Maintenance spare parts

Why devote an entire article to spare parts, and a relatively long one at that? That's the question the reader may be tempted to ask. Why devote so much space to such trivial things as screws, fuses or indicators, because that's the simplified view we sometimes have of spare parts. Yet we have all heard, at one time or another, of factories whose operations have been crippled by insufficient stocks of spare parts, or even which have broken down due to the absence of an essential spare part (a situation which is, alas, commonplace in many developing countries); we have also heard of the logistical problems of countries at war, seeking, sometimes with great difficulty, spare parts for their tanks, ships or aircraft. These trivial observations show that spare parts are apparently an important element in the smooth running of a production unit, but they don't explain why, nor do they provide the keys to analyzing the problem. We'll start by explaining why spare parts play an important role in maintenance, and then give an overview of the contents of this article.

To put it simply, any industrial "good" (or, more generally, any good produced by technology) is made up of component parts whose general characteristics (drawings, tolerances, materials used, various treatments, etc.) and interface specifications with neighbouring parts are precisely defined, and that compliance with this precise definition of each component is an imperative condition for the proper functioning of the whole; at least, that's how it should be. This philosophy of defining a good is therefore more or less incompatible with the idea of "repairing" a damaged or out-of-date part, because repair almost inevitably entails changes to these characteristics, and therefore risks of malfunction.

Maintaining equipment in satisfactory operating conditions - or, to put it another way, maintaining its "operational safety" - means that any component which no longer complies with its specifications, whether as a result of an accident, wear and tear caused by operation, or because age has altered its characteristics (as in the case of rubber parts), must be replaced by a new element, or at the very least reconditioned in such a way as to restore all its initial characteristics. It must be stressed that the identity of the replacement part to the initial component is not limited to its geometry, but includes all its characteristics: a mechanical part must be geometrically identical to the design drawing, but this identity will also include the material used, the heat treatments it undergoes, the surface finish, etc. In some cases, this perfect identity is a vital requirement (screws used in the structure of an aircraft, for example).

The user of the asset must therefore have a sufficient...