How do leaks impact the compressed air or inert gas system, causing a monetary loss? How can leaks affect the environment and, possibly, the well-being of the personnel working in close proximity to the leaks? We'll discuss how to approach leak audits and how to identify and address the leaks once they've been found.
Compressed Air Leaks
Precise control is critical to the products we produce and to the indoor environments we seek to maintain. Control and pressure-reducing valves manage compressed airflow to the manufacturing process and loose connections, splits in the control and sensor tubing, and ruptured diaphragms in control valves all have the ability to adversely impact process control. For example, biotech facilities may use compressed air to precisely maintain humidity and temperature within a controlled environment. If the humidity level goes awry in a controlled biogenetic research facility, it can ruin months or years of research. To avoid process inefficiencies, facilities should perform compressed air/gas leak audits on a regular basis or make arrangements with a competent and professional firm to perform periodic audits.
In a compressed air and gas system many critical components require validation of proper operation. Noncritical system components likewise need to be scanned and tested for leakage. These include, but are not limited to, relief valves, solenoid valves, flange gaskets, thread connections, filter/lubricator/regulators, welds, threaded connections, and quick-connection devices. At any given time they may be wasting energy and sacrificing proper process control.
Compressed air systems supply clean, dry air to their equipment and components. Separators, receiver vessels, compressors, and other components in a compressed air system use drain traps to automatically discharge the condensed water from the system. When a drain trap fails in the closed position it causes a backup of condensate and the air fed to the system will contain water, resulting in dust, dirt, and corrosion. If a drain trap fails in the open position large quantities of energy are wasted. Because most drain traps are piped into discharge manifolds and then to waste drains, it is not generally apparent from a visual exam that they might have failed in the open position. Therefore, it is essential that regular ultrasonic tests be performed on these drain traps.
Valves, solenoids, and other sensitive equipment can plug up or stick in an open position and eventually fail. Many times the gaskets between banks of solenoids begin to leak when water has not been drained from the compressed air system. Sometimes oil in compressed air systems can cause O-ring or gasket failures. If part of the system is outdoors and is subject to low temperatures, the air lines and the equipment to which it leads can freeze, causing cracks and permanent damage. A proper air leak audit should identify the components that are causing energy loss.
Gas Leaks: Costly and Dangerous
Other gases are more expensive than compressed air. The rule of thumb for contrasting a compressed air leak vs. a nitrogen leak, for example, is that typically nitrogen is ten times more expensive than air. So who wants to live with even tiny nitrogen leaks? If the leaking gas is volatile, such as natural gas, identifying and repairing the leak becomes an urgent priority. For example, in one plant I found 22 natural gas leaks in one section of piping near the ceiling. The gas line was feeding an oven that had ignition points every 10 feet along the length of the equipment. If an explosion had occurred—aside from the physical harm it could cause workers in the immediate area—it would have shut down the plant for quite some time.
Inert gases such as argon, helium, and nitrogen are nontoxic and do not burn or explode. However, they can cause injury or death when they are present in high concentrations because they displace the oxygen in the air. In a parts manufacturing plant I found a huge argon leak at a hairline split in the feed line carrying the gas to a welder. Leaks must be found and corrected before a small problem becomes a severe problem. In this business there is old truism: "everything leaks, it is just a matter of when."
Leaks also translate into the loss of cold, hard cash. Without a leak identification and repair program, leaks will add a hidden cost to the products your company produces, negatively impacting your company's ability to compete and affecting its profitability.
Is an Air/Gas Leak Audit Cost-Effective?
Leak detection is important in plants of any size. In a smaller plant your financial survival and competitiveness are even more important. For larger plants, the impact may be exponentially more costly. When I perform an audit in a large plant, I typically find leakage-caused losses of between $5000/day and $10,000/day. Once you repair your leaks, it is not unusual to find that you can shut down an extra compressor, with the cost and energy savings that entails. How often should a leak audit be performed? Most of my customers want the audit done semi-annually or at least once a year.
Enlist the Help of Department Employees
When leaks are large enough they can become audible without the need for ultrasonic scanning. Heighten the awareness of all individuals in each department. Ask them to report leaks that may be audible. If you do not already own ultrasonic leak detection equipment, consider purchasing some and training one or more individuals in each department to perform their own leak audits. An investment in good equipment makes your job easier and you ultimately save time. Keep the equipment properly calibrated and take all steps to maintain the instrumentation. As energy continues to become extraordinarily expensive we must take steps to conserve it; our very manufacturing existence might depend on it.
Performing a Leak Survey
The success of a leak survey requires three major elements: knowledge, planning, and follow-through. The knowledge component includes an understanding of the compressed air system, including all the subsystems and components. What are the sizes, types, and ages of the compressors? Have they been properly maintained? What about your traps and drains? Are your pressure gauges working? And, if so, is there adequate pressure for the various areas of use? What are the assigned pressures for these areas? Are there compressed-air applications that can be replaced by alternative, less energy-intensive methods? For example, instead of using compressed air for cooling, drying, or cleanup, try using low-pressure blowers or fans.
Knowledge can also include understanding your ultrasound instrument, how it works, and the techniques of inspection. If you are not too sure about the technology or how to use the instrument, there are training courses available that can help make you and other inspectors in your facility more competent and effective in your inspections.
Planning includes such elements as a map of the compressed gas system and its various components. If none exists, try taking digital photographs of each section using long-range and close-up views and labeling them. Planning also includes scheduling the survey. Don't try to do it all at once. Break it up so that the survey can be performed without negatively affecting the other maintenance responsibilities of the personnel assigned to the leak survey team.
Before the survey begins, have the inspectors walk through the various sections to review their route. The walk-through can help in a number of ways: it can identify potential safety issues, note any changes needed to the planned route, identify obvious leaks, and pinpoint what equipment to bring along such as flashlights, keys, or specialized leak inspection attachments.
Another important part of planning includes a leak tag/identification method. Once a leak has been located, it should be tagged (Figures 1 and 2). The tag number can be used along with a photograph of the leak in your report. The identification process is extremely important. The leak rate can be assigned to the leak in a report to demonstrate the cost savings and potential environmental impact associated with the leak. In addition, it can be used to be sure a leak is repaired.
 Figure 1. Nitrogen leak at union connection to control valve (orange tag in center of image) |
 Figure 2. Threaded connection leaks on the lines to the Finn tube radiation unit of a nitrogen system (orange tags) |
If a leak is not repaired all the effort and cost of the survey will be wasted. Therefore it is important to use a follow-up method to ensure that all identified leaks are repaired. In addition, when a leak has been reported as fixed, the repair should be checked. Sometimes the repair might cause another leak to manifest and sometimes the wrong component is repaired. Follow-through includes review of the survey, cost analysis, and, when possible, environmental impact analysis. A report can then be generated to demonstrate the effectiveness of the survey and the related cost-saving benefits.
Follow-through includes leak management. A survey typically identifies many leaks. The sheer volume of these leaks can seem overwhelming to a maintenance department that is already working hard to meet their assigned daily maintenance requirements. Therefore, it is important to implement a system that will allow for the leaks to be repaired on a workable schedule. One method is to prioritize the leak repair so that the most costly leaks or those that can affect production are repaired first, the next most important later, and so on.
Record keeping is another important part of post-survey follow-through. Some companies provide software that can help. One such freeware program is offered by UE Systems Inc. It is a two-stage software program that combines data management and comprehensive compressed-gas survey analysis. Users can review annualized and monthly data that includes leak cost and greenhouse-gas savings.
Conclusion
As we've discussed, compressed gases can be costly in ways beyond the obvious. The cost of producing or purchasing the gas is one factor. Safety, the environment, and equipment degradation caused by leaks and equipment inefficiencies can all affect a company's ability to compete and to maintain profitability. A planned, comprehensive leak survey program can provide savings to improve plant-wide productivity and profitability.