Restricted Flaw Openings.
The penetrant inspection process depends upon the ability of the penetrant to enter and exit the f law
opening. Any factor that interferes with the entry or exit reduces the effectiveness of the inspection. Organic
surface coatings, such as paint, oil, grease, or resin, are in this category. Any coating that covers or blocks the
discontinuity opening will prevent penetrant entry. Even when the coating does not cover the opening, the
material at the edge of the opening may affect the entry or exit of the penetrant and greatly reduce the
reliability of the inspection. Coatings at the edge of a discontinuity will also retain penetrant, causing
background indications. An inspection method other than penetrant SHALL be used if the organic coating
cannot be stripped or removed from the surface to be inspected.
NAVY REQUIREMENT: PMB shall not precede liquid penetrant inspection
unless effective chemical etching is performed or unless specifically author-
ized without etching.
Mechanical operations, such as shot peening, plastic media blasting (PMB), machine honing, abrasive
blasting, buffing, brushing, grinding and sanding may smear or peen the surface of metals. This mechanical
working closes or reduces the surface opening of any existing discontinuities. Mechanical working (smearing
or peening) also occurs during service when parts contact or rub together. Penetrant inspection may not
reliably detect discontinuities when it is performed after a mechanical operation or service use that smears or
peens the surface.
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 and
becomes trapped. This can result in background f luorescence or color that would reduce contrast or mask
any potential discontinuity indications. In addition, removal of the penetrant may not be possible after the
BASIC PENETRANT PROCESS
BASIC PENETRANT PROCESS.
Removal, developers, process sensitivity, and general process steps are discussed. The advantages
and disadvantages of the various penetrant processes are discussed. The various specifications and
classifications which control the application of the penetrant process are also reviewed.
The information in this section is a brief non-technical description of penetrant and general process
steps. It is intended as introductory material for management, supervisors, and other personnel who
are required to know the general applications and classifications of penetrants but do not require
detailed 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 subsequent
Types of Penetrant.
The penetrant inspection process detects discontinuities open to the inspection surface by trapping a very
small amount of the penetrant. If a discontinuity is to be detected, the very small amount of penetrant must