T.O. 33B-1-11-20SECTION VPT PROCESS CONTROL1.5PENETRANTPROCESSCONTROL.This section provides basic, operating and advanced level information on the procedures necessary to assure a highquality performance from the penetrant inspection system. The first part of the section discusses the reasons for processand materials control. The second part describes procedures to verify materials quality. The third part outlines reviewfunctions of the process.1.5.1NeedForProcessQuality.NOTEMaterials and process deficiencies are not always obvious. It is not easilydetermined 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 andprocess to be sure they are functioning.Penetrant inspection, as well as all other nondestructive inspection processes, is not a perfect process. The presence ofindications confirms the existence of discontinuities in the part. However, the absence of indications does notguarantee the absence of discontinuities. Flaws can be present and not be indicated for a number of reasons. The twomain reasons for discrepancies in inspection results are:a. Substandard inspection materials due to either receipt of bad material from the manufacturer ordegradation in storage or service.b. Process deviations either in equipment, procedures, or conditions.1.5.1.1NewMaterials.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 inperformance have not been detected until a number of parts have been processed. Considerable effort must then beexpended to locate and reinspect the suspect parts. Unsatisfactory materials can result from a number of causes. Thepenetrant supplier may inadvertently omit an ingredient or a process. An ingredient with similar characteristics may besubstituted if the original material is unavailable. The substitution of ingredients may occur at the penetrantformulator’s supplier. Experience has shown that all newly received penetrant materials must be tested to verifyperformance characteristics.1.5.1.2In-UseMaterials.Some inspection processes use the penetrant materials one time with no attempt to recover the excess. The materialsare usually applied by spraying, and only enough material is applied to perform the test. The materials are stored inclosed containers until they are used. These processes minimize the possibility of material contamination ordegradation during use. More often, however, the materials are used in open tanks or open containers. When theimmersion method is used, the surplus materials are allowed to drain from the part back into the tank. When thematerials are applied by brushing, the brush is alternately stroking the part surface and being immersed in thecontainer. Both methods provide numerous opportunities for contamination and deterioration. Materials handled inthis manner must be checked periodically to be sure they are functioning acceptably.
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