Air Down Under: Controlling the costs of compressed air in underground mining
Compressed air can comprise up to 20 percent of the costs of underground mining, according to the Ontario Mining Association (OMA), and 20 to 40 percent of energy costs at mines can be attributed to compressed air systems. Given that up to 70 percent of that air is wasted through leaks, the problem of leaks in compressed air lines is one of the most costly and inefficient draws on the bottom line.
The numbers are staggering. The OMA’s compressed air leak management program report, “Implementing a Sustainable Compressed Air Leak Program,” demonstrates just how costly leaks can be: a single 1/2-inch-diameter leak, assuming energy costs of $0.10/kWh, can total to $12,820 throughout the course of a year for a one-shift operation and as much as $47,850 for a three-shift operation. Even the tiniest of leaks can add up: a single 1/16-inch-diameter leak can cost up to $200 over a year for a one-shift operation and up to $750 for a three-shift operation.
In a typical mining operation, leaks in compressed air lines can number into the hundreds, resulting in wasted energy costs upwards of $100,000 a year. The costs alone should be enough to consider a leak management program, but leaks also create other problems. Fluctuating system pressure can lead to inconsistent performance of the tools and equipment that operate on compressed air. Operation time may need to be increased to make up for the lower pressure, which can increase maintenance costs and reduce the service life of compressors due to excess load.
Leaks can occur at any point in a compressed air system and are blamed on a number of factors. Through regular mining activities, compressed air piping is exposed to vibration, impact and harsh materials, all of which could lead to leaks. Compressed air lines in the mining industry are typically joined using grooved mechanical piping due to the joining method’s ease of installation and maintenance, strength and ability to quickly adapt to changing mine geography. If the joints of a grooved system aren’t properly assembled, however, the gasket contained within the coupling housings can be a leak source. During its study, the OMA determined that pipe couplings are the most common source of leaks; approximately 60 to 80 percent of the air loss can be attributed to couplings.
Fortunately, the solution isn’t as drastic as replacing grooved piping systems, which mines rely upon to decrease installation and maintenance downtime and reduce total installed costs. The two primary causes of couplings as a leak source, pinched gaskets and incompatible gasket material, are easily fixed.
During coupling installation, a gasket can pinch, creating a leak path, if it’s not properly lubricated. Lubricating a gasket takes only a few seconds, but this step is often skipped to save time. If coupling gaskets are not pre-lubricated, personnel should take the time to lubricate the gaskets prior to installation, and managers should educate pipe installers as to the importance of doing so and the economic ramifications that result from leaks.
Mine maintenance personnel will try just about anything to save time, so adding a step to the pipe installation process may not be a welcomed idea. Installation-ready couplings, an alternative to traditional couplings, require fewer installation steps and decrease installation time compared to traditional couplings; they also reduce the chances of pinching a gasket upon assembly. Installation-ready couplings do not require disassembly prior to installation. The pre-assembled coupling is simply “stabbed” onto the pipe ends, and the bolts are tightened, like typical couplings, until the housing bolt pads meet metal-to-metal. Installation-ready couplings are offered in flexible and rigid styles in sizes up to 8 inches/200 millimeters.
The benefit of installation-ready couplings is twofold. First, they can reduce pinched gaskets during installation because the coupling is kept assembled and installed as a single unit, rather than piece-by-piece. Second, they can be installed in as little as half the time it would take to install traditional pipe couplings. As a result, installation-ready couplings meet owners’ goal to reduce costs and miners’ goal to save time.
Another cause of leaks at pipe couplings is gasket deterioration, which can occur when the gasket material is incompatible with, and not approved for the piping service. For example, when grade “E,” or EPDM, gaskets are used on compressed air lines, oil vapors present in the system can degrade the compound, eventually leading to a leak. EPDM is a commonly specified gasket grade, and is suitable for water services, but using this grade on air services can be problematic.
Oil separating filters are generally not used on compressed air systems, so the lines may carry oil vapors. As a result, grade “T,” or nitrile, gaskets should be used. This gasket grade is designed to stand up to air with oil vapors and will not degrade with exposure over time. Nitrile gaskets should not be used on water services, however, so mines will need to use two types of gaskets: EPDM for water services and nitrile for air services.
Replacing EPDM gaskets with nitrile gaskets on compressed air lines is not a quick maintenance procedure, but the cost savings that can be achieved through this method is significant. The OMA suggests conducting gasket replacement during maintenance to repair existing gasket leaks, and during installation of new compressed air systems.
Three mines participated in the OMA’s air leak management project as pilot sites. The mines saw almost immediate results in energy savings. In fact, two of the mines saved about $100,000 in annual operating costs just by fixing major air leaks. The project report, which includes lessons learned and best practices, is a must-read for every mine.
Fixing leaks attributed to gaskets within pipe couplings will not solve all challenges involving compressed air systems. After all, leaks can occur at multiple points along the line, and a big-picture leak management program is necessary to ensure long-term commitment to locating and repairing leaks. Such a plan, according to the OMA, should include recognition of the role of people and leadership, uses of equipment and instrumentation, and the development of new procedures and processes.
Nevertheless, proper selection and installation of pipe couplings play a major role in reducing downtime associated with leaks. Repairing leaks can reduce air loss to less than 10 percent of the mine’s compressed air output, resulting in immediate and significant cost savings.
Marc Carrière is the global mining market manager with Victaulic, a producer of mechanical pipe joining systems. For more information, visit www.victaulic.com.