Missing data is a common problem in reliability calculations. Ideally, you want to know both the ‘birth’ and failure dates of the item so that the lifetime is known. The failure date is straightforward since it can be derived directly from the work order data. For subsequent failures, the previous failure date can be used as the birth date. The birth date is not so obvious however at the initial start of the calculations. In the ideal world, your plant is brand new when you start the reliability calculations. Unfortunately, this does not happen very often, most plants have been operational before they commence utilization of an EAM application. So, what if the first history records are recorded for an asset in 2010, the year you started using the EAM application, but the asset was originally commissioned in 2000. Do you assume that no failures have occurred in the 10-year lifespan of the asset? That would be unrealistic. Having no other data than history starting at 2010, you have two options:
-
Start calculating from 2010, assuming all assets and parts were in ‘top condition’, in essence replacing the commission date of the assets with a date equivalent to the system launch.
-
Be more conservative, wait for the first failure, and use that as the base for your future calculations. Essentially this involves ignoring that first event and only using it as a surrogate commission date.
An installation parameter will be available to control this process.