanical operations, such as<br />
abrasive blasting, buffing, wire brushing, grinding, or sanding,<br />
can smear or peen the surface of metals. This mechanical<br />
working closes or reduces the surface opening of any existing<br />
discontinuities or flaws. Mechanical working (smearing or<br />
peening) also occurs during service when parts contact or rub<br />
against each other. Penetrant inspection will not reliably indicate<br />
discontinuities or flaws when it is performed after a<br />
mechanical operation or service that smears or peens the surface.<br />
Chemical etching per procedures in <strong>TO</strong> 33B-1-1 and/or<br />
system specific equipment manual is recommended prior to<br />
penetrant operations to improve test sensitivity when smeared<br />
metal is present.<br />
9.2.4.1.3 Porous Surfaces. Penetrate inspection is impractical<br />
on porous materials with interconnected subsurface<br />
porosity. The penetrant rapidly enters the pores and migrates<br />
through the network. This results in an overall fluorescence or<br />
color that masks any potential discontinuity or flaw indications.<br />
In addition, removal of the penetrant after the inspection<br />
may be impossible. If it is necessary to use an eddy current or<br />
an ultrasonic inspection for an unusual requirement, see <strong>TO</strong> 1-<br />
1-691, Chapter 4.<br />
9.2.5 Coin Tap-Test (Non-Destructive Inspection<br />
Method). The coin tap-test method is a non-destructive<br />
inspection method used to determine delaminations of the<br />
inside surfaces of tactical shelter panels (foam-beam and honeycomb)<br />
along and between the structural members. A tap<br />
hammer (see Chapter 2 of <strong>TO</strong> 35E4-1-162) shall be used in<br />
the inspection. The inspector shall be an experienced tapper.<br />
The tapping procedure consists of tapping lightly over the surface<br />
of the shelter wall. A hollow sound indicates a proper<br />
bond and a dull-thudding sound indicates areas of moisture or<br />
delamination. All shelters shall be non-destructively inspected<br />
on the inside of the shelter panels for corrosion. See <strong>TO</strong> 35E4-<br />
1-162 for field level and depot instructions of the coin-tap<br />
inspection method.<br />
9.3 EVALUATION OF CORROSION DAMAGE.<br />
Visually determine if the corrosion is present in an area which<br />
has previously been reworked. If the corrosion damage is in a<br />
previously reworked area, measure the damage to include the<br />
material which has previously been removed. A straight edge<br />
and a 10X magnifying glass may be used to assist in determining<br />
if an area has previously been reworked. Place the straight<br />
edge across the area being examined at various angles and<br />
check for irregularities, low spots, or depressions (see Figure<br />
4-5 in Chapter 4 of <strong>TO</strong> 1-1-691). If any irregularities, low<br />
spots, or depressions are found, and a visual determination<br />
cannot verify previous rework, closely examine the suspected<br />
area and the surrounding area using the 10X magnifying glass.<br />
After determining that the area has been previously reworked,<br />
evaluate the depth of the previous rework (grind-out) to determine<br />
if further metal removal will exceed grind-out limits,<br />
affect structure integrity, and require replacement of the structure.<br />
Depth measurements can also be made using the depth<br />
gages as described in Chapter 4 of <strong>TO</strong> 1-1-691.<br />
9.4 DEGREES OF CORROSION.<br />
Corrosion must be evaluated after the initial inspection and<br />
cleaning to determine the nature and extent of repair or rework<br />
needed. It is difficult to draw a distinct and specific dividing<br />
line among the degrees of corrosion, so reliable evaluation<br />
requires sound maintenance judgment. Use the following categories<br />
in reporting degrees of corrosion:<br />
9.4.1 Light Corrosion. This degree of corrosion is indicated<br />
by the protective coating being scrapped, gouged, or chipped<br />
to bare metal or showing the tracks of filiform corrosion in the<br />
film and the bare metal showing is characterized by discoloration<br />
of surface corrosion and/or pitting to a depth of approximately<br />
one mil (0.001 inch) maximum. This type of damage<br />
can normally be removed by light hand sanding.<br />
9.4.2 Moderate Corrosion. This degree of corrosion looks<br />
somewhat like light corrosion except some blisters or evidence<br />
of scaling and flaking of the coating or paint system is present,<br />
and the pitting depths may be as deep as 10 mils (0.010 inch).<br />
This type of damage is normally removed by extensive hand<br />
sanding or light mechanical sanding.<br />
9.4.3 Severe Corrosion. The general appearance of this<br />
degree of corrosion is similar to moderate corrosion in the<br />
appearance of the coating system but with severe intergranular<br />
corrosion cracks and blistering exfoliation with scaling or<br />
flaking of the metal surface. The pitting depths are deeper than<br />
10 mils (0.010 inch). This damage must be removed by extensive<br />
mechanical sanding or grinding and may require a patch<br />
type repair or component replacement.<br />
9-3/(9-4 blank)