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 the presentation, which included both the scientific and technical details of the inspection method, and a textual description of how the method is used. There is no question that both the technical details and the descriptive text are important to present, but we have a preference for first describing the inspection method by text, and then following with the scientific and technical details. Our preference is based on a couple of reasons. Inspectors using penetrant inspection are not usually equipped to understand the math, physics, and chemistry that underlie the inspection process, and beginning a discussion of the method with formulas and scientific details could easily lose a non-technical reader by glazing his or her eyeballs. But even more important, one can become a very skilled inspector without understanding the science that underlies it.

We think that this is similar to many other things in life, where we have become accustomed to natural processes without understanding the science that makes them what they are. To describe a situation that almost anyone can relate to, we decided on a description of how a bicycle works so as not to fall. One can easily describe how to ride a bike and to teach almost anyone that technique, and to do so without getting into the physics involved. But ask any experienced rider what keeps the bike upright and you will either not get an answer or you will get an answer that is probably incorrect. Does this lack of scientific knowledge about the bike affect how one rides? That is a rhetorical question, and probably most of the riders in the Tour de France lack this knowledge, but still are among the best riders in the world.

We were not sure about the bike science, so we went to the internet and Google. What we found surprised us, but was very illustrative about the text presentation in the Penetrant Handbook. Here is a quote from the internet:

“Bicycles and motorcycles are both single-track vehicles and so their motions have many fundamental attributes in common and are fundamentally different from and more difficult to study than other wheeled vehicles such as dicycles, tricycles, and quadracycles.[4] As with unicycles, bikes lack lateral stability when stationary, and under most circumstances can only remain upright when moving forward. Experimentation and mathematical analysis have shown that a bike stays upright when it is steered to keep its center of mass over its wheels. This steering is usually supplied by a rider, or in certain circumstances, by the bike itself. Several factors, including geometry, mass distribution, and gyroscopic effect all contribute in varying degrees to this self-stability, but long-standing hypotheses and claims that any single effect, such as gyroscopic or trail, is solely responsible for the stabilizing force have been discredited”.

So in the case of the bike, there is no simple answer, yet riders hardly know this and can still become skilled. We believe that the Handbook presentation is best presented in descriptive form first, followed by the scientific data for those equipped to understand it and interested in it. This is what we have recommended.