Guide to choosing a Fluorescent penetrant

Water Washable Fluorescent (Type I)

Water washable penetrants are the most widely used for general metal working and even low stress component aerospace applications. Water washable penetrants are composed of water washable ingredients. The penetrant covered part is simply washed after the prescribed penetration dwell time. Being water washable, excessive wash time or pressure must be avoided with Method A penetrants to avoid washing the penetrant from shallow open discontinuities.

Post Emulsifiable   

Post emulsifiable penetrants and emulsifiers are qualified to the AMS-2644D specification and must be used together as a family of materials. Method B (Lipophilic) employs E-57 as the emulsifier, which is used as supplied. Method D (hydrophilic) uses E-58D, which is used diluted in water to a concentration of 17-20 % for immersion applications and < 5 % for spray. Most aerospace engine OEM’s use, or recommend the use of Method D. Met-L-Chek Company’s level 2, 3, & 4 Method D materials are approved by GE, Pratt & Whitney, and Rolls-Royce turbine engine groups. Met-L-Chek Company offers sensitivity levels 1-4, but for most applications requiring level 1 and 2 sensitivity, water washable Method A penetrants are generally used rather than the post emulsifiable. Even level 3 water washable is recommended over Methods B & D for everything except critical high stress or rotating hot section turbine engine components.

Emulsifiers & Removers

Aqueous Cleaners are widely used for both pre and post penetrant inspection cleaning. They are employed in cabinet spray washers, agitated soak tanks, steam cleaners, ultrasonic cleaners and manual wipe applications. Most aqueous cleaners are slightly alkaline and contain surfactants for effective wetting and removal of oily soils, loosely held particulates, and films. The most effective aqueous cleaners are a balance of additives that clean off the soils while inhibiting base material attack and are environmentally more friendly than the strong chemical cleaners. In spray systems they are used at lower concentrations than in dip or tank applications. Temperatures to 160°F (71°C) often are recommended to accelerate their cleaning action, although most will work at ambient temperatures with an increase in contact time. Aqueous alkaline cleaners are often used prior to more aggressive chemical cleaners . This is done to reduce the soil loading of the chemical cleaner tanks. Aqueous cleaners have been effectively used to replace vapor degreasing and solvent cleaning.


Evaporation rate should be considered when choosing a cleaner remover. When wiping the penetrant residue from a rough surface the slower evaporating remover will keep the wiping media moist and more effective at helping the removal of the penetrant. In the case of verifying a fluorescent indication by wiping the indication with a cotton swab or brush moistened with the remover, the slow evaporating material will make the indications blurry and bleed excessively. In this case a very fast drying cleaner is the right choice. When used as cleaners for pre-cleaning the inspection surface the slow material will not evaporate readily from the part and could interfere with penetration of the discontinuity by the penetrant. The faster drying cleaners are also better solvents for oils and greases improving their removal from the part. Tam Panel or starburst indication cleaning is best achieved with the directional spray tube applicators used on R-503 and R-504. All of the cleaners are flammable and should not be used in confined areas without proper ventilation. They should not be used near open flames or sparks. Nonflammable solvents, have been used in past years, but have been found to be carcinogens or are banned as Ozone Layer Depleting Substances. Flammable materials have been used for years and can safely be used with common sense and good industrial practice.


Developers are qualified to AMS-2644D. The use of a developer is required by most testing specifications. The developer draws the penetrant from the flaw site and creates a uniform surface on which to view the penetrant indication.