Procedure

Steps of test procedure

  1. Pre –cleaning
  2. Penetrant application
  3. Excess Penetrant Removal
  4. Drying phase
  5. Developer application
  6. Inspection

 

1. Pre-cleaning

The test surface have to be free of any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or could cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapour degreasing, or media blasting. The goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may "work over" small discontinuities in the work piece, and an etching bath is recommended as a post-blasting treatment.

In particular, please pay attention that the test surface is completely dry before you go ahead. After drying, the pre-cleaning has been completed.

2. Penetrant application

The penetrant can be applied by various techniques, for example by spraying, brushing, rinsing or dipping. It is essential that the complete test surface is covered with penetrant. As soon as the whole test surface is covered the penetration time starts. The penetration time depends on the test surface and also of the ambient temperature. At low temperatures, the penetration shall automatically be extended. The test temperature may range from -20 ° C to 100 °.

3. Excess Penetrant Removal

The penetrant has to be removed completely from the surface. This can be done by rinsing or washing with water or e.g. by a solvent based cleaner by using a wipe. It must be ensured that the penetrant isn’t washed out of the defects (over washing).

4. Drying phase

After removal of the penetrant, the surface should be dried with compressed air, a lint-free cloth or by a n appropriate drying oven. When using a solvent based cleaner that dries due to highly volatile components by evaporation, the drying process can apply.

5. Developer application

Immediately after drying, the developer is applied evenly and as thin as possible. Very suitable for that are aerosol spray cans or compressed air spray equipment’s. Here usually it is distinguished   between airbrushed - and airless systems.

The developing time depends mainly on the temperature of the test surface. At low temperatures, the development period shall be extended, at high temperature it can be shorter.

6. Inspection

 After the developing time is finished, the test area is checked for indications in the developer layer. If fluorescent penetrants are used, the inspection has to be done under UV – ligt.

The indications are forming at the beginning red lines or points, which can crow out in larger indications during the development period (bleeding out).

There are just very limited possibilities to gather on the width or the diameter of an indication. To gather on the depth of an indication is impossible.