FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 5. Nondestructive Inspection (NDI) | 5. Penetrant Inspection | 5-62. Basic Steps to Perform Penetration Inspection
9/8/98
SECTION 5. PENETRANT INSPECTION
AC 43.13-1B
5-60. GENERAL. Penetrant inspection is
used on nonporous metal and nonmetal com-
ponents to find material discontinuities that are
open to the surface and may not be evident to
normal visual inspection. The part must be
clean before performing a penetrant inspection.
The basic purpose of penetrant inspection is to
increase the visible contrast between a discon-
tinuity and its background. This is accom-
plished by applying a liquid of high penetrat-
ing power that enters the surface opening of a
discontinuity. Excess penetrant is removed
and a developer material is then applied that
draws the liquid from the suspected defect to
reveal the discontinuity. The visual evidence
of the suspected defect can then be seen either
by a color contrast in normal visible white
light or by fluorescence under black ultraviolet
light. (See figure 5-13.)
a. The penetrant method does not de-
pend upon ferro-magnetism like magnetic par-
ticle inspection, and the arrangement of the
discontinuities is not a factor. The penetrant
method is effective for detecting surface de-
fects in nonmagnetic metals and in a variety of
nonmetallic materials. Penetrant inspection is
also used to inspect items made from ferro-
magnetic steels and its sensitivity is generally
greater than that of magnetic particle inspec-
tion. Penetrant inspection is superior to visual
inspection but not as sensitive as other ad-
vanced forms of tests for detection of
in-service surface cracks.
b. The major limitations of the penetrant
inspection is that it can detect only those dis-
continuities that are open to the surface; some
other method must be used for detecting sub-
surface defects. Surface roughness or porosity
can limit the use of liquid penetrants. Such
surfaces can produce excessive background
indications and interfere with the inspection.
Penetrant inspection can be used on most air-
frame parts and assemblies accessible to its
application. The basic steps to perform pene-
trant inspections are briefly described in the
following paragraphs.
5-61. EQUIPMENT USED IN THE
PENETRANT INSPECTION PROCESS.
Equipment varies from simple aerosol cans
used in portable systems to fully automated
computer-controlled systems. Whether fluo-
rescent or visible penetrants are used, different
penetrant bases are available but may require
different cleaning methods. Water-washable
penetrants can often be removed by a simple
water washing process, whereas oil-base
penetrants may require special solvents for re-
moval. Some oil-base penetrants have emulsi-
fiers, either added to the penetrant before it is
applied or added afterwards, that allow water
washing to be used. Developers used, can be
applied either by a wet or dry bath. Therefore,
each penetrant inspection process may require
different cleaning facilities and procedures.
(See table 5-3.)
5-62. BASIC STEPS TO PERFORM
PENETRATION INSPECTION. Table 5-4
shows a general process, in the procedures
flow sheet, for commonly used penetrant in-
spection processes. It is important to ensure
that parts are thoroughly cleaned and dried be-
fore doing penetrant inspection. All surfaces
to be inspected should be free of contaminants,
paint, and other coatings that could prevent
penetrant from entering discontinuities. Ta-
ble 5-5 shows applications of various methods
of precleaning for penetrant inspection.
Par 5-60
Page 5-29