T.O. 33B-1-1
1-20
SECTION V
PT PROCESS CONTROL
1.5
PENETRANT PROCESS CONTROL.
This section provides basic, operating and advanced level information on the procedures necessary to assure a high
quality performance from the penetrant inspection system. The first part of the section discusses the reasons for process
and materials control. The second part describes procedures to verify materials quality. The third part outlines review
functions of the process.
1.5.1
Need For Process Quality.
NOTE
Materials and process deficiencies are not always obvious. It is not easily
determined that a penetrant has lost its ability to penetrate into a given flaw. Thus,
it is necessary to periodically test the materials and to inspect the equipment and
process to be sure they are functioning.
Penetrant inspection, as well as all other nondestructive inspection processes, is not a perfect process. The presence of
indications confirms the existence of discontinuities in the part. However, the absence of indications does not
guarantee the absence of discontinuities. Flaws can be present and not be indicated for a number of reasons. The two
main reasons for discrepancies in inspection results are:
a. Substandard inspection materials due to either receipt of bad material from the manufacturer or
degradation in storage or service.
b. Process deviations either in equipment, procedures, or conditions.
1.5.1.1
New Materials.
Penetrant materials are subjected to extensive testing during their formulation to assure their proper composition.
However, materials that do not perform satisfactorily can still be received. Many times, the discrepancies in
performance have not been detected until a number of parts have been processed. Considerable effort must then be
expended to locate and reinspect the suspect parts. Unsatisfactory materials can result from a number of causes. The
penetrant supplier may inadvertently omit an ingredient or a process. An ingredient with similar characteristics may be
substituted if the original material is unavailable. The substitution of ingredients may occur at the penetrant
formulator’s supplier. Experience has shown that all newly received penetrant materials must be tested to verify
performance characteristics.
1.5.1.2
In-Use Materials.
Some inspection processes use the penetrant materials one time with no attempt to recover the excess. The materials
are usually applied by spraying, and only enough material is applied to perform the test. The materials are stored in
closed containers until they are used. These processes minimize the possibility of material contamination or
degradation during use. More often, however, the materials are used in open tanks or open containers. When the
immersion method is used, the surplus materials are allowed to drain from the part back into the tank. When the
materials are applied by brushing, the brush is alternately stroking the part surface and being immersed in the
container. Both methods provide numerous opportunities for contamination and deterioration. Materials handled in
this manner must be checked periodically to be sure they are functioning acceptably.
