a. In Step 1, Cleaning is a critical part of the penetrant process and is emphasized because of its effect on
the inspection results. Contaminants, soils or moisture, either inside the flaw or on the part surface at
the flaw opening, can reduce the effectiveness of the inspection.
b. In Step 2, a penetrating liquid containing dye is applied to the surface of a clean part to be inspected.
The penetrant is allowed to remain on the part surface for a period of time to allow it to enter and fill
any openings or discontinuities open to the surface.
c. After a suitable dwell period, the penetrant is removed from the part surface, in Step 3. Care must be
exercised to prevent removal of penetrant contained in discontinuities.
d. A material called a developer is then applied (Step 4). The developer aids in drawing any trapped
penetrant from discontinuities and improves the visibility of indications.
e. The final process step (Step 5) is a visual inspection under appropriate lighting conditions to identify
Penetrant is also used to detect leaks in containers. The same basic fundamentals apply but the penetrant removal step
may be omitted. The container is either filled with penetrant or the penetrant is applied to one side of the container
wall. The developer is applied to the opposite side, which is visually inspected after allowing time for the penetrant to
seep through any leak points. This method may be used on thin parts where there is access to both surfaces and the
discontinuity is expected to extend through the material.
The apparent simplicity of the penetrant inspection is deceptive. Very slight variations in performing the inspection
process can invalidate the inspection by failing to indicate serious flaws. It is essential that personnel performing
penetrant inspection be trained and experienced in the penetrant process. All individuals who apply penetrant
materials or examine components for penetrant indications shall be qualified as specified in Chapter 1, Section 1.2.
The equipment used in the penetrant inspection process varies from aerosol spray cans to complex automated systems.
Some of the more generally used types of equipment are briefly described in the following paragraphs.
Penetrant inspection can be performed on installed parts (e.g., on aircraft) or on parts too large to be brought to the
inspection area. Penetrant materials are available in aerosol spray cans and in small containers for brush or wipe
applications. Generally, portable penetrant applications are limited to localized area or spot inspections rather than
entire part surfaces.
Stationary Inspection Equipment.
The type of equipment most frequently used in fixed installations consists of a series of modular workstations. At each
station an inspector performs a specific task. The number of stations in a processing line varies with the type of
penetrant method used. Typical stations are: dip tanks for penetrant, remover or emulsifier, and developer; drain or
dwell areas; a spray wash area with a black light; a drying oven; and an inspection booth. The drain or dwell stations
are roller top benches to hold the parts during the processing cycle. The usual arrangement is to position a drain or
dwell station following each of the dip tanks, the wash station and the drying oven.
Small Parts Inspection Unit.
There are inspection units designed for processing small parts. The units are smaller than the general systems
described in paragraph 220.127.116.11, and some of the stations serve multiple purposes. In use, the parts are loaded into wire
baskets that are then batch processed through each of the stations. The wash station may contain a water-driven, rotary
table with spray jets to supplement the hand held spray wand. Figure 2-2 shows a small part inspection unit.