Application of Remover.
The removal of excess surface penetrant using hydrophilic removers can be accomplished through the use of either
immersion or spray technique, or a combination of both. Each technique offers certain advantages along with
disadvantages that are discussed in the following paragraphs.
18.104.22.168.4.1 Immersion Technique.
a. Procedure. The primary advantage of the hydrophilic immersion technique compared to the spray
technique, is its effectiveness on hollow or complex geometry parts where the configuration interferes
with the spray impinging on the part surface. In use, the part or parts are immersed in the remover tank
while still wet from the pre-rinse. The principal mode of action is a detergent mechanism. A slight
agitation is necessary to bring fresh solution in contact with the surface. Agitation can be movement of
the part through the solution, but is most usually produced by an air manifold in the bottom of the tank.
Excessive agitation that is evidenced by foaming SHALL be avoided. Time of immersion depends on a
large number of factors and will vary between 30 seconds and 2 minutes. The maximum time of 2
minutes is seldom necessary, except on very rough surfaces or when remover is depleted.
b. Remover Concentration. Each penetrant manufacturer has its own formulation that varies in
aggressiveness. The concentrations of hydrophilic emulsifier (in water) used for qualification are
identified in the Qualified Products List (QPL) and should not be exceeded without approval from the
cognizant engineering authority. Caution must be exercised when changes in suppliers are involved
because the required concentration may change. Penetrant and remover are qualified as a system (see
paragraph 22.214.171.124) and SHALL NOT be interchanged.
c. Penetrant Tolerance. One of the disadvantages of the hydrophilic immersion technique is the remover's
limited tolerance to penetrant contamination. As parts are processed, the amount of penetrant in the
remover gradually increases. If the removal process is closely timed, penetrant contamination will
reach a point where a distinct performance change occurs. The amount of penetrant causing this
performance change is called the remover's penetrant tolerance point or level. The amount of penetrant
that can be tolerated is directly related to the concentration of the remover and sensitivity level of the
penetrant. Typical tolerance levels for a remover concentration of 33% is 5% to 6% for a Sensitivity
Level 3 penetrant and 3% to 4% for a Sensitivity Level 2 penetrant.
d. Bath Appearance. A freshly mixed remover bath is a transparent or clear, pink solution. During use,
as penetrant is removed from the parts and retained, the bath becomes turbid or cloudy with distinct
color change. As additional parts are processed and the penetrant tolerance point is approached,
globules of penetrant will rise to the surface, and then slowly disperse back into the mixture. This effect
is not usually noticed in an agitated bath, but is visible when the agitation is shut off. When the
penetrant tolerance point is reached, the penetrant will remain floating on the surface. A characteristic
of the bath is that the excess penetrant does not spread across the surface, but collects at the sides. The
remover will continue to function in this condition, but at a very reduced rate. A problem with using
the remover after the penetrant tolerance point is reached, in addition to the longer removal time, is the
tendency of the floating penetrant to deposit on the part as it is withdrawn from the solution. This
results in an objectionable background. If the bath is to be used after the tolerance point is reached, the
majority of the floating penetrant should be removed. This can be done by wiping the tank edges with
absorbent newspaper, paper towels, or rags.
126.96.36.199.4.2 Hydrophilic Spray Technique.
a. Procedure. Hydrophilic remover can be applied by spraying the part with a mixture of water and
remover. This method of application has several advantages: it does not require a separate tank; it
works well on simple contoured parts; and it can be easily automated. The procedures and equipment
are identical with those used in spray rinsing, (see paragraph 188.8.131.52). The usual concentration range is