Water washable penetrants are all classified into sensitivity levels based upon their performance.

The sensitivity levels as per ASTM 1417 and AMS264 are classified as:

• Sensitivity Level ½ – Very Low
• Sensitivity Level 1 – Low
• Sensitivity Level 2 – Medium
• Sensitivity Level 3 – High
• Sensitivity Level 4 – Very High

The reason for the various sensitivity levels of penetrant is mainly attributed to the need to have various levels of sensitivity to allow for the testing of multiple types of components, to which different levels are suited to the task at hand.

For example when testing an as cast rough surface whilst looking to identify large open defects such as inherent casting defects, a relatively low sensitivity penetrant would be the most suited to the inspection, this Is because a higher sensitivity penetrant would first of all be extremely difficult to wash off the surface of the parts and secondly the number of non relevant indications that would be picked up coupled with the excessive amount of background could actually reduce the sensitivity of the test.

On the reverse of this argument, if you were to be carrying out testing on a highly machined turbine blade with a smooth surface finish looking for stress cracking and micro fractures, a penetrant with a high degree of sensitivity would be the best penetrant for the task. A level 3 or 4 sensitivity penetrant would allow for the detection of even the smallest of surface breaking defects.

In addition to the penetrant sensitivity classifications penetrants are also further classified into Types which include:

• Type I – Fluorescent Dye
• Type II – Visible Dye

Penetrants are also classified depending on the method of penetrant removal from the components

• Method A – Water Washable
• Method B – Post Emulsifiable Lipophilic
• Method C – Solvent Removable
• Method D – Post Emulsifiable Hydrophilic

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