Optimizing Equipment Replacement Schedules for Cost and Safety Efficiency

The typical battery for a car, truck, or service van has a three-year life expectancy regardless of the mileage or maintenance. Most batteries have a “date of installation” marking on them for this reason. As that date approaches, the smart car owner starts looking for battery sales. After that date, the smart car owner conducts regular battery testing until there is a sale or simply replaces the battery just before cold weather sets in or before heading off on a long car trip.

With your tires, it’s a similar thing; that life expectancy is five years, regardless of the mileage or maintenance. Or the amount of tread on it. The battery issue is a reliability consideration; the tire issue is a safety concern.

The life expectancies of specific electrical infrastructure components are published. A planned shutdown to replace them as those expected end-of-life dates approach is more cost-effective than simply letting them fail. For example, after 30 years of service (or whatever the manufacturer recommends) your dry-type transformers are ready for replacement. In an office building that uses fluorescent lighting, completely relamping on a set schedule (e.g., five years or whatever the manufacturer recommends) is far more cost-effective than playing a game of whack-a-mole as they begin to fail one by one.

Circuit breakers are expected to last 25 to 40 years, depending upon the type of breaker, type of service, and some other factors; go with the manufacturer’s recommendations. Remember that when a breaker fails, there is often no outward indication. One job of the breaker is to break the circuit upon overload, if the circuit is drawing 55A and the 50A breaker doesn’t open it would appear there’s no problem with the breaker. But breaker testing would show otherwise. If you start encountering bad breakers and they are all near their published end of life, the most cost-effective solution is to schedule a shutdown to replace all of them. However, this is a major capital investment and a hard sell to those who approve such outlays.

Don’t take the published figures or manufacturer’s recommendations as lower limits. They are “normal case” estimates. Consider car tires again. If you drive at high speeds, the lifespan of the tires will be significantly reduced. Improper inflation (over or under), hard braking, hard cornering, parking outside (exposure to UV), alignment issues, and other factors reduce the effective lifespan of the tire. It’s not just the amount of tread; it’s other things such as the ability of the sidewalls to do their job. If high-speed driving has caused the plies to start to separate, you won’t see that from the outside of the tire.

Similarly, if a motor is subjected to repeated short-cycle starting you will not see that from the outside of the motor. Some other factors that shorten the published life expectancy (which is typically 15 to 25 years, although we must note that some motors installed when the Panama Canal was built are still operating):

• Voltage imbalance
• Low power factor at the motor
• Excessive 3^rd and 5^th harmonics
• Improper lubrication (too much, too little, dirty injected through fitting, incompatible grease)
• Inadequate ventilation
• Misalignment
• Defects in the motor pedestal and/or base
• Voltage sags
• Voltage spikes
• Inadequate lubrication of gearbox
• Improper bonding or lack of bonding (a ground rod driven near the motor is a red flag for this)
• Moisture accumulation in the motor windings

The list can go on, but the point is that many things can result in a failure before a given piece of equipment reaches its life expectancy. It may be tempting to think that excellent maintenance extends that life expectancy, but the reality is that things can last only so long no matter how well you take care of them.

So what does this mean in real terms? Each piece of equipment has (or should have) an asset number. In your CMMS, note the published life expectancy for that particular asset. Then also note any reduction factors (with date of discovery, degree of severity, and estimated duration) and estimate a modification multiplier. For example, it turns out that the motor with asset number B75892 has had 7% voltage imbalance since it was installed ten years ago. You give its 20-year life expectancy a multiplier of 80%, which would mean scheduling a replacement for six years hence.

Do you start with the most critical production equipment? No, you start with the PPE. Fall protection harnesses, for example, should be replaced at age 10 if they have never been used. Sooner if they have. Why do you start here? Because the order of priority is:

1. Safety
2. People
3. Production

And under production, the production department should prioritize each major asset (e.g., production line). They will account for factors such as the revenue produced and the orders committed. While generally the major asset prioritization is stable (e.g., Line 3 is more crucial than Line 5), the situation can become fluid and the priorities can suddenly change.

For example, a new customer with high potential is having a test run produced on a minor machine that formerly was way down the list. The production superintendant will want to ensure that machine is reliably producing with a low defect rate. If you do the age assessment on that machine’s components, you may find some are due for replacement. Maybe they will last until this crucial run has completed. But rather than count on good luck, prepare for bad luck. Share your findings with the production superintendant or the plant manager and try to line up replacements now so that you can avoid playing the lead time waiting game after a failure.