NONDESTRUCTIVE TESTING MANUAL
PART 9 - VISUAL - GENERAL
1. GENERAL
A. Visual inspection procedures are among the simplest and most economical
of all the nondestructive testing methods.
B. Optical instruments can be used to assist the inspection by magnifying
discontinuities that are too small to be seen by the unaided eye.
C. Other instruments may also be used to inspect areas where the access is
difficult.
2. VISUAL PROCEDURES
A. When performing visual inspections it is essential to know the types of
discontinuity which may develop, and the areas where these failures might
occur.
B. A general check of the inspecion area should be made for cleanliness,
security of parts and obvious damage.
C. After completion of a general check, a specific procedure should be
followed:
- gain access to the inspection area,
- clean the surface of the inspection area whenever possible,
- provide adequate lighting for the inspection,
- carefully examine the specified area,
- record all relevant indications.
NOTE: If the geometry and location of, or access to, the inspection area
conceals the part which is to be inspected, visual aids may be
used - mirror, magnifying glass, endoscope etc.
0 Page 901
51E90 00 Feb 01/03
PRINTED DATE: Printed in Germany
NONDESTRUCTIVE TESTING MANUAL
PART 9 - VISUAL - GENERAL
VISUAL INSPECTION AIDS
A. Magnifying Devices
(1) Hand-held magnifying glasses:
- Low-power magnifiers may be used for large surface areas
(x2 - x6 magnification).
- Higher-power magnifiers may be used for more detailed inspections
of small, local areas (x8 - 0 0 magnification).
(2) Microscopes, of various magnifying powers, may be used to inspect
local areas on critical parts.
B. Rigid Endoscopes (Refer to Figure 901)
(1) An endscope is a precision optical instrument which can be used to
inspect internal areas and the inside surfaces of holes, bores and
tubes.
(2) A rigid endscope has a metal tube containing a series of lenses,
which provide a view of the inspection area, and a lighting system
which directs light to the inspection area.
(3) Rigid endoscopes are available in sizes ranging from approximately
2.0 mm (0.07 in.) in diameter and a few centimeters in length, to
approximately 19.0 mm (0.79 in.) in diameter and many centimeters
(feet) in length.
(4) Endoscopes can be supplied with optical systems which will provide
direct, right angle, rear and fore oblique directions of view.
(5) Many endoscopes have an adaptor on the eye-piece which allows
the image of the inspection area to be recorded on photographic
film, on video, or to be viewed with a Closed Circuit TV
system (CCTV).
(6) Endoscopes usually have high image resolution and a depth of field,
ranging from a few millimeters (fractions of an inch) to infinity.
(7) Rigid endoscopes are available with various magnification powers and
adjustable focus controls.
5 1 m 9 O10
Page 902
Feb 01/03
PRINTED DATE: Printed in Germany
A 3 1 81A3 1 91A3201A321
NONDESTRUCTIVE TESTING MANUAL
PART 9 - VISUAL - GENERAL
-EYE-PIECE
VIEWING LENS
EXAMPLES OF ANGLES OF VIEW
CABLE TO LIGHT SOURCE
DIRECT
Z7ZI
-RIGID TUBE
CONTAINING
INTERMEDIATE
LENS SYSTEM
AND LIGHT
GUIDE REAR OBLIQUE
WORKING
LENGTH
(mm)
RIGHT ANGLE
-LIGHT EMISSION
-OBJECT LENS FORE OBLIQUE
DIAMETER (mm)
Page 903
51-90 0( Feb 01/03
PRINTED DATE: Printed in Germany
A3181A3191A3201A321
NONDESTRUCTIVE TESTING MANUAL
PART 9 - VISUAL - GENERAL
C. Flexible Endoscopes (Refer to Figure 902)
(1) Flexible endoscopes are armored plastic tubes which can be
manipulated into various curves and angles thus permitting access to
areas which are inaccessible to rigid endoscopes. They are also
available in various diameter/Length combinations.
(2) These endoscopes do not have an intermediate lens system within the
flexible tube. At each end of the tube is a lens system connected by
two bundles of glass fibers. The outer bundle of fibers transmits
light to the inspection area whilst the inner bundle transmits the
image of the inspection area to the lens in the eyepiece. The
lighting is usually provided by an external, variable intensity, cold
light source. At the eyepiece there is a focusing ring which permits
adjustment of image clarity.
(3) Flexible endoscopes may have replacement object lenses which provide
a change of the angle, or field, of view. Some endoscopes have a
knob, near the eyepiece, which controls a steerable tip (distal
end). This control permits changes of angle of view and allows the
distal end to be steered past obstructions.
(4) The image resolution of flexible endoscopes is, generally, lower than
that of rigid endoscopes.
(5) Where access is difficult, it may be necessary to use guide tubes to
enable the endoscope to be directed to the inspection area. Details
of guide tube requirements would be stated in the specific NTM
visual procedure.
(6) Adaptors are also available to enable the image of the inspection
area to be recorded on photographic film, on video, or to be viewed
with a CCTV system.
Page 904
EFFECTIVITY: A318,A319,A320,A321 51-90-00 Feb 01/03
PRINTED DATE: Printed in Germany
A3181A3191A3201A321
NONDESTRUCTIVE TESTING MANUAL
PART 9 - VISUAL - GENERAL
DISTAL
END
DISTAL END
CONTROL KNOB
EYEPIECE
LIGHT SOURCE BOX
i
o
<
s
z
Page 905
EFFECTIVITY: A318,A319,A320,A321 51-90-00 Feb 01/03
PRINTED DATE: Printed in Germany
NONDESTRUCTIVE TESTING MANUAL
PART 9 - VISUAL - GENERAL
D. Black Light
WARNING 1: BLACK LIGHT SOURCES MUST NOT BE OPERATED IN THE PRESENCE OF
FLAMMABLE VAPOURS. THESE SOURCES HAVE OPERATING TEMPERATURES
ABOVE THE IGNITION POINT OF MOST FUEL VAPOURS.
WARNING 2: DO NOT TOUCH THE HOUSINGS, OR FILTERS, OF BLACK LIGHT
SOURCES WITH BARE SKIN WHILST SOURCES ARE ENERGIZED OR UNTIL
THEY HAVE COOLED. SEVERE BURNS MAY RESULT.
WARNING 3: DO NOT OPERATE BLACK LIGHT SOURCES WITHOUT FILTERS OR WITH
ILLFITTING, OR CRACKED FILTERS. UNFILTERED ULTRAVIOLET
RADIATIONS CAN BE HARMFUL TO THE EYES AND SKIN.
(1) That portion of the ultraviolet light spectrum which lies between
320 to 400 nanometers in wavelength is called black light.
(2) Petroleum-based products and certain other materials fluoresce under
black light so it can be used for:
(a) Magnetic particle inspection procedures.
(b) Penetrant inspection procedures.
(c) Visual detection of leaks (fuel and oil).
(d) Visual detection of contaminants (soil, solder flux, lint).
NOTE: Glassfibers absorb ultraviolet light to a significant
extent. Special light conductors (fluid conductors) must
be used when endoscopes are used in conjunction with
ultraviolet light.
(3) Althrough black light is not dangerous, certain precautions are
necessary when using the high-pressure mercury lamps which usually
provide the black light source.
(a) The filter on these lamps must always be maintained in good
condition.
(b) Do not use the lamp if the filter is cracked or missing.
(c) Do not look directly at the light source.
(d) Avoid prolonged exposure on skin tissue.
(e) Do not wear photochromatic spectacles when doing inspections
which involve the use of black light sources.
(4) The output value of black light sources must be checked at regular
intervals to ensure that it has not fallen below the approved limit.
Page 906
5190-OC Feb 01/03
PRINTED DATE: Printed in Germany
