Good spare parts management is much more complicated than many people believe. It’s not a matter of having a spare for every contingency. In fact, such a strategy can easily increase rather than decrease downtime.
First, consider the fact there is only so much space in a given facility. If you had a widget factory and 100% of its space could be used for making widgets, that would be ideal. But it is unattainable. That space must include employee lavatories, break rooms, administrative offices, places for the infrastructure (electrical service and power distribution, water and sewer, plant air), shipping and receiving, packaging, quality control stations, meeting rooms, raw materials, components, and so on. And, of course, the maintenance shop.
Somewhere in what is left must be shoe-horned in a spare parts room or similar area. Just as with those other uses, spare parts space allocation comes at the cost of the space available for making those widgets.
An analogy is this: Let’s say you have a 2,000-sq-ft home. After accounting for space taken up by closets, bathrooms, bedrooms, kitchen counters, the HVAC system, etc., you have 800 sq ft for entertaining guests and engaging in other activities in this living space. But you’ve read so many useful articles that you can’t bear to toss out your magazines. So, you stack them up in case you need one of those articles again.
After a couple of decades, they eat up half your living space. But you are prepared in case a situation comes up because you have an article to cover it! Think how much the mortgage is and how little use you are getting compared to a non-collector with a much smaller home.
One problem that arises is if you need that article, you might waste many hours trying to find it. This also is a problem with spare parts inventory. How do you catalog and locate all that stuff? And how do you decide which inventory is critical enough to track and maintain versus inventory that is just clutter kept for a statistically insignificant risk of needing it someday?
Another problem: paper deteriorates over time. And so do many kinds of spare parts. Now think of a 50HP motor bought as a spare when a new production machine was built and installed 20 years ago. Properly maintained motors that operate in a proper environment (low voltage imbalance, no thermal issues, proper bonding, etc.) typically last for many decades. But one stuck on a shelf will deteriorate as, over time, it missed the preventive maintenance it needed if it had been installed.
When you go to get that spare motor, you discover the shaft won’t turn. It’s warped due to how the motor was stored. Also, the motor case is corroded, despite being stored indoors. And hardened dust has totally clogged the vents.
For critical equipment, a way to prevent the “gone bad in storage” problem is to determine the anticipated useful life of the motors, transformers, etc., and simply replace them when the clock runs out. There are, in fact, tables published with this information.
Standardization
One way to reduce the spare parts count is to standardize. At a three-shift, multi-building plant in Tennessee, lighting systems had been installed as many different, unconnected projects. Consequently, there were dozens of different lamp models, with spares for each. The amount of space devoted was, as the plant engineer described it, “insane.” The plant engineer proposed replacing the older lighting systems such that they would use the most commonly used lamp (in this case, 277V fluorescent).
What was done instead was to get rid of the spares entirely and hire a relamping service. However, all future lighting projects were standardized. The standardization idea for other spare parts took hold, and within a year the storage requirements decreased by 40%. Another 30% was gained by eliminating spare motors and transformers, and the racks of EMT and rigid (plus the associated fittings), under the theory the plant was already built and such items should be ordered specifically for whatever projects required them.
This 70% reduction in materials storage space allowed relocating the spare parts operation right next to the maintenance department in a cage instead of in a big room. The former spare parts area was then used for two small additional production lines that brought in enough revenue to pay for several maintenance salaries.
The predictions of runaway downtime never came true. There were a few instances in which a motor had to be expedited from the local electrical distributor via special delivery. But there was never again an instance in which a stored motor failed only a few hours after being installed and its replacement had to be expedited from the local electrical distributor via special delivery. In other words, cleaning up the motor storage issues eliminated the middle step of saving the day with an on-hand spare only to need one delivered anyhow.
Does this mean you should never store spare motors? No, but if you do, you need to use maintenance resources to conduct preventive maintenance on those motors the same as if they were installed in the plant. Doing this for something you don’t use for 20 years is inefficient.
There’s no single right way or best way to manage the spare parts at all locations; each situation is different. Intelligent management of spare parts begins with accurately assessing what your situation is. A mentality of zero risk tolerance means poor utilization of all resources. So, a degree of acceptable risk must be established for each piece of equipment and its related spare parts.
Always keep in mind just how much production space and other resources you would be allocating to spare part your way out of downtime. In many cases, it’s not worth the cost.
