Penetrant Testing is relatively simple and cheap, but this doesn’t mean that we can disregard the basics.

Recently while doing Penetrant Testing outside – in broad daylight with a moderate wind – the client was not happy with me re-applying penetrant after 15 minutes of dwell time. He thought that I was wasting penetrant, which he had to pay for.

I had to explain to him that, although the lighting conditions were perfect – no cloud in the sky – the sun and the moderate wind would cause rapid evaporation of the mixed in solvent and paraffin carrier fluid in the penetrant. This results in the penetrant becoming thick and sticky, reducing its ability to penetrate cracks.

By re-applying fresh penetrant we reduce the viscosity (resistance to flow) of the penetrant. This ensures a thin liquid, able to penetrate fine cracks.

Recommendation: It is good practice to re-apply penetrant after 15 minutes of dwell time, even when the conditions are good. It may mean a bigger mess on the floor to clean up. The end result is a test that will find all possible defects and you can sign off the report with confidence.

Hennie de Wet