Preventive maintenance is a schedule of planned maintenance actions aimed at the prevention of breakdowns and failures. The primary goal of preventive maintenance is to prevent the failure of equipment before it actually occurs. It is designed to preserve and enhance equipment reliability by replacing worn components before they actually fail. Preventive maintenance activities include equipment checks, partial or complete overhauls at specified periods, oil changes, lubrication and so on. In addition, workers can record equipment deterioration so they know to replace or repair worn parts before they cause system failure. Recent technological advances in tools for inspection and diagnosis have enabled even more accurate and effective equipment maintenance. The ideal preventive maintenance program would prevent all equipment failure before it occurs.
condition montoring
conditon montoring is monitoring the vibration of rotating machinery in an attempt to detect incipient problems and to prevent catastrophic failure. Some asset failures have expensive and far-reaching consequences. These failures can shut down entire production line, The more common version of this new maintenance strategy, condition monitoting maintenance, is also based on the statistical pattern of failure exhibited by equipment. Many common failure modes are presaged by changes in equipment behavior, and monitoring these parameters can provide early warning of failure or degradation. Under condition monitoring maintenance, these parameters are monitored periodically, usually based on manually collected data.maintenance is often based on analysis of bearing heat signature, lubricant condition, and rotating equipment vibration To others, it is monitoring the infrared image of electrical switchgears, motors, and other electrical equipment to detect developing problems. Instead of relying on industrial or in-plant average-life statistics (i.e., MTTF) to schedule maintenance activities The common premise of condition montoring maintenance is that regular monitoring of the mechanical condition of machine-trains will ensure the maximum interval between repair and minimize the number and cost of unscheduled outages created by machine-train failures. Condition monitiroring is much more. It is the means of improving productivity, product quality, and overall effectiveness of our manufacturing and production plants.
There are five nondestructive techniques normally used for predictive maintenance
management:
(1) vibration monitoring.
(2) process parameter monitoring.
(3) thermography.
(4) tribology,Ultrasound and Oil Analysis
(5) visual inspection.
Each technique has a unique data set that will assist the maintenance manager in determining the actual need for maintenance.
Vibration monitoring.( Vibration Analysis)
Vibration Analysis Techniques are the interpretation of aquired vibration analysis data, The frequency of the vibrations can also be mapped since certain frequencies will only be present when conditions that indicate an impending defect are present to determine the cause of specific machinery defects. In order to identify the condition of a machine, vibration readings are taken in different measurement points. Typically the measurement points are choosen at the bearing positions. Bearings are the closest point to measure the dynamic vibration coming from the rotor and are also vital for good operation of the machine.
The assets could benefit from Vibration Analysis:
• Rotating equipment such as motors, pumps, blowers, fans, gear boxes, mills, rollers, crushers, compressors and turbines
• Interconnected structures, static equipment and piping.
the equipment problems can Vibration Analysis detect:
• unbalance
• misalignment
• looseness
• bent shaft
• gear problems
• bearing problems
• motor internal faults
• electrical grounding faults
• noise excitation (piping/structural
Thermography
(http://support.fluke.com/find-sales/download/asset/2519626_a_w.pdf)
Infrared thermography Cameras work on the principle of converting infrared energy signals radiating from all the surface of all objects into heat / temperature information and using the same to have extensive knowledge of behavior of the objects . The following are some of the incredible applications we found in clients' workplaces. In a fertilizer factory, we used infrared thermographycamera to scan the end portion of a heat exchanger which had number of passes inside. Their problem was to find out the reasons for poor thermal efficiency they were facing lately. Presto! our scanning identified passing leaks from one pass to another which was clearly seen in the thermal profile and subsequent digital thermography pictures. The company could save much money from an accurate prediction of their problems. some of the drum drivers are located in inaccessible places and can't be reached easil the infrared themography camera from the ground level to check the heating of their bearings. This way it is possible to locate faulty bearing points long before they become dangerously hot which can cause breakdown
Aplication
Conditions Detected
Drives/Conveyors, Pillow Blocks, Couplings, Gears, Power Transmission Belts, Pulleys, Shafts.
Overheated bearings or rollers, misalignment of shaft, pulley or coupling, lubrication failure uneven pressure.
Motors
Overheating of windings and bearings, blockages in cooling passages, friction, damping, material deformations, brush contact problems, rotors
Pumps/Compressors/Fans/Blowers
Overheated bearings, high compressor discharges temperature, high oil temperature, and broken or defective valve.
Internal Combustion Engines
Valve or injector malfunction, blocked radiator tubes and oil coolers. Thermal distribution, high radiator inlet or outlet temperature.
Heavy Duty Equipment - Tires, Bearings, Brakes, Hydraulics, Kilns, Ball Mills, Paper Machines
Overheating brakes, tires, bearings, pulleys, gears, gear or pulley misalignment, and blockages in hydraulics.
Mechanical DriveTurbines and Small TurbineGenerator Units, Gas Turbine, Exhaust Ducts
High lube oil temperature, high bearing temperatures, faulty stop/control valve operation, uneven metal temperature, leaking shaft seals, gas turbine firing conditions, including deterioration in firing chambers, cross firing tubes.
Ovens, Furnaces, Kilns, Pipes
Location and severity of damaged insulation, location of steam leaks in buried steam lines.
Valves: Shutoff Valves, Relief valves, steam traps
Leakage, Blockage.
Hot connections on the Motor Control Center.
The benefits of implementing condition monitoring
systems to optimize total plant operation. A comprehensive condition monitoring maintenance management program utilizes a combination of the most cost-effective
tools-that is, vibration monitoring, thermography, tribology, etc.-to obtain
the actual operating condition of critical plant systems, and based on these actual
data, schedules all maintenance activities on an as-needed basis. Including
predictive maintenance in a comprehensive maintenance management program
will provide the ability to optimize the availability of process machinery and
greatly reduce the cost of maintenance. It will also provide the means to improve
product quality, productivity, and profitability of our manufacturing and
production plants. Avoid health and safety and environmental risks. , reduce downtime, extend asset life, reduce overhauls,
Maximum Utilization of Maintenance Resources.The maintenance organization controls a substantial part of the total operatingbudget in most plants. In addition to an appreciable percentage of the total plant labor budget, the maintenance manager, in many cases, controls the spare partsinventory, authorizes the use of outside contract labor, and requisitions millionsof dollars in repair parts or replacement equipment. Therefore, one goal of the maintenance organization should be the effective use of these resources. Forecasting failure mode and estimating time until failure; conveniently schedule targeted proactive failure interventions and prevent loss of production availability/productioncapacity/product quality
Optimum Equipment Life
One way to reduce maintenance cost is to extend the useful life of plant equipment.
The maintenance organization should implement programs that will increase the useful life of all plant assets.
Minimum Spares Inventory
Reductions in spares inventory should be a major objective of the maintenance
organization. However, the reduction cannot impair their ability to meet goals
1 through 4. With the predictive maintenance technologies that are available
today, maintenance can anticipate the need for specific equipment or parts far
enough in advance to purchase them on an as-needed basis.
Ability to React Quickly
Not all catastrophic failures can be avoided. Therefore the maintenance organization
must maintain the ability to react quickly to the unexpected failure. Improve reliability (mean time to repair, mean time between failure, plantavailability and utilization)
VIBRATION FREQUENCIES AND LIKELY CAUSES.
Frequency in terms of RPM
Most likely causes
Other possible causes and remarks
1X RPM
Unbalance
1.Eccentric journals, gears or pulleys.
2.Misalignment or bent shaft-if high axial vibration.
3.Bad belts if RPM of belt.
4.Resonance.
5.Reciprocating forces
6.Electrical problems.
2Xrpm
Mechanical Looseness
1.Mis alignment if high axial vibrations.
2.Reciprocating forces.
3.resonance.
4.Bad belts if 2x RPM of belt.
3Xrpm
Misalignment
Usually a combination of misalignment and excessive axial clearances(looseness)
Less than 1XRPM
Oil whirl(less than ½ rpm)
Bad Gears
Aerodynamic Forces
Hydraulic forces
Mechanical Looseness
1.Bad drive belts.
2.back ground vibration.
3.Sub harmonic resonance.
Many times RPM(Harmonically
Related frequency)
Gear teeth times RPM of bad gear
Number fan blade times RPM
Number of impeller vanes time RPM
May occur at 2,3,4 and sometimes higher harmonics if severe looseness
