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Leak Detection Using Spectrally Tuned Infrared Imaging
BY BOB BENSON

New technology is opening doors in leak detection. The deployment of infrared imaging cameras in predictive and preventative maintenance is not new. Specialized, spectrally tuned IR cameras capable of vapor detection and leak visualization, however, are a very
recent development.

Over the past decade infrared sensor technology has matured. Its origin as high-end, military-use-only hardware was dictated by its cost and availability.

As the defense industry demanded higher insensitivities in their camera systems, cheaper more reliable gear, and production volume manufacturing, the IR sensor became an accessible technology for the rest of us. The science required for using infrared imaging in leak detection is nothing new.

The field itself has traditionally been dominated by astronomers of all people. What do astronomers and the LDAR,(Leak Detection and Repair) community have in common? They both want to see gases and vapors; the astronomers want to see them in far-off regions of the galaxy, while the community is obviously concerned about them closer to home.

As astronomers began realizing they could use IR imaging for extraterrestrial gas detection in the early 1980’s, the rest of us went on without giving it too much thought. The cameras they deployed were bulky, used cryogenic liquids to cool them off, and were prohibitively expensive. Thus, most systems were reserved for wealthy collegiate institutions with large alumni populations.

Then came 9/11. The U.S. Government made significant strides in the arena of homeland security in the wake of the attacks. Their large driving desire for IR surveillance systems nationwide lead to a radical decline in pricing as IR camera volumes exploded. This made sensors and IR cameras whose sensitivities were designed for counterterrorism available for commercial adaptation.

The application of vapor imaging and leak detection using a dedicated high-sensitivity IR imaging system followed within a few years. Scientists and engineers who had designed and deployed IR cameras for the U.S. Government turned their attention toward a substantial problem for the LDAR community—leaking vapors.

The detection of a vapor leaks has until now been the province of gas analyzers—the so-called “sniffers” of the world. In fact, with no other technology available to them, the LDAR community was forced to embrace this technology, which itself is not geared toward the desired goal of finding leaks.

Rather, a sniffer merely draws in air and lets you know the concentration of any additional vapors you might have been lucky enough to pull into the machine; it cannot tell you anything about where they came from or how much might be leaking at that break. It simply indicates whether or not it happened to suck up some vapor during the last sniff.

IR imaging is a stark contrast to the sniffer approach to finding leaks. If “A picture is worth a thousand words” then a motion picture ought to equate to a novel. Vapor imaging cameras literally show you live video of a leak in progress. They indicate precisely where the leak is coming from and even its approximate size. You do not even need to physically approach the leak site if you do not want to; the available zoom optics can take you up close.

These types of imagers do not use concentration as their means of vapor detection but rather mass, or more precisely mass flow. Since leaking mass is, after all, what a crew needs to stop by making some kind of repair, it seems only natural to deploy a technology that shows the user precisely that information.

As these imagers become more ingrained in the LDAR community, work practices and regulations are sure to follow. One must ask the logical question, “Why continue using current work practices that were developed for sniffing technologies when you now have at your disposal a means to actually see a leak?” The current practices do not really find leaks, they simply measure the air quality near potentially leaking equipment.

If you do not know something is leaking in the first place, finding it with a sniffer, tracking down where it is coming from, and fixing it, can be a monumental task. In the end, you will have to make a “best guess” as to what needs to be repaired and then hope whatever you do to affect a repair fixes the leak. With IR imaging systems, however, there is really no more guess-work. It shows you the leak even if you were not looking for it, and lets you know if you have made an effective repair afterward.

As one of the scientists responsible for this technology, I am often asked by interested individuals “What is the minimum concentration that this technology can detect?” My answer is, of course, that we do not see concentration. I then remind the inquisitive person that the concentration coming out of a leaking part is 1 million parts per million.

Using concentration as a yardstick is simply not what you need to perform LDAR effectively. What you really want is a tool that gives you the precise location of a leak even if you had no clue that a leak was present to begin with.

It should also show you, relatively speaking, how bad the leak is, and it should do this quickly without the need for exposing yourself to any health risks such as accidentally standing in an explosive vapor cloud.

This usually gets their attention and they start thinking about why sniffers have been used in the past and what is really going on when leaks are detected and repaired. Suddenly it dawns on them that they have been using a butter knife to turn a screw; a different tool could do a better job.

It is estimated that 84 percent of the mass leaked comes from only 0.13 percent of the leaking equipment. To make an immediate and meaningful impact on LDAR, just find and fix those 0.13 percent leaking components. If you spend 90 percent of your time looking for small and what I would call “nuisance” leaks (as is the current work practice), that leaves only 10 percent of your time to look for the majority leakers. Finding those should be the priority, and it should be set forth in both work practice and regulation. That saves the product, and the environment, and it might save your life.

What is next for IR imaging? Speciation and quantification? Probably. As this technology gathers steam throughout the commercial LDAR industry, it will no doubt be improved. More resources will become entangled in its use and the level of technical benefit it brings to leak detection will grow accordingly. FSM
Robert Benson is senior scientist for FLIR Systems.