contact the remaining penetrant layer. The action stops when the part is withdrawn from the remover, unlike lipophilic
emulsifiers that become active only after withdrawal and during drainage. Figure 2-20 illustrates hydrophilic remover
Figure 2-20. Action of the Hydrophilic Process.
The clean, preclean, penetrant application and penetrant dwell steps are identical in both the lipophilic and hydrophilic
methods. However, the processes diverge with the pre-rinse step in the hydrophilic method. The part is subjected to a
plain water spray following the penetrant dwell when using the hydrophilic method. The mechanical action of the
water spray removes over 80 percent of the excess surface penetrant, leaving only a very thin uniform layer of surface
penetrant on the part which helps optimize the removal process. It reduces the amount of remover consumed, and in
immersion set-ups, minimizes contamination of remover due to penetrant carry-over. It also reduces remover contact
time since, in general, contact time is about 50 percent less when the pre-rinse step is used. This pre-rinse step cannot
be used in the lipophilic process, as the oil base emulsifier does not tolerate water.
188.8.131.52.3.2 Pre-Rinse Procedure.
The pre-rinse step SHALL be used since it improves the efficiency of the process and minimizes hazardous waste. The
pre-rinse cycle SHALL be a coarse spray of plain water for 30 to 120 seconds, at a pressure as low as practically
possible, not to exceed 40 psig, with a water temperature of 50°F (10°C) to 100°F (38°C). The objective is to reduce
the amount of surface penetrant, while leaving only a thin layer remaining on the part.