In fact, Figure 1 shows a technician using helium to find leaks. Still, except for some high-vacuum systems such as autoclaves, or finding leaks on condenser water boxes, ultrasound can definitely get the work done.
Ultrasound is actually quite useful in locating condenser water box leaks. It may not be as sensitive as helium, but it has its advantages. For instance, there are occasions when helium is used as a trace gas, but it can be either extinguished or just blown away. For instance, I was once observing a technician using helium for leak testing a heat exchanger in Southern California. However, the Santa Anna winds were blowing that day and his trace gas was simply being blown away. Ultrasound would have been a good substitute for him, but some technicians are not familiar with the many applications for ultrasound.
Since ultrasound is sound above the human hearing range, it is a wonderful technology to use in noisy facilities. What is noisy to you and me cannot be heard by the ultrasound receiver. Therefore, the noise that prevents you and me from hearing a compressed air or vacuum leak can be filtered or tuned out of range, allowing the end-user to detect a leak like a vacuum or in-leakage, which is typically heard in the 38-40 kHz range.
Taking The Plunge
What? You say you haven’t tried ultrasound yet? When you do take the plunge, you will be amazed at the leaks you find using these instruments. I do encourage you, however, to make sure your instrument, or potential instrument, is well equipped to do what you need it to do. There are some basics to look for, so when purchasing an ultrasound instrument, choose an instrument that has:
• The sensitivity to hear in-leakage • The ability to reduce or filter out background noise • Various accessories to aid you in leak detection
I certainly don’t want you to feel as though leak detection is a walk in the park. Ultrasound’s beauty is that it is a simple technology to get started with and have early success. But it does take time to become familiar with your instrument, develop techniques, learn to filter out background noise, and learn how to use the technology for a wide array of leak detection applications. You need to seek out the necessary training to learn these techniques, and I suggest finding someone with in-field experience. Many of today’s sales reps are simply not familiar with many advanced applications, and have little, if any, case histories to share with you.
And Now...Back To The Leaks
Let’s consider in-leakage of an expansion joint in a power plant. These leaks can be found by using ultrasound. Within many generating plants an expansion joint leak may go unchecked, again mainly due to the fact that many technicians are unaware of an ultrasonic receiver’s sensitivity and potential for this application. These expansion joint leaks are considered by some to be just ‘weepers’, or defused leaks, and not worth the effort to find. However, ultrasound can be your best friend for expansion joint leaks, so don’t hesitate to use it.
Just ask Brian Thorp of Seminole Electric in Palatka, Florida, who recently used his U.E. Systems, Inc., Ultraprobe 2000 pistol and parabolic dish to hear a leak on an expansion joint some 25-30 feet away. I dare say that this leak might have, in fact, sucked the whiskers off his face had he been closer, but it was a good find never the less.
Many years ago, I trained Brian in the use of airborne ultrasound, for both his Ultraprobe and his SDT170. Ever since then, Brian has been a strong proponent of ultrasound technology to locate condenser water box leaks as well as steam leaks, compressed air, hydrogen and negative pressure leaks.
The precipitator penthouse (see Figure 2) is an area where ultrasound can pay large dividends. All of the flue gas passes here, and it is also where the electrostatic ash removal occurs. The precipitator penthouse should be tightly sealed and any casing cracks or openings (see Figure 3) that you find with your ultrasound instrument should be closed and/or sealed.
Vacuum Type Leaks
So, what is a vacuum? Theoretically, vacuum is space without matter in it. A perfect vacuum has never been obtained. The most nearly perfect vacuum exists in intergalactic space, where it is estimated that, on average, there is less than one molecule per cubic meter. A common, but incorrect, belief is that a vacuum causes “suction.” Actually the apparent suction caused by a vacuum is the pressure of the atmosphere tending to rush in and fill the unoccupied space.
This movement of air or turbulence may be detected with ultrasound. Turbulence is internal, therefore the sound is internal. Technicians typically have to move the ultrasound receiver or microphone closer to the leak to detect the leak. We sometimes describe this leakage as “vacuum” or “in-leakage”. In-leakage, is a term used freely in and around a power plant, as air rushes into a closed system due to cracks in casing walls, loose bolts on piping, deteriorated gaskets, or seals. These leaks often greatly reduce the efficiency of the generation plant.
According to Brian Harpster, INTEK Product Specialist, “It’s not unusual for condenser air in-leaks to cost a company between $3,000 and $5,000 a day, plus a loss of potential revenues in MW hours of $10,000 to $100,000 daily.”
“Most engineers and executives are surprised to discover how expensive air in-leakage can be, particularly when we define the potential losses they may face over the long haul,” says Harpster.
“Plus utilities never like to miss the opportunity to sell excess power back to the grid, especially at peak periods. Not only does air in-leakage contribute to back pressure on the turbine, which reduces system efficiency,” Harpster explains. “But back pressure may also be caused by vacuum pump partial failure, which may not be easily identified by a search for in-leakage. The ‘symptoms’ may go unnoticed for several months under conventional industry maintenance programs. With failing exhausters, dissolved oxygen and other noncondensibles quietly build up in the condensate.”
Mr. Harpster is referring to the use of the INTEK RheoVac Sentry that monitors in-leakage within the condenser exhaust lines. Whether you are monitoring through a system like this or manually surveying the plant for in-leakage using ultrasound, this fact remains – in-leakage is a serious problem, and knowing how to find, detect and remedy the leaks should be everyone’s concern.
Another point that he mentions is the noncondensibles. Dissolved oxygen in the system may require the system to be treated with costly chemicals that may possibly lower the life expectancy of certain components within the generation side. These impurities allowed into the system through leaks can and will cause corrosion throughout the boiler feed water system.
Accessories Can Help
Do you have an idea where to go look for your in-leakage? Do you understand how to use your instrument? Are you familiar with the accessories offered by the manufacturer of your instrument?
I sold ultrasound instruments at one time and was always amazed at how often technicians didn’t know about all of the accessories that were available. For instance, take the UE Systems, Inc., Close Focus Module. This little device allows the end-user to hear a vacuum or in-leakage with a little more amplification. The internal cone design amplifies the detected ultrasound up to 10-11% and has a narrow field-of-view. A great little accessory for examining switchgear or electrical panels, especially when, for safety, you need to stay back and not reach inside a cabinet.
You will notice that the technician in Figure 4 is using an SDT170 with a 31-inch SDT Flexible Wand accessory. This flexible wand accessory (also shown in Figure 5) is particularly valuable tool for this kind of inspection. The universal interconnect pigtail cable allows the technician to stretch some 8 feet away from a holstered or handheld base unit while listening through the headphones for leaks.
Learn how to work in and around competing ultrasound. Learn how to use barriers to block competing sounds. Learn how to use frequency tuning (if your instrument has this feature) to tune out competing sounds, or to tune-in sounds or frequencies that enable you to detect a leak.
Also, study hard to learn the many applications for ultrasound. Heat exchangers, condenser water boxes, boiler casing leaks, expansion joint leaks, soot blower air supply leaks and vacuum pump leaks are just a small representation of the many applications that await you.
In today’s economy, every single technician has to become leaner and more resourceful than ever before. Your job, and many other’s jobs, may depend on it.
Equally as important is considering the natural environment. A plant running as efficiently as possible is a clean burning plant. A clean burning plant is a greener plant.
Unless noted otherwise, all photos courtesy of Ultrasound Technologies, Inc. Jim Hall is the president of Ultra-Sound Technologies (UST), a vendor-neutral company providing on-site predictive maintenance consultation and training. UST provides an Associate Level, Level I & II Airborne Ultrasound Certification. Jim is also a regular provider of on-line presentations at ReliabilityWeb.com and is a contributing editor for Uptime Magazine. Jim has provided airborne ultrasound training for several Fortune 500 Companies in electrical generation, pulp & paper, petro-chemical and transportation (marine, automotive, aerospace). A 17 year civil service veteran, Jim served as an aerospace engineering technician for Naval Aviation Engineering Service Unit (NAESU) and with the Naval Aviation Depot Jacksonville Florida (NADEP). Jim is also president of All Leak Detection, LLC a leak detection company providing air leak audits above and below ground leaks. Jim can be reached at (770) 517-8747 or email@example.com