Iowa State University has done some work regarding penetrant testing. Individual topics on their work have been presented before, but this time it was all put together. We want to list some of the highlights of their work and to refer you to the places where you can look at the details of what they have done and the results that they obtained. We urge you to review the full scope of their work, which can be found at https://www.cnde.iastate.edu/research/epi/
The bottom line about cleaning is that the parts must be clean prior to penetrant inspection. This does not mean that only the surface must be clean, but that the surface and especially the cracks must be clean. There are many ways to do this and some procedures that should either be avoided or used with caution. It is beyond the scope of this newsletter to go into the many details
of the cleaning study, and we suggest that the full study is well worth reading on the above web site.
The main thrust of this investigation was to test the effect of increased dwell time on the ability to locate defects. The answer is simple. Longer dwell times are better than shorter ones. This was
found by comparing 2 hour dwell with 18 hour dwell. The study will continue by looking at dwell times of 5, 10, 20, and 30 minutes.
There are some mild surprises here. Variations in the hydrophilic emulsifier concentration within the range of ±5% did not have any effect that was important. What was found to be important was the contact time. Agitation was not found to be statistically different than no agitation.
The study of developers was extremely interesting and very revealing. The first part of the study concentrated on dry powder developer (form a). It was found that the several commercial dry powder developer chambers tested varied in their ability to adequately coat the parts, and that every chamber tested showed that the orientation of the part was very important in developing
the flaws. When the flaw is located on top of the part, it is found much easier than if the flaw is on the side or on the bottom of the part. Dry powder developer from different manufacturers was found to produce equivalent results.
The second phase of the developer study worked with the other forms of developers, specifically soluble (form b), suspendible (form c), and non aqueous (form d) developers.
One of the major findings was that using the soluble or suspendible developers at the recommended concentration produced far better results than using these at a lower concentration. Lower concentrations have been used with the idea that finer cracks would not be obscured by a thicker coating of developer. This premise was tested and found to not be true. In fact, using the recommended concentration produced a 240% increase in brightness.
For non aqueous developers, it was found that alcohol based developer was more sensitive than acetone based developer.
Last, a bar chart was developed that ranks the various developers and the way that they are used in terms of the brightness of the indications produced. This chart is very important and worth careful study, because it dramatically illustrates the differences among using different developers in different ways. We recommend it highly.
For those who were unable to attend the meeting at which this talk was presented, and who wish to hear it in person, it will be presented again at the ATA NDT Forum . The Forum will be held this year from September 19 to September 28 in Atlanta, Georgia.