T.O. 33B-1-1
2-48
of residual penetrant will produce a higher background than the same quantity of a penetrant system with a lower
sensitivity level. It is necessary to remove more of the residual high sensitivity penetrant to produce an equivalent
background.
2.5.4
Removal of Water Washable Penetrant, Method A.
2.5.4.1
General Description.
Water washable penetrants are penetrants that contain an emulsifying agent. The excess surface penetrant is removed
with a water spray following the penetrant dwell period. The water washable penetrant is converted into small
suspended oil droplets by the mechanical force of the water spray. A separate process step of applying emulsifier is not
required. Water washable penetrants are often called "self-emulsifying" and are one of the most widely used non-
destructive inspection methods. Water washable penetrants exist in all penetrant system sensitivity levels.
2.5.4.2
Removal Procedure.
Water washable penetrant is removed after penetrant dwell by subjecting the part to a water spray wash. The spray
wash may be a hand-held nozzle, a semi-automatic system, or a fully-automated system. Care must be exercised to
prevent over-removal since the penetrant entrapped in discontinuities contains an emulsifying agent and is easily
removed. Removal is controlled by length of wash time and the wash must be stopped when an acceptable background
is reached. Figure 2-15 shows cracked chrome panels following different wash times. Insufficient wash, optimum
wash, and excessive wash are shown. The smooth surface of the chrome plated panel is deceptive. If the surface were
rougher, some residual background may have been retained on the optimum-wash sample. Water washing of
fluorescent penetrant SHALL be accomplished under black light. The wash station should be in subdued light, if
possible (20 lumens). Details on water washing are provided in paragraph 2.5.4.5.
