Qualified products Listing PT

AMS-2644 (formerly MIL-I-25135) requires qualification of all penetrant products to be used on military contracts. Commercial products to be used on military contracts. Commercial products with well documented properties are designated as reference standards. Many of the test requirements (sensitivity, fluorescent intensity and removability) are comparative.
The material to be qualified and the reference standard material are processed simultaneously under the same conditions and the results are compared. The material to be qualified must equal or exceed the reference standard material´s performance. Materials found to be acceptable are listed on a qualified products list. QPL-SAE-AMS-2644.

The listing of a material on the qualified products list does not guarantee that subsequent batches of product of the same formulation will be acceptable. The listing only indicates that the original raw materials, formulation and compounding practice can result in an acceptable product. There are many factors and conditions in compounding and manufacturing penetrant materials that can reduce their performance. many users routinely verify the performance of each incoming batch of penetrant materials.
Penetrant Properties.
Formulation of a liquid penetrant is a complex process because of the numerous and frequent conflicting requirements. High on the list of requirement is the ability to enter or penetrate and fill voids that contain tight or small surface openings. This conflicts with the need to be able to remove the excess surface penetrant.
Another requirement equal importance is the visibility or contrast between the penetrant indication and the surface background. Dye added to the penetrant solution helps to provide the necessary contrast between the indication and the surface background. To accept the dye into the penetrant solution, the penetrant must have a high solvent ability. This tends to conflict with the requirement of a high flash point, 93ºC (200ºF), to permit its use in open tanks and a relatively low evaporation rate for longtime storage in open tanks.
Unfortunately, there is neither a fixed rule for formulating a liquid penetrant nor a set of criteria that will provide a satisfactory product. However, there are some fundamental prerequisites that are necessary for acceptable performance. The penetrant must:

1. Be capable of smoothly and evenly distributing itself over the surface of the part to be tested- it must be able to wet the surfaces of the more common metals-
2. Be capable of entering and filling surface opening even though they may be very small
3. Resist removal and remain in discontinuities during removal of excess penetrant on the surface of the part
4. Be capable of exiting from the  discontinuity after the excess surface penetrant has been removed
5. Have high visibility or contrast in small quantities or thin films when viewed on the part surface
6. Not etch, corrode or otherwise degrade the part
7. Be Nontoxic