Water-washable penetrants (Method A) are available as Fluorescent (Type 1) or Visible (Type 2) pene-trants and in all sensitivity levels. The water-wash method is popular for several reasons. It is less ex-pensive, the process time is quicker, there are fewer processing steps and timing variables are reduced.
Water-washable penetrants work best on rough surface parts, threaded or grooved parts and those with holes and orifices, which may be difficult to remove with the post emulsification method. It is es-pecially suitable for automation, larger parts, leak testing and use on parts that are incompatible with oil-based systems.
Water-washable penetrants are removed by manual or automated water spray, manual wipe or air agitated immersion wash. If a manual spray is used, the water pressure should not exceed 40 psi; the temperature should be between 50 –100 F using a coarse spray at a minimum distance of 12 inches. Al-though water washable processing has its advantages, certain specifications will restrict its use because over-washing can occur in shallow discontinuities, which makes rinsing time critical to the process.
Recommended Developers for Water-Washable Penetrants
Developers increase the visibility of both the visible and fluorescent penetrants. They draw the pene-trant out of the flaws and spread the indication for brighter results. The developer you choose should be able to provide a good, uniform contrast; be easy to apply and remove; and work well with the penetrant chosen.Dry developers are the most effective for fluorescent water-washable penetrants. It is the easiest developer to apply. However, before using a dry developer, it is important that the part be completely dried after the rinse before applying the dry powder. It can be applied by immersion or by dusting with hand-held powder bulbs. In automated systems, developers are applied in a swirl cloud developer sta-tion. The use of a dust collector to evacuate the powder from the chamber is also recommended. A non-aqueous developer is a convenient solvent developer for portable fluorescent aerosol penetrant inspec-tions.
Water-soluble developers are not recommended for use with water-washable penetrants because it is possible that when used with these penetrants, it will act as an additional emulsifier and wash the penetrant away. Many specs will prohibit the use of these developers with water washable penetrants.
With visible water-washable penetrants, a non-aqueous or solvent developer is recommended be-cause it gives the best contrast to the penetrant.