Limitations on Applications of Penetrant Inspection

Advantages and Capabilities of Liquid Penetrant Inspection

TM-1-1500-335-23 Nondestructive Inspection Methods Manual
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T.O. 33B-1-1 2-6 Some penetrant materials contain volatile solvents that can be nauseating. This is especially true of the vehicles in aerosol or pressure spray cans. Recommendations of the Base Bioenvironmental Engineer and the manufacturer regarding necessary personnel protective equipment SHALL be followed when using such materials. Always use adequate ventilation, as determined by the Base Bioenvironmental Engineer, to remove noticeable vapor concentrations in confined areas. CAUTION Many penetrant materials are combustible, but most have relatively high flash points. They are not considered a serious fire hazard in open tanks. However, when sprayed as a fine mist, they are easy to ignite and open ignition sources must be avoided when spraying is used. NOTE Although advantages/disadvantages may appear straightforward, the decision to select the penetrant test method or any other NDI method is often not straightforward and depends upon a large number of factors. A thorough knowledge of the capabilities and limitations of all nondestructive inspection methods is required. Whenever possible, the decision on which method to use should be referred to the cognizant NDI engineering activity. a. Penetrant inspection depends upon the ability of the penetrating media to enter and fill discontinuities. Penetrant inspection will only reveal discontinuities that are open to the surface. b. The surfaces of objects to be inspected must be clean and free of organic or inorganic contaminants that will prevent the action of the penetrating media. It is also essential that the inside surface of the discontinuities be free of materials such as corrosion, combustion products, or other contaminant that would restrict the entry of penetrant. c. Penetrants are usually oily materials with strong solvent powers and highly concentrated dyes. They will attack some non-metallic materials such as rubber and plastics. There is also the possibility of permanent staining of porous or coated materials. d. Some penetrant materials may contain either or both sulfur and halogen compounds (chlorides, fluorides, bromides, and iodides). These compounds can cause embrittlement or cracking of austenitic stainless steels if not completely removed prior to heat treating or other high temperature exposure. Entrapped halogen compounds may also cause corrosion of titanium alloys if not completely removed after the inspection is completed and the part is subjected to elevated temperatures. e. Most penetrant materials are oily in nature. Therefore, they must not be used on parts such as assemblies where they cannot be completely removed and will subsequently come in contact with gaseous or liquid oxygen. Oils, even residual quantities, tend to explode or burn very rapidly in the presence of oxygen. There are special oxygen compatible materials that SHALL be used if penetrant inspection is required and complete removal of the residue is not possible. 2.1.11 Limitations on Applications of Penetrant Inspection. 2.1.11.1 Flaw Location. Penetrant inspection is applicable to all solid, nonporous materials. The discontinuities must be open to the surface of the part. If subsurface discontinuities must be detected, another inspection method must be used.

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