The Pragmatic Application Of The 'Parallel Non-Operating Redundancy' Formula In Practicing RCM

Given a mobile fleet which will have a number of equipment in it, this is how I use the 'Parallel Non-Operating Redundancy' Formula to determine the reliability or availability of the system.

Knowing that there are only two places to improve reliability (and eventually availability): at the system level and at the maintainable item level (i.e. equipment and component level). Having stated the place, the time for that is at the 'design stage'. That is why we say 'reliability is inherent in design'.

At the maintainable item level, that is the realm of the OEM (Original Equipment Manufacturer). At the system level, this is where the end user can influence greatly. Off course it is harder to do that at the Fixed Plant once the infrastructure is agreed with the end user, designed and installed. The mobile plant on the other hand, allows for greater ease and flexibility with 'redesigning' the system once a redundancy or standby is put in place because the assets are mobile and not permanently fixed in place.

In designing the system for the mobile plant I leverage the 'Parallel Non-Operating Redundancy' Formula which easily and logically accommodates standby configurations into determining the true inherent technical limit capacity of the fleet where you can then confidently 'balance capacity and demand' then put together your production plan confidently.

You can easily model this in MS Excel without the need for new softwares but like all modelling you must make some reasonable educated assumptions.

For example, if you were to have 38 trucks in a fleet and from 'Linear Programing' you have established that 33 is the optimum number to 'balance capacity and demand'.

Now allowing for planned and breakdown maintenance you might look at operating 24 trucks: nine (9) undergoing maintenance (either planned or breakdown); and five (5) on actual standby (either hot or cold).

As you improve your Maintenance Efficiency (speed - MTTR) and Maintenance Effectiveness (quality - MTBF), your actual number of trucks operating can go back up from 24 trucks but it will be between 33 and 24 and your optimum number of trucks required to be operating might be around 27 trucks as the 'sweet spot'.

Should other variables such as UoA, Operating Efficiencies and Operating Rates were to increase as determine by Mine Planning and Mine Operations, you can move this number of trucks operating higher depending on your budgeted tonnes to be moved. The buffer of additional truck numbers will allow you to park up trucks and move them in only when there is a surge in production demand or the mine plan shift to hauling over long distances and you want to maintain the planned cycle time which means you will have to now move the additional standby trucks into operation.

See this link below for this pragmatic case given as example above as modeled in MS Excel and leveraging the 'Parallel Non-Operating Redundancy' Formula.