Spare Parts Classification

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The definition of Spare Parts Classification can fluctuate depending on the vision and/or focus assumed at any given moment. Some examples of definitions:

  • Part criticality
  • Parts grouping or commodity
  • Part Type

At IDCON INC we have a definition of part classification as follow:

What type of spare is it when it sits on the shelves?
Does it influence the plant performance?
Is it hard to find?

Looking at it in this perspective, we have classified spare parts as follow:

  • Critical – We can’t live (or sleep) without it.
  • Insurance – Yes, let’s have it in case of…
  • Low Risk – No problem (I can still sleep) if we need it now
  • Non-Stock – We will pick it up tomorrow

In order to define a part with these classifications, asking simple questions can give us a type of approach that can be objective. They are usually answered by a skilled craftsperson, supervisor, store room attendant, craft leads or reliability engineer (sorry, purchasing agents usually are not the best resource).

In an existing inventory, we will have the parts transaction data (good issues, parts used) available that will support us in this effort. When new equipment is purchased, these questions can be supplied to the equipment manufacturer (NOT vendor) for their input (I strongly suggest a review by the plant).

The following is a list of the questions:

Item or Question Definition Comments
Predictability of failure Consistent repetition of failure, making it possible to know in advance that it is going to fail
  • We have, or can estimate the part’s Failure Developing Period sometimes identified by manufacturer
  • It will fail based on existing performance or MTBF (Mean Time Between Failure)


Probability of Failure A strong likelihood or chance (Risk?) of something.
  • Will it fail?
  • We have data, or can estimate, X running hours. Sometimes given by the manufacturer.
  • It will fail based on existing performance or MTBF
Time from failure to “real” production loss From the time it fails to when production STOPS or product quality is affected  Things to consider:

  • Complete plant is down
  • Specific product line is down, market demand can be met by other means
  • Equipment start-up will be impacted (time dependent)
  • Is it a unique or are their redundant equipment
Consequences of not having the part when needed The effect, result, or outcome of something occurring
  • What will happen to Production throughout?
  • Will it affect safety and the environment?
  • Will it affect product quality?
Disassemble time (before installing the part) Time needed to take apart an assembly or section in order to reach and change the part
  •  Time required getting and changing the part.
Part preparation time Time needed to get the part ready
  •  An example is a motor that has been in storage for X amount of years. There is a preparation time needed before installation.
Can we repair and return to inventory Yes or No
  • Mechanical seals, motors, gearbox
  • Repair can be done in-house or by an outside contractor
Availability of substitutes or replacements Are parts available that can substitute or replace WITHOUT modifications or specs. Change?
  • No Substitutes – Cutting die of with specific dimensions, hardness, cutting angle and/or brackets<
  • Like for Like – Third party vendor that can provide a like for like cutting die.
  • Like for Like – Manufacturer that can provide an air filtration unit with the same specifications.
  • Generic – Bearing 62014 ZZ, Fuse 1 Amp


In our next tip, we will look at assigning values to these questions and making some sense into the Spare Part classification process.

Torbjörn Idhammar

Torbjörn Idhammar

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