7/28/2019 hyd post

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Hydrophilic removers are applied by immersion in an aqueous solution. The concentration for immersion varies betweenthe range of 2.5% to 10%, 20% and up to 30 % depending on brands and conditions of agitation. The manufacturer of the emulsifier can provide the proper information concerning this concentration. Concentrations higher than recommendedby the emulsifier manufacturer or the qualified percentage is prohibited. The immersion time varies from 20 seconds to5 minutes depending on the penetrant, emulsifier concentration, surface roughness and agitation. The surface active agentin the remover combines with a small quantity of penetrant from the surface and prevents the penetrant fromrecombining with the remaining surface penetrant. A slight agitation is necessary to remove the colloidal suspension of penetrant – emulsifier from the surface and to expose fresh penetrant. The preferred method of agitation is mechanical. Agitation using compressed air can cause heavy foaming and may introduce contaminants. When application is byimmersion, hydrophilic emulsifiers malfunction as a result of penetrant accumulation. Contamination increases when partgeometry includes cavities, or areas which entrap penetrant to be carried over to the emulsifier tank. Emulsifier withlower concentration gets contaminated faster. The 30% concentration, if used, tolerates some three times more penetrantcontamination as the 10% concentration does. Everything being  equal, a 30% concentration lasts three times longer thana 10% concentration, and is economical because of less frequent disposals. Hydrophilic emulsifiers are infested byfungus and algae and the tanks must remain covered when not in active use. 30% concentration has more resistanceto this infestation. Hydrophilic remover solutions are also applied by spray or as foam. The concentration of the solution tend to be much

lower up to 5%. However, higher concentration may be used depending on the manufacturers recommendation.Immediately following the remover spraying, a freshwater rinse of the entire part is required to stop the action of anyremover remaining on the surface of the part. Hydrophilic removers minimize background fluorescence on part surfacesas well as bleed out of excess penetrant from hollow parts.The concentration of the detergent solution is critical to the success of the process and must be controlled. Water loss

in hydrophilic emulsifiers results in more concentrated and more active solutions, a cause for over-emulsification withresultant failure of the penetrant process. To monitor the concentration, the refractive index of the working solution isgenerally measured and compared against graphs generated by measuring the refractive index of solutions of knownconcentrations, using a Refractometer [ an optical device with a reading scale ]. A drop of the working solution is placedon the proper spot on the refractometer and a reading is made on the scale and then converted into percentage byusing a table or a graph applicable for the particular remover and supplied by the emulsifier manufacturer. The graphmay be generated in the workstation using prepared solutions of the standard remover from 50% of the workingstrength to 50 % above. A minimum of 5 solutions of different strengths should be prepared for this purpose. 

Compiled by K. Chatterjee, 75643  Center for NDT P 00 Rv 04 Self study material.

Post Emulsification Penetrant process : Advantages :   Disadvantages :Good on wide, shallow defects. Additional steps required in processWashes well after emulsification. for application of emulsifier.Short penetration time. Materials are more costly.

Good production, especially on large parts. Not as good as water – wash onNormally not affected by acids or chromates keyways, threads and rough surfacesSuitable for smooth surface. Usuall needs UV s stem.

Post Emulsification penetrants :  Hydrophilic emulsifiers or removers are water based viscous liquids andcontain blends of non ionic detergents, coupling agents, corrosion inhibitors anddyes. These emulsifiers are usually supplied as colored concentrates to bediluted in water to prepare the working solution. Hydrophilic emulsifiers functionby displacing excess penetrant by detergent action. The force of the water sprayor the agitating action in the dip tanks provides the necessary scrubbing actionwhile the detergent displaces the film of penetrant from the part surface. Theseemulsifiers are slower acting than the oily lipophilic emulsifier; therefore, it iseasier to control the cleaning process. Because it is incompatible with water, pre

rinsing prior to application of remover is recommended. The purpose of this stepis to drive off physically a large proportion of the surface penetrant so reducingthe quantity of penetrant to be removed by the detergent solution to a verysmall amount. Pre rinsing also leaves an even layer of surface penetrant.Immersion technique tend to be unsuitable for this pre - rinse operation.