Three levels of condition-based maintenance

Even in today’s high-tech world, many companies still have a limited view of their compressed air system health, and often take a “better safe than sorry” approach, and prematurely replace components. This focus on routine or recommended compressor maintenance often needlessly costs compressed air users thousands in added maintenance expense. 

However, a shift is occurring in maintenance of equipment and systems called prognostics and health management. Although it uses similar predictive maintenance (PdM) diagnostic tools such as infrared, vibration monitoring, and oil analysis to deliver the current condition of components, it differs in that it does not correlate and trend the measured parameters. Prognostics is a scientific discipline which delivers remaining useful life through modeling of a statistically significant sample of systems. The algorithms used in prognostics focus on assessing how far the component has degraded beyond “day one” health, and at what point the component will no longer perform its intended function.

When it comes to prognostics in compressed air systems, knowing what parameters should be measured and how they should be analyzed help to form good practices in condition-based maintenance (CBM). 

Comprehensive system insights 

Fluid and vibration levels, noise, and air temperature are good parameters to assess the health of a compressed air system. While compressor controllers and performance indicators can provide certain readings, facilities often lack comprehensive knowledge and insight about their equipment, and the knowledge about how the different parts of a compressed air system relate to one another. A real-time snapshot of equipment isn’t enough—plants need a way to predict the future of their equipment. 

A CBM system ensures that all components of a system are running efficiently and helps operators predict issues that may occur down the road. This type of monitoring uses unique algorithms that calculate and predict service intervals based on the actual maintenance needs of equipment, not just an industry average. 

There are three main tiers of CBM. Each of the three have interdependencies and provide facility managers with insight so they can make informed, educated decisions based on facts about their equipment.

1. Lubricant CBM. Monitoring the lubricant through sampling and lab testing determines contaminant and fluid integrity levels as well as metal content in the fluid. Determining the health of the oil allows for change-out at the right time. Changing too early creates needless expense and changing too late shortens the life of the compression element, called the airend. 

The health of the oil is an indicator of the health of the compressor, much like a blood test for a person. Additionally, signs of wear and aging of the airend can be determined through the metal content in the oil. For example, high levels of metal in the lubricant may indicate that the rotors or bearings are wearing down, depending on the type of metal circulating in the lubricant. Another source of metal could be heat exchangers or other passages with which the oil contacts. The metal content in the lubricant, therefore, also informs the mechanical CBM tier.

2. Mechanical CBM. In addition to lubricant CBM, shock pulse monitoring examines the vibration and noise levels to provide a comprehensive view of the airend health. This typically involves special instruments and sensors. 

High noise or vibration levels can indicate issues such as bearing wear or rotor degradation. Trending of the wear through vibration monitoring with detection of metals in the oil allow for correlations and predictive models to be built for remaining useful life. 

3. Pneumatic CBM. This type of monitoring takes a deep look into the air quality to make sure that the entire system is working efficiently. With CBM, plants can make better decisions based on facts about their unique systems. Using systems such as Ingersoll Rand Air System Modeling and Simulation (ASMS), plants can understand their specific compressed air systems better. This level of monitoring tests the compressed air within the system, air pressure in the piping, air flow levels, humidity, and more. These systems also can indicate where the system needs another piece of equipment. For example, if a test shows that there is high humidity in the air, it indicates that the system may need dryer technology to dry the air before it exits the system. 

The Industrial Internet of Things (IIoT) is at the forefront of the manufacturing industry and connected data and monitoring can help facilities find potential issues sooner than basic methods, saving time and resources. Connected compressed air systems can help manufacturing facilities improve overall efficiency by allowing them to virtually monitor their systems and PdM needs down the road. 

Additionally, some compressor controllers and maintenance cloud systems use advanced algorithms and parallel processors to enable operators to get the lowest energy consumption and best performance out of their compressed air systems. 

With a total system approach to CBM, facilities can improve efficiency by monitoring and storing data in the cloud to see how all of the air system components work together. Visibility into the interaction between the system components helps to predict exact maintenance intervals—there’s no guessing involved. 

From consumables to key parts like rotors, all the way to the end at the point-of-use, digital connectivity provides operators insight into every step of the process. This level of monitoring, through system design and diagnostics, enables plants to maintain higher levels of reliability, often called reliability centered maintenance. 

Tianshu Zhang is services product manager for Ingersoll Rand Compression Technologies and Services.