parent film characteristics will be significantly altered by the use of automatic processing. It should be noted that film
quality, when automatic processing is used, is generally slightly lower than that which is obtainable with manual
processing. However, the advantage of speed of processing, lower manpower requirements, and consistency of
development generally are felt to be more important in the decision to use automatic processing.
5-9. Radiographic Interpretation. Interpretation of radiographic images cannot be translated into mathematical
formulas or routine procedures. The wide variety of test objects and the various fabrication process by which they have
been made makes radiographic interpretation a complex subject. Interpretation of the shadow images visible in the
radiograph is an acquired skill and there is no substitute for experience. Experience aids the film reader in recognizing
discontinuities and in identifying where they can be expected to occur in a particular or structure.
Interpretation. Radiographic inspection is conducted to assure that a part has the required integrity to reliably
perform the function for which it was designed. This does not mean perfection. All parts and processes are imperfect.
Therefore, the purpose of radiography is to determine the degree of Imperfection. The effects of discontinuities or
manufacturing deviations must be correlated with the function of the part Specifications are usually used to spell out the
discontinuities that may be considered detrimental to the function of the part and the acceptable magnitudes of the
discontinuities It is the duty of the film interpreter to recognize the various discontinuities, their magnitudes, and be
capable of relating them to the particular specification required. The responsibility and capability of the radiographic
interpreter cannot be overemphasized.
Castings. Radiographic examination is ideally suited to the inspection of castings because the most
common casting discontinuities are three dimensional and are, therefore, almost independent of angle of inspection.
Exceptions in some cases include fine cracks, cold shuts, unfused chills and chaplets. To reveal these, the radiation
must be at or near the same parallel plane as the discontinuity. Hairline surface cracks, such as those produced by
grinding, are seldom, if ever, revealed by radiography
Welds Most weld discontinuities can be readily detected by radiographic Inspection since they consist of a
change in the metal homogeneity Cracks in welds are often detectable since they will usually occur in the direction of the
thickness of the plate and will be parallel to the X-ray beam. Stresses created in the metal by welding and not
accompanied by a physical separation of material will not be detected by radiography, and cracks not properly oriented
may also be missed. Oxides created by the molten metal may be trapped in the weld. This condition results in reduced
strength and is subject to review to determine possible implication as a result of the service the weld is expected to yield.
Service inspection. When parts are utilized as required in the design of modern aircraft, there is
occasional failure due to fatigue. These failures are a result of overstress of the part due to unusual operating conditions
or deterioration of the part. This type of part change is most difficult to detect due to the very nature of the changes and
the inaccessibility of the areas In which these changes are most likely to occur in an aircraft. These service type changes
in an aircraft are usually due to wear, corrosion, fractures, or shear. Radiography has been used to detect these
conditions when they occur in inaccessible areas and are not available for visual inspection
Wear. Rivets and bolts may wear the skin, spar, and frame holes so that there is not a correct fit in the
holes for adequates strength in joints or attachments of awing section. This can occur due to continued flexing of
components from use or because of severe stress due to unusual operating conditions In turbulent weather or an adverse
landing. This condition may also result in radial cracks from bolt holes. This type of failure is extremely difficult to detect
by radiography. Any angle of exposure results in superimposition of bolt or nut over crack Loose bolts and rivets have
been detected satisfactorily when occurring in position to be located Elongation of rivet holes caused by bearing failure or
sheared rivets should not be confused with elongation of holes from drilling. If fatigue is suspected In a riveted joint, the
half moon indications should all be on the same side of the rivet and the rivets in the joint should show similar indications
of failure. Intermittent indications would normally be considered fabrication tolerance.
Corrosion. Corrosion may occur in an aircraft part which reduces its strength and expedites the
possible failure. This deterioration of the metal may be due to electrolytic action, moisture, chemicals or gases which
attack the metals, intergranular action due to improper heat treatment at the time of manufacture, or other factors. This
condition usually occurs on internal surfaces of such components as tubular supports or housings. Since corrosion
represents a change of material and occurs in all directions, it is easily detected by a proper radiographic exposure.