Process Technical Services (PTS) can assist in setting up and managing a predictive maintenance program until the local maintenance organizations can take over the responsibility for the program. Predictive maintenance programs offer cost savings over routine or time-based preventive maintenance because tasks are performed only when warranted.
Predictive maintenance (PdM) techniques help determine the condition of in-service equipment in order to predict when maintenance should be performed.. Predictive maintenance programs measure equipment on a regular basis, track the measurements over time, and take corrective action when measurements are about to go outside the equipment operating limits. Repairing equipment as needed using predictive maintenance requires fewer man-hours and parts than preventive maintenance. However, tracking the measurements requires new tools, training, and software to collect and analyze the data and predict repair cycles.
PdM or condition based maintenance attempts to evaluate the condition of equipment by performing periodic or continuous (on-line) equipment monitoring. The ultimate goal of PdM is to perform maintenance at a scheduled point in time when the maintenance activity is most cost effective and before the equipment fails. This is in contrast to time and/or operation count based maintenance where a piece of equipment gets maintained whether it needs it or not. Time based maintenance is labor intensive, ineffective in identifying problems that develop between scheduled inspections, and is not cost effective.
The "predictive" component of the term "predictive maintenance" stems from the goal of predicting the future trend of the equipment's condition. This approach uses principles of statistical process control to determine at what point in the future maintenance activities will be appropriate.
Most PdM inspections are performed while equipment is in service, thereby minimizing disruption of normal system operations. Adoption of PdM in the maintenance of equipment can result in substantial cost savings and higher system reliability.
To evaluate equipment condition predictive maintenance utilizes nondestructive testing, technologies such as infrared, acoustic (partial discharge and airborne ultrasonic), corona detection, vibration analysis, sound level measurements, oil analysis and other specific online tests. Vibration analysis is most productive on high speed rotating equipment and can be the most expensive part of a PdM program to get up and running.
Acoustical analysis can be done on a sonic or ultrasonic level. Sonic monitoring equipment is less expensive, but it also has less uses than ultrasonic technologies. Sonic technology is useful only on mechanical equipment while ultrasonic equipment can detect electrical problems and is more flexible and reliable in detecting mechanical problems.
Oil analysis is a long term program that, where relevant, eventually can be more predictive than any of the other technologies. It will take years for a plant's oil program to reach this level of sophistication and effectiveness.
Infrared monitoring and analysis has the widest range of application from high to low speed equipment and it can be effective for spotting both mechanical and electrical failures. Some consider it to be currently the most cost effective technology.
Most facilities practicing predictive maintenance purchase or develop a specialized database, commonly referred to as an asset management system (AMS) or a computer managed maintenance system (CMMS). To track trends, a database system should be able to store:
- List of critical equipment
- Maintenance and measurement procedures for each type of equipment
- Maintenance schedule
- History for each measurement
- Limits for each measurement (maintenance alarm trigger)
Many systems also track warranty status, depreciation records, and purchasing information and can generate works orders, manage schedules, and track employee training histories and related skills.
Unplanned downtime cost variables are:
- Lost revenue during downtime, especially critical if the plant is running at or near capacity, or in highly competitive markets. This measurement is in dollars per hour.
- Lost revenue due to loss of customer confidence-how many customers will leave you.
- Replacement cost of damaged electrical or production equipment.
- Repair costs, especially labor.
- Cost of scrap.
- Cost to clean and restart production.
- Insurance premium reductions.
Process Technical Services personnel are experienced in designing and implementing predictive maintenance programs. This involves writing the procedures and training plant maintenance personnel and management how best to utilize and maintain the program for the life of the plant. A disciplined predictive maintenance program can produce substantial benefits in terms of reduced maintenance costs and avoided lost production.