There has been no shortage of innovations in leak detection design since Uson first developed automated leak testing methods for the U.S. space mission a half century ago and then brought these techniques to various commercial applications. Last year, for example, Uson unveiled a leak tester that is so versatile it can perform nearly a half-billion permutations of leak, flow, or other nondestructive tests (NDT).
That said, it is the laws of physics that remain and always will be the primary driver of nearly all leak test specifications—from selection of test methods, to optimal test cycle-times at specific pressures, and more. When you know the relevant physics inside and out because you live and breathe leak testing 24/7 (or at least it feels like 24/7), it doesn’t take too long to rapidly identify the best leak test methods, technology components, and other options to tailor leak tests to the application at hand. Uson, for example, has a Leak Detector Express Proposal system that usually takes 48 hours or less, and fully or semiautomated turnkey leak-testing assemblies are usually two weeks or less.
What slows the quick turnarounds on leak detector selection or systems design? Sometimes there are inherent complexities, such as needing to design tests of moving parts or testing subcomponents in varying and wide-ranging pressure conditions. However, as this article’s headline foreshadows, the common “show stopper” is when the requests for leak detection equipment come with unreal leak rate specifications.
One example that comes our way every once in a while is the request for a “no leak” solution. From a physics standpoint, there is no such thing. When you drill down to the molecular level of any component or product with a sealed orifice, or one made from cast or molded materials that could not even be described as “porous,” it is physically impossible to attain a leak-proof standard. Just ask the folks living near a mountain proposed to be a burial ground for radioactive waste. More objectively, know that it is a law of the universe that when there is an opening, molecules will flow through that opening at a certain rate. The question is whether the rate of molecular flow is significant enough to impact a product or component’s intended functionality. In the aerospace industry, for example, leak rates are usually expressed in terms of standard cubic centimeters per second (SCCS). In most industries where leak rates are important, acceptable standards are typically expressed in terms of standard cubic centimeters per minute (SCCM).
So, when someone requests a “no-leak” solution from a leak testing specialist who certainly knows the laws of physics determining leak rates, it signals immediately that it is time to take the conversation back a step or two. How must the product or component function? And in what conditions, e.g., temperatures, pressure, fluid viscosity, other? What will be its physical orientation? Often, by the way, these requests end up being ones with relatively forgiving (larger than average) acceptable leak rates.
In part two of this series, I’ll talk about another commonly mistaken expectation for leak testing: the requests for accuracy and precision that are orders of magnitude stricter than what real-world requirements for measurement accuracy truly are.