The cost of a component is a poor measure of its operational importance. A modest item with a long lead time can interrupt a programme just as effectively as a major assembly.
Criticality reviews consider failure consequence, redundancy, repair options and the route to the rig. Storage conditions and preservation requirements also influence whether a spare will be serviceable when required.
Maintenance history should feed back into the stocking strategy. Recurring demand, changing lead times and equipment modifications can all change the appropriate holding.
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