Radiographic Inspection
RADIOGRAPHIC INTERPRETATION.--The
usefulness of the information obtained from the
Radiographic is a nondestructive inspection
radiographic process depends upon the intelligent
method that uses a source of X-rays to detect dis-
interpretation of the derived image. To successfully
continuities in materials and assembly components.
interpret the radiograph, the radiographic interpreter
Radiation is projected through the item to be tested, and
must have a working knowledge of the component or
the results are captured on film. Radiography may be
material and be able to relate the images to the
used on metallic, nonmetallic, and combination
conditions likely to occur. Specifications are used to
metallic/nonmetallic materials and assemblies without
spell out the discontinuities that maybe considered
access to the interior. However, defects must be
detrimental to the function of the part and the
correctly aligned and oriented with respect to penetrat-
acceptable magnitudes of the discontinuities. It is the
ing rays to be reliably detected. Radiography is one of
duty of the film interpreter to recognize the various
the most expensive and least sensitive methods for
discontinuities, their magnitudes, and be capable of
crack detection. It should only be used to detect flaws
relating them to the particular specification required.
that are not accessible or favorably oriented for use by
The responsibility and capability of the radiographic
other test methods.
interpreter cannot be overemphasized. Often, many
human lives and investments of millions of dollars are
The extent of recorded information is dependent
depending on the judgment of the radiographic
upon the following three prime factors:
interpreter.
1. The composition of the material.
RADIATION HAZARD.--Radiation from X-ray
2. The product of the density and the thickness of
units is destructive to living tissue. It is universally
the material.
recognized that in the use of such equipment, adequate
protection must be provided to personnel. Personnel
3. The energy of the X-rays, which is incident
must keep outside the primary X-ray beam at all times.
upon the material. Material discontinuities cause an
apparent change in these characteristics, and thus make
Radiation produces changes in all matter that it
themselves detectable.
passes through. This is also true of living tissue. When
the radiation strikes the molecules of the body, the
Figure 6-10 is a diagram of radiographic exposure
effect may be no more than to dislodge a few electrons;
showing the elements of the system. Radiation passes
but an excess of these changes could cause irreparable
through the object and produces an invisible or latent
harm. When a complex organism is exposed to
image in the film. When processed, the film becomes a
radiation, the degree of damage, if any, depends on
radiograph or shadow picture of the object. Since more
which of its body cells have been changed. The more
radiation passes through the object where the section is
vital parts are in the center of the body; therefore, the
thin or where there is a space or void, the corresponding
more penetrating radiation is likely to be the more
area on the film is darker. The radiograph is read or
harmful in these areas. The skin usually absorbs most
interpreted by comparing it with the known nature of
of the radiation; therefore, it reacts earliest to radiation.
the object.
If the whole body is exposed to a very large dose of
radiation, it could result in death. In general, the type
and severity of the pathological effects of radiation
depend on the amount of radiation received at one time
and the percentage of the total body exposed. The
smaller doses of radiation may cause blood and
intestinal disorders in a short period of time. The more
delayed effects are leukemia and cancer. Skin damage
and loss of hair are also possible results of exposure to
radiation.
Ultrasonic Inspection
The term ultrasonic means vibrations or sound
waves whose frequencies are greater than those that
Figure 6-10.--Diagram of radiographic exposure.
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