angle other than 90 degrees to the X-ray film and not parallel with the X-ray beam offers very little difference to the
radiation transmission and may not be visible in the radiographic image. Radiography can only be depended on to
reveal crack-like discontinuities that are aligned within approximately 7 degrees of the X-ray beam. This depends on
the thickness and width of the crack. Normally cracks that are easily detectable by X-ray are visible to the naked eye.
Radiography may be used to determine extent of cracks or other conditions detected visually or by magnetic particle or
penetrant methods of inspection. In castings, crack-like discontinuities can be due to shrinkage, hot tears, cold shuts,
or other sources typical of the casting process. In weldments, longitudinal or transverse cracks may be found. Lack of
weld penetration produces a crack-like discontinuity. The forging process can introduce cracks, laps, and seams that
appear crack-like in radiographic images.
Water In Honeycomb.
A typical condition that occurs in honeycomb structures is the formation of water in the cores. This entrapped water
freezes and expands at high altitudes. The expansion distorts the cells and can break the bonds between core and
facing sheets. When this condition exists, vibration of the face sheet can occur causing failure of adjacent bonds and
propagation of bond failure. Entrapped water causes corrosion of both face sheet and core material. Radiographic
inspection is conducted to evaluate core damage and water content as a maintenance inspection. Entrapped water in
honeycomb cells usually appears as a smooth, consistent, light density area that does not have a grainy or porous
appearance. The lightest area (more dense substance) indicates greater amounts of water.
a. Epoxy in honeycomb cells appears grainy, non-homogeneous. If the cell is not spotty and completely
filled, the epoxy will be located around the periphery of each cell.
b. Radiographic inspection for moisture detection can be made with the honeycomb core cell walls in
either the vertical or horizontal plane. The preferred method is with the core cell walls in the
horizontal plane because core cells which are partially filled with moisture are more readily identifiable
(less easily confused with solid adhesive).
c. If practical, confirmation of partially filled cells with water can be made by repeating the radiographic
procedure with the honeycomb cell walls in the opposite plane.
d. Radiographic exposures indicating filled core cells are not always conclusive for moisture detection and
should be confirmed by other means if possible.
Location of Foreign Objects.
Radiography is an excellent method to locate and evaluate foreign objects. Foreign objects may be free rivets, bolts, or
other objects that could be detrimental to the function of the part or assembly.
Radiography has found wide use in the revaluation of various assemblies to determine status or condition. If the use of
the assemblies produces changes in it which are recordable by an X-ray beam, then radiography may be useful in
supplying confirming evidence of the suspected condition. Radiographic inspection of oil coolers has resulted in an
inspection method that can detect foreign material in the cooler.
Radiographic inspections, after completion of repair, assure quality of workmanship. On occasion components are mis-
assembled. In some areas it is not possible to check dimension by physical or visual means. Radiography may be used
if precautions are taken to assure proper geometrical relation to determine dimension of internal spacing.
It is inherent to good practice in many cases that castings or weldments are thicker in cross section than required for
the necessary strength of the part. For this reason some flaws in the casting can be tolerated with no detrimental effect
to the aircraft. In order to determine what castings or weldments are acceptable for use in an aircraft, standards of