Good day everybody.

Penetrant testing, like I said before, is one of the simpler NDT methods. It is also the easiest method to stuff up.

As you know we get three different types of penetrant. The most expensive and time consuming is the Post emulsified method. This method relies on you to apply a “soap” to the test piece after the penetrant dwell time, to clean the test surface from background that will mask small indications.

Luckily the Post emulsified method is not used on site and is just way too sensitive for our needs.

The background is the pink tint on the test surface, after the developer has been applied. Clients know that a pink test surface after penetrant testing is an indication of inexperience.

The most popular method is the water washable method. This penetrant has the soap pre-mixed into the can. This means that you apply penetrant and soap to the test surface at the same time. All you need is water to remove excess penetrant after the dwell time. We use this product on rough surfaces like welds or threaded components, just because it is easier to clean.

The last method is the solvent removable one. The penetrant has no soap pre-mix and can only be removed with a separate solvent wipe, something like acetone. It’s more sensitive than the water wash method, but used on smooth surfaces.

So what is the big deal?

When you use a solvent removable penetrant on a weld you put yourself in a very difficult position. You are using a more sensitive penetrant; thinking that you will get better results. The problem is the removal of the penetrant after dwell time.

Water will not work since there is no soap pre-mixed. A solvent wipe with a rag is the only acceptable way. But after 20 minutes of sweating, swearing and rubbing like a person possessed, you decide to spray solvent cleaner directly onto the weld just to remove some of the background, knowing what a pink background means for your reputation. You are effectively performing a pre-clean.

Then you apply the developer, step back and admire your handy work – all looks good. Signing the report “no relevant indications found” makes you feel warm and fuzzy inside.

You have removed penetrant from shallow surface cracks by spraying solvent onto the weld. You have effectively reduced the sensitivity of the test. That fuzzy feeling is your conscience telling you that you may have missed cracks and the possibility of a court case exists.

Select the correct product for the application people. You are qualified.

Published with the kind permission of Hennie de Wet