How do you determine spare parts criticality?
Most companies don’t really understand criticality and see it as a single dimension issue.
But that is just not right.
One of the things that people ask me about most often is the issue of spare parts criticality.
It seems that criticality is often seen as a single dimension issue, that is, an item either is, or isn’t, critical. But I don’t think that is right. I think spare parts criticality is a multi-dimensional issue.
What do I mean by multi-dimensional? Not that criticality exists in some science fiction space-time continuum but rather that it has a number of characteristics that need to be considered before deciding what to hold in inventory.
First, is the item in question machine critical or operationally critical?
By machine critical I mean, will failure of the item stop the piece of equipment of which it is a part?
By operationally critical, I mean, will failure of the item stop production?
These two characteristics are quiet different and have a different impact on what to do next.
For example, the globe in a headlight on my car is machine critical to the light. Obviously, the light will not work without the globe. But my car will still operate. In fact, in daylight hours there is no noticeable difference. If the globe fails at night I would notice the difference but would still be able to operate the car until I can get the globe replaced. Yes, safety will be slightly reduced but I think that this is, in this specific case, acceptable for a short period.
Compare the globe failure with a fan belt failure.
If you break a fan belt you won’t be able to drive for more than a few minutes before the vehicle starts to overheat and be un-drivable.
The fan belt is not only machine critical it is also operationally critical.
Yet, how many people carry spare fan belts for their cars? Not many.
Why: because the failure is rare and the result may be inconvenient but in most cases tolerable (catch a taxi, get the car towed, call the auto club etc.).
If you live in a city you are unlikely to carry a fan belt.
If you live in or are driving through a remote area you probably would carry a fan belt. The decision (and quantity to hold) is dependent upon the situation.
What about brakes. Everyone would agree that brakes are pretty important but who carries spare brake pads? No-one.
Why: because inspections will identify pad wear so that you replace the pads before they become dangerous (plus the occasional grinding noise is a bit of a giveaway!)
Everyone would argue that brake pads are operationally critical, but no-one would carry brake pads.
Here we have three items. Each is machine critical, two are operationally critical, yet none are carried as spares, except in specific (for most of us unusual) circumstance.
Spare parts criticality is definitely multi-dimensional and the inventory that we hold should be a function of the situation.
For some critical spare parts we can still operate until we get the spare, for some we can wait until the spare arrives, for some we can manage through condition monitoring.
Of course there are some items that we just can’t live without. Just don’t think that all items identified as critical will fall into that final category.
Our Spare Parts Criticality Assessment Tool can help you assess whether a specific spare part is critical to your operations and should be held in inventory.
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Posted by: Phillip Slater