Predictive Maintenance

Predictive maintenance is the monitoring of equipment operating conditions to detect any signs of wear that is leading to a failure of a component. The goal of the predictive maintenance program is to track the component wear with a methodology that insures that any impending failure is detected. Once detected, the component wear is tracked more closely. The component will then be scheduled for replacement before it fails during a scheduled run.

Monitoring the operating condition of the equipment can be accomplished by examining its operating dynamics. The most common techniques for measuring operating dynamics include:

Vibration analysis

Thermography

Ultrasonics

Oil analysis

Lubricant condition

Wear particles

Vibration analysis measures the physical operating vibrations of rotating equipment. Based on the type of equipment, the analysis can indicate problems with bearings, belts, chains, gears, shaft misalignment, and out-of-balance conditions. The major impact that vibration monitoring has in most plants is its use in detecting bearing problems. By knowing days, weeks, or even months in advance that a component is wearing and will fail, the maintenance department can change the part with minimal impact on the operations department.

Thermography measures the temperature of a component. This trending of temperature indicates wear because increased wear is generally accompanied by a temperature rise. The thermographic equipment can be anything from a

small temperature strip to an infrared imaging system. The level of detail, coupled with the ability to measure the parameter safely, quickly, and accurately, determines the cost of the tool required. Thermography is typically utilized for finding potential problems (usually poor connections) with electrical and electronic systems. However, it is also used in high temperature applications like furnaces and heat exchangers. In addition, it is used to indicate misalignment in drive couplings.

Ultrasonic inspections are used to check for high frequency noise that is typically created by leaks. Ultrasonic detectors can thus be used to find air leaks, steam leaks, and other fluid leaks. Using stationary detectors, ultrasonic detectors can also be used to inspect pressure vessels and other containers. Although ultrasonics tend to be used as an instantaneous check, the data, especially for pressure vessels, can be trended to show rate of wear.

Oil analysis can be used to refer to at least two different techniques. The first examines the lubricant itself for condition. The analysis reveals whether the oil has become contaminated, is losing its lubrication qualities (corrosion resistance, wear resistance, load rating, etc.), or has been damaged from overheating. The second examines wear particles in the lubricant. This is an indication of the type of wear occurring in the unit being lubricated. If the wear particles show an accelerated wear rate, then the unit can be more closely inspected to find the cause of the wear and correct it. This leads to extended life of the component by detecting a problem before any damage is done to the component.

Because each of the predictive techniques are used to check for a particular type of wear, a mix of the techniques is typically used in a predictive maintenance program. The predictive maintenance program focuses on the following steps:

Track equipment conditions not easily inspected in the preventive maintenance Program

Reduce the amount of effort in the preventive maintenance program by using technology instead of disassembly

Reduce the spare parts required to be on hand for unexpected equipment breakdowns or component failures

Allow for a high level of planned and scheduled maintenance work, lowering the amount of conflict with the production schedule

Increase the equipment capacity by insuring it is technically capable of performing at design specifications

Some of the indicators that can be used to determine if the predictive maintenance program is successful follow.