TM 1-1500-204-23-7
NOTE
Personnel wearing light sensitive eye glasses are prohibited from wearing these eyeglasses
while performing fluorescent magnetic particle inspections. Light transmission losses of 16 to
45 percent have been revealed when wearing light sensitive glasses exposed to ultraviolet
light. These light transmission losses may adversely affect the ability of the inspector to detect
small indications.
3-12. Inspection and Interpretation. The following paragraphs describe inspection and interpretation of the penetrant
inspection testing.
a.
Inspection. Inspection preparation, basic inspection principles, and flaw indications are discussed in the
following paragraphs.
(1)
Inspection preparation. The inspector shall perform the following steps prior to inspection:
(a)
The inspector shall check to ensure that the area is clean and contains no items which will contaminate
the part under test, particularly in fluorescent light.
(b)
The inspector shall prepare himself to ensure hands and clothing are not contaminated with penetrant.
(c)
The intensity of illumination for the surface used for inspection shall be checked for a minimum of 90
foot-candles measured at a distance of 15 inches.
(d)
When working in a darkened area the inspector shall place himself in a darkened area, to be dark
conditioned, for at least five minutes each time the darkened area is entered from white light or the inspector looks into
the direct beam of black light.
(2)
Basic inspection principles. There are five principles which apply to all penetrant processes that each
operator should remember at all times. Each of these principles is discussed in one of the following paragraphs.
(a)
Cleaning. Cleaning the part is essential to remove contamination from out of the flaws or
discontinuities. This facilitates more effective entrance of the penetrant liquid into the flaw cavities. Surface openings
that are uncontaminated, regardless of how fine, are seldom difficult to detect with suitable penetrant inspection
processes.
(b)
Penetration. The penetrant must enter the defect in order to produce an indication. It is always
important to allow sufficient penetration time so that the penetrant can fill the defect. It is also essential that the defect
be clean and free of contaminants so that the penetrant is free to enter.
(c)
Washing. If all penetrant is washed out of a defect, an indication cannot be formed. During the
washing operation prior to developing, it is possible that the penetrant may be removed from within the defect as well as
from the surface. If this happens, less intense indications will be formed. The use of non-water-washable penetrants
should considerably increase the accuracy of penetrant inspection for shallow defects or fine cracks, since the penetrant
is not water removable. In this case, only the surface penetrant can be removed by water rinsing because the application
of emulsifier combines only the excess surface penetrant to render it water rinseable. Excess surface penetrant should
never be removed by the use of solvent wash or vapor degreasers, because these procedures are too effective and may
remove penetrant from defects to the extent that proper flaw indications cannot be obtained.
(d) Defect size. The smaller the defects, the longer the penetrating time. Fine apertures require a longer
penetrating time than larger defects, such as pores. The fact that they are smaller means that the penetrant will enter
more slowly.
(e)
Special considerations. Wide openings require special techniques. Refer to TM 55-1500-33523 for
these techniques. In general, if a surface discontinuity is wider than it is deep, the washing or rinsing operation may
remove the penetrant and produce less visible indications.
(3)
Flaw indications. There are five basic types of indications which may be seen by the inspector. Each is
explained in one of the following paragraphs.
(a)
Continuous line. A crack, a cold shut, and a forging lap usually show as continuous line indications. A
crack will appear as a sharp or faint jagged line, straight line, or intermittent line. Cold shuts will usually appear as
smooth, straight, narrow lines. Scratches and die marks will also appear as straight lines, but the bottom of the
discontinuity is usually visible.
3-11
