process control is the term used to define the quality control checks performed on a penetrant process to ensure optimal test results. The penetrant process includes the materials, the equipment and the procedures. The main reason for performing process control is to ensure that the penetrant process will detect the discontinuities that are required by the specification with repeatability and reliability. The results of good process control are a high confidence level in the quality and reliability of the penetrant process. The reliability of penetrant testing is dependent on the inspector and the penetrant testing process. Inspector must be fully qualified and motivated to perform vigilant test. After a part has been tested, it is often difficult to determine the quality of the test. Therefore, the reliability is dependent on the inspector.
In addition to the inspector, there must be an approved and qualified testing process. The penetrant process will be approved and qualified if meets certain sensitivity and repeatability test criteria.
To maintain the reliability of a penetrant test, management must take the necessary steps to perform quality control evaluations of the steps to perform quality control evaluations of the inspector and the process. Merely ensuring that an inspector is a level II may not be sufficient. Routine spot evaluations and made the use of sample defective parts can play a major role in maintaining confidence in the inspector and the process. Management must also take aggressive action to ensure that the equipment and penetrant materials are maintained properly.
Performance testing
The frequency of performance testing on penetrant process varies. Systems that are not used often do not require frequent performance testing; however, systems with heavy use require daily performance testing and possibly even before each shift. The important point is that the system be performance tested before processing parts.Performance testing is completed in two ways
(1)Process know defective parts and compare the results of the test with know and acceptable results
and (2) use crack standards in the form of panels or blocks to do comparison testing.
Performance testing using panels or blocks involves processing a know sample penetrant material and an in use or new sample of penetrant material at the same time. All conditions should be the same. The results are then compared and a determination is made about the performance of the system. Comparison testing is a valid and approved technique for checking system performance- However, care must be taken to ensure that the testing is carefully controlled.
Penetrant and developer samples must be protected on the part or panel and testing panels must be processed in the exact same manner.
Reference penetrant materials
The reference of standard penetrant is a sample of a know penetrant that meets the performance specifications necessary for the testing process. The size of the sample should be sufficient to be used for the life of the penetrant and to sample new penetrant. In addition to the reference penetrant, a sample of the developer should be kept. In both cases, the reference samples must be protected from conditions that would degrade them. Conditions such as high temperatures, plastic containers and sampling using contaminated devices are examples of conditions that will degrade and contamine the reference samples.