T.O. 33B-1-12.1.11.2RestrictedFlawOpenings.The penetrant inspection process depends upon the ability of the penetrant to enter and exit the f lawopening. Any factor that interferes with the entry or exit reduces the effectiveness of the inspection. Organicsurface coatings, such as paint, oil, grease, or resin, are in this category. Any coating that covers or blocks thediscontinuity opening will prevent penetrant entry. Even when the coating does not cover the opening, thematerial at the edge of the opening may affect the entry or exit of the penetrant and greatly reduce thereliability of the inspection. Coatings at the edge of a discontinuity will also retain penetrant, causingbackground indications. An inspection method other than penetrant SHALL be used if the organic coatingcannot be stripped or removed from the surface to be inspected.2.1.11.3SmearedMetal.NOTENAVY REQUIREMENT: PMB shall not precede liquid penetrant inspectionunless effective chemical etching is performed or unless specifically author-ized without etching.Mechanical operations, such as shot peening, plastic media blasting (PMB), machine honing, abrasiveblasting, buffing, brushing, grinding and sanding may smear or peen the surface of metals. This mechanicalworking closes or reduces the surface opening of any existing discontinuities. Mechanical working (smearingor peening) also occurs during service when parts contact or rub together. Penetrant inspection may notreliably detect discontinuities when it is performed after a mechanical operation or service use that smears orpeens the surface.2.1.11.4PorousSurfaces.Penetrant inspection is impractical on porous materials, such as some types of anodized aluminum surfaces,and other protective coatings on other metals. The penetrant rapidly enters the pores of the material andbecomes trapped. This can result in background f luorescence or color that would reduce contrast or maskany potential discontinuity indications. In addition, removal of the penetrant may not be possible after theinspection.SECTION IIBASIC PENETRANT PROCESS2.2BASICPENETRANTPROCESS.2.2.1Summary.a.Removal, developers, process sensitivity, and general process steps are discussed. The advantagesand disadvantages of the various penetrant processes are discussed. The various specifications andclassifications which control the application of the penetrant process are also reviewed.b.The information in this section is a brief non-technical description of penetrant and general processsteps. It is intended as introductory material for management, supervisors, and other personnel whoare required to know the general applications and classifications of penetrants but do not requiredetailed NDI information. It can also be used in the training of beginning NDI personnel. Detailed,technical information on penetrant materials and application processes is provided in subsequentsections.2.2.2TypesofPenetrant.2.2.2.1General.The penetrant inspection process detects discontinuities open to the inspection surface by trapping a verysmall amount of the penetrant. If a discontinuity is to be detected, the very small amount of penetrant mustChange 22-7
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