or an emulsifier. Water-washable penetrants contain an integral emulsifying agent when received from the
manufacturer. This permits direct removal by water immediately after the penetrant dwell.
Postemulsifiable, Lipophilic Method.
Penetrants used in the postemulsifiable, lipophilic method are formulated to optimize their penetrating and visibility
characteristics. They do not contain any emulsifying agent and cannot be completely removed with plain water.
Removal is made possible by applying an emulsifier in a separate process step. This converts the excess surface
penetrant into an emulsifiable mixture that can be removed with water. (See paragraph 18.104.22.168).
Solvents used may contain aromatic, aliphatic, or halogenated compounds.
Aromatic compounds are characterized by a strange aroma and are formed from
hydrocarbons and benzene. Aliphatic compounds are derived from fat; paraffin is
an example. Halogenated compounds are materials in combination with the
halogens fluorine and/or chlorine. Many solvents are highly flammable while
others may decompose at elevated temperatures. Keep all solvents away from heat
and open flame. Vapors may be harmful. Use adequate ventilation. Avoid contact
with skin and eyes. Do not take internally.
The term "Solvent Removable" applies to the process rather than the penetrant material, since all penetrants can be
removed with solvents. Usually the penetrants used in the solvent removable process are the postemulsifiable
penetrants; however, water washable penetrants can also be used.
Postemulsifiable, Hydrophilic Method.
The postemulsifiable, hydrophilic method also uses penetrants requiring a separate emulsifier. The penetrants are the
same as those used in the lipophilic method. The difference between hydrophilic and lipophilic methods is in the
emulsifiers. Hydrophilic emulsifiers are water soluble emulsifiers and actually remove excess surface penetrant by
means of a detergent action rather than an emulsification action. (See paragraph 22.214.171.124).
Forms Of Developer.
There are four forms of developers in general use:
a. Dry powder
b. Water soluble
c. Water suspendible
There are several methods of applying each form of developer, e.g., immersion, fog, air bath, electrostatic and pressure
Classification Of Penetrant Materials And Processes.
ASM 2644 -Categories.
In ASM 2644, penetrant materials have been classified under several headings (See Table 2-1):