Easy to use testing techniques by operators are useful for troubleshooting equipment

L. (TEX) LEUGNER

Monitoring equipment condition has been around since the creation of the wheel. The wheel squeaked, the wheel hub began to burn, and we learned to grease the wheel with tallow. As the application of the tallow became more precise, the time between wheel failure was extended.

In turn, the development of troubleshooting using the senses of sound, sight, touch, and smell. However sensory perceptions have the disadvantage of being subjective and imprecise, over the years, condition monitoring technologies have been developed for industrial equipment.

In his book, Reliability Centered Maintenance , John Moubray describes 96 techniques to monitor the operating condition of equipment. These range from sensor y techniques to the application of highly sophisticated technologies such as fast Fourier transform (FFT) analyser, to determine the causes of vibration frequencies in rotating equipment.

The use of testing techniques can only be justified if they demonstrate a clear economic benefit. Substantial evidence exists that the intelligent use of even simple testing techniques will provide huge benefits to industry including:

1 Elimination or reduction of catastrophic machine failures and secondary damage where a failure has occurred.

2. Reduction in maintenance costs by avoiding repairs.

3. Reduction in downtime by reducing the scope of repair.

4. Increase in production by scheduling repair when convenient to operations.

5. Reduction in downtime and costs by having advanced warning, permitting effective planning, and scheduling.

6. Reduction in r isk to equipment and personnel from a safety perspective.

7. Revised insurance costs.

8. Elimination of ineffective or unnecessary preventive maintenance tasks.

9. Extension of time-based intervals of necessary preventive maintenance tasks.

10.Improvement in reliability, productivity, and efficiency of machinery.

Operators often know more about the equipment they operate than do maintenance personnel and can be trained to monitor equipment condition. Effective testing applied by operators must be gathered when equipment is at operating temperature and taken at the same point on the machine component when the data is collected.

The following testing techniques are common, easily applied, and only require that operations personnel have a sound knowledge of their equipment’s operation.

Q | Do the applicable equipment operators understand how contaminants enter a lubricated system?

LOGIC: Contamination of machine systems occurs in four ways, generated by the system itself (by nor mal wear, poor system or component design, surface fatigue and temperature related chemical reactions), implanted (by welding slag), induced (by careless maintenance practises), and escaped contamination (that enters a lubricated system through poor quality filters or poor filtration system design).

An operator’s simple contamination test is to obtain an oil sample in a glass jar allowed to sit overnight. When the jar is turned over, any contaminant will remain visible on the bottom surface of the jar. A decision can be made for further laboratory testing.

Q | Do the equipment operators know how to determine if water is a problem in a machine system?

LOGIC: Water contamination in a lubricated component can be determined by placing a few drops of oil on a hot plate. If the oil drops crackle or sizzle, there is excessive water present.

Q | Do operators know how to determine how effective oil filters are?

LOGIC: Every time an oil filter is replaced, it should be cut open, the filter media spread on a bench; and using a good quality magnifying glass or microscope, contaminants and wear metals will be obvious. A magnet passed under the filter media will move all ferrous materials. If any machine damage is suspected, or the level of contaminant or wear metals have increased since the last filter inspection, a ferrographic analysis of an oil sample should be carried out.

Q | Do operators know if a machine’s operating temperature has increased beyond normal?

LOGIC: Operating temperatures of industrial equipment are often unknown or ignored until after a failure occurs. The first step is to ensure that operators know the operating temperatures of their equipment under normal conditions, record this standard in the operators log or maintenance files and train operators to monitor any change in that standard during the life of the equipment. a) Rolling element bear ings – 71ºC (160ºF). This is the temperature at which lubricating oil or grease begins to oxidize. b) Hydraulic systems – Bulk oil temperature at the exterior of the reservoir should not exceed 60ºC (140ºF). c) Gear drives – Operate best in a temperature range of 49ºC–60ºC (120ºF–140ºF). Remember that an operating temperature rise of 50ºC (90ºF), combined with an ambient temperature of 15.6ºC (60ºF) will result in a “total oil operating” temperature of about 66ºC (150ºF). d) Worm gears – Operate best at oil temperatures of about 60–65ºC (140–150ºF). Higher temperatures may promote pitting of the phosphor bronze gear and the use of polyglycol synthetic oil can reduce temperatures by up to 10ºC, and reduce gear pitting. e) V-belts – Should not operate at temperatures higher than 60ºC (140ºF) and should be covered with wire mesh shrouds to ensure air flow. f) Gas turbines – Oil temperatures should be in the range of 54ºC–71ºC (130ºF–160ºF). g) Electr ic motors – There are four classes of motor winding insulation, each with a corresponding maximum temperature rating.

Operators should be aware of the following component systems and corresponding maximum acceptable operating temperatures.

Q | Are your operators willing and prepared to learn to effectively use these tools?

LOGIC: Operators can be easily taught to use common methods of testing temperature conditions that include the use of various temperature probes such as the digital temperature indicator.

When measuring the temperature of any component, remember it is the housing temperature that is being recorded. The internal components, (motor windings, rolling bearings, or the lubricant in a reservoir or gear housing), will be about 20ºC higher than the recorded temperature.

At least annually, a thermographic analysis should be carried out to locate hot spots in electr ic motors and mechanical devices such as drive couplings, bearings, and gear drives. There is almost no limit to the uses for which infrared thermography may be used for monitoring temperature related problems by operators, and handheld devices such as the thermocam are available.

Q | Do operators recognize machinery vibrations in your plant?

LOGIC: Technically defined, vibration is the oscillation of an object about its position of rest and these oscillations (or cycles) in a given length of time are referred to as the frequency of vibration measured in cycles per minute (CPM), or cycles per second hertz (HZ).

The amplitude of vibration is measured in displacement (distance or movement), velocity (speed) and/or acceleration (force), of the source of the frequency. Every piece of equipment contains moving parts, each of which will vibrate at certain frequencies. These frequencies are governed or generated by the vibration sources and will vary across a wide range referred to as a spectrum.

Common vibrations are unbalance, misalignment, defective bearings, or mechanical looseness. Once operators are f amiliar with these fundamentals, they can determine most common vibrations by placing a washer or coin on a smooth machine surface. The coin will display the vibration with its own. Good luck with these testing techniques.

The temperatures listed for electric motors include combined ambient temperature and temperature rise. For every 10ºC increase in temperature above the listed rating, the service life of the motor is reduced by about 50 per cent.