T.O. 33B-1-1
2-37
2.4.5
Application of Penetrant.
2.4.5.1
General.
CAUTION
Care must be taken to avoid trapping air bubbles or pockets during penetrant
application to complex shaped parts by immersion. Oil and air passages and blind
holes should be plugged prior to penetrant application by immersion. Remove the
plugs immediately after the inspection process.
Penetrant can be applied by any of several methods: immersion or dipping, spraying, brushing, swabbing or flowing.
The method to be used depends on several factors, including size, shape and configuration of the part or area to be
inspected; accessibility of the area to be inspected; and availability of inspection equipment. All methods of application
are acceptable provided the surface or area to be inspected is completely coated with penetrant. However, there are
certain conditions that must be met for each method.
2.4.5.1.1
Immersing or dipping is the preferred method of applying penetrant when the entire surface of a part must be inspected.
The method is limited by the size of the tank or penetrant container. Parts can be immersed one at a time or, if small,
can be batch processed by placing them in a basket or rack. When parts are batch processed in a basket, they must be
separated from each other during the immersion and dwell period. Contact between parts interferes with the formation
of a smooth, even coating of penetrant.
2.4.5.1.2
Certain part conditions require special attention during application of penetrant by immersion. Parts containing
concave or recessed surfaces can trap an air bubble or pocket when immersed. Air bubbles or pockets will prevent the
penetrant from contacting the part surface. Complex shaped parts should be inverted or turned over while immersed to
dislodge any entrapped air. Precautions must also be taken when immersing parts with air cooling or oil passages and
blind holes. During immersion, the passages and holes will fill with penetrant that will bleed out during development
and obscure an discontinuities in the area. In addition, it is difficult or impossible to completely remove penetrant from
passages and blind holes following inspection. Therefore, oil or air cooling passages and blind holes should be plugged
or stopped off with corks, rubber stoppers or wax plugs prior to immersion in penetrant. These devices SHALL be
removed immediately after the inspection process.
2.4.5.2
Application by Spraying.
2.4.5.2.1
General.
Penetrant, emulsifiers or removers, and wet developers may be applied by any of several hand or automated spray
methods. Spray application is especially suitable for parts too large to be immersed, conveyor lines, automated systems,
on-aircraft inspections (portable), and when only a portion or local area of a large part or component requires
inspection. In applying penetrant by the spray method, the requirement is to apply a thin layer that completely covers
the area to be inspected. Application of penetrant by spraying has several advantages over the immersion method. It is
usually more economical since large tanks of penetrant are not needed, and pooling of penetrant in part cavities is
reduced. In immersion application, pooling removes substantial amounts of penetrant by drag out.
