Water Pre-rinse

ASTM E-1417 states (Paragraph that “Hydrophilic post emulsifiable penetrant shall be removed with a water Pre-rinse, application of the hydrophilic emulsifier and then a post-rinse.” There is an unanswered question as to whether this applies equally to both immersion in the emulsifier and to emulsifier that is sprayed on. Read More

Shelf Life vs Tank Life

We frequently get questions concerning the shelf life of our products. Shelf life is a term that can be defined differently by different manufacturers, and we explain what is the practice for Met-L-Chek. This information is also contained in the literature on the Met-L-Chek web site. Met-L-Chek Company defines shelf… Read More

Penetrant Viscosity

Penetrant Viscosity It is easy for some of us to speak about “old times” in the penetrant business. In the early days, which implies something like 30 or 40 or 50 years ago, one of the requirements of the QPL was to list the penetrant viscosity. Certificates of compliance with… Read More

Surface Roughness

We get a wide range of questions, from the sublime to the ridiculous. But we always understand that the question, no matter how “far out” it might seem, is an important one for the person who has asked it, and we treat it that way. Our days are livened by… Read More

Hydrophilic Emulsifier

Hydrophilic Emulsifier We probably do not say enough times that the subjects that are addressed in this publication originate with those folks who use penetrants. The last issue featured information about hydrophilic emulsifiers, and as usual, we received comments on the article. We relish receiving comments, because they come from… Read More


Here again, there is a lot of common sense involved. One should simply see that junk- oops, foreign material – does not get into the penetrant. But it does happen. There is the obvious poor practice of people throwing stuff into the tank. We are told that tanks have been… Read More

Mixing Batches

We do not know to what extent this subject is a problem for anyone in the USA, but it seems to have come up in Europe. There is a lot of common sense involved in this subject, and probably most, if not all, of our readers will agree with that. Read More

Hydrophilic Emulsifier Concentration

Hydrophilic Emulsifier Concentration This subject comes up from time to time and it is time to discuss it again. The hydrophilic emulsifier is used in method D post emulsifiable penetrant inspection. It is supplied as a concentrate, and needs to be diluted with water. This is where problems can arise. Read More

Flash Point vs Auto-Ignition Temperature

We have often looked to other NDT practitioners for input for Penetrant Professor articles. In this case we are basing the article on the newsletter put out by two knowledgeable French friends, Patrick Dubosc and Pierre Chemin. Over the years we have heard these two physical parameters being mixed up… Read More

Is Water Washable The Same As Water Based?

Is Water Washable The Same As Water Based? We recently had a customer call who was being pressed by an auditor to prove that the level 3 water washable penetrant he was using, (Met-L-Chek FP-923), was not a water-based penetrant. Being pressed by an auditor is nothing new to hear… Read More

What Is The Smallest Crack You Can Find?

What Is The Smallest Crack You Can Find? The proof of the pudding that this newsletter is driven by its readers is much more obvious to us than perhaps to the readers. But a sterling example has just occurred, as a reaction to a recent article in the May 2014… Read More

Pesky Penetrant Contaminants

Pesky Penetrant Contaminants Although the major components of penetrant inspection products usually cause no problems with the metals with which they contact when used correctly, there are some minor contaminants that can cause problems and which must be limited in certain applications. The  governing specification, SAE AMS 2644E, has taken… Read More

Indication Brightness

Indication Brightness In the last issue of this newsletter, we discussed the work being done at Iowa State University with regard to penetrant inspection. To  reiterate the place where you can get all of the detailed information presented at the Spring ASNT meeting, go to www.cnde.iastate.edu/faa-casr/fpi/ Once at this site,… Read More

How to reduce the amount of penetrant background on a rough surface …

One of the services that Met-LChek provides to the NDT community is the writing, updating and editing of the various specifications and procedures related to penetrant inspection. This includes the ASNT Penetrant Handbook, which is presently undergoing updating. While reviewing the text that has been proposed, we were struck by… Read More

Low/High Temperature and Penetrants

This subject was discussed in our 2nd anniversary issue of the Penetrant Professor in 1995. Funny how time flies but the questions remain the same. Every penetrant manufacturer is asked about what temperature their penetrant should be used at. In the case of Met-L-Chek penetrants, the label on the aerosol… Read More

The Evolution of Penetrant Specifications

A Few More Thoughts On The Evolution of Penetrant Specifications The past two issues of the PENETRANT PROFESSOR have concentrated on the historical path of the relevant qualifying documents and the journey to develop a method of measuring absolute sensitivity. While these have been extremely important in the creation of… Read More

Penetrant Application & Sensitivity

Penetrant Application & Sensitivity How is the best way to apply penetrant, and does the method of application have any bearing on the sensitivity of the process? This is a question that arises from time to time. It is not a question about the sensitivity of the penetrant, which is… Read More

Solvent Remover Does Not Contain Chromates

Bad Stuff Out We recently had a request from a customer who wanted to know how he could be sure that our solvent remover contained no chromates, since this seemed to be a requirement of NADCAP. We advised him that one could not have a product listed on the QPL… Read More

The Dilemma of How to Measure Sensitivity

The thermally cracked aluminum panel was an early method of comparing the sensitivity of one penetrant to another, and was written into the first issue of MIL-I-25135. At that time there was apparently no concept for a specific and identifiable method of quantifying absolute sensitivity, and the panel was solely… Read More