The Equipment Overhaul Paradigm
Overhauling equipment is expected to bring it to an “as good as new” state. But is this really the case in reality? Equipment will deteriorate over time and progressively lose its ability to function. No matter how extensive the overhaul, the equipment will unlikely be up to the level of “newness” as when it rolled out of the assembly line. Sure, if you have this vintage automobile from the 1930s, and spend an absolute fortune on its overhaul, it might come close to being new again. But somewhere in the structure of this automobile, there will an element that is “as good as old” and vulnerable to imminent failure. Also remember that this vintage automobile is not out there generating revenue. There is no accountant running after you with regards to budget constraints or revenue increases. Where there is passion, cost might not matter.
I used to have this discussion with seasoned maintenance engineers in the day. They would refer to this pump that came back from an overhaul as their pride and joy. It was shiny and ran smoothly. And expected to last as long as it had lasted before the last overhaul. And they did deserve a lot of credit as overhauling a pump is no easy feat in terms of logistics. The questions I used to ask them was:
- Are you sure its going to last as long as before you overhauled it?
- Was the cost of this overhaul worth it?
- Could in-situ maintenance be an alternative to an offsite overhaul?
As mentioned earlier, the overhaul of equipment does not make it as good as new. It might not be as good as old but somewhere in between. We refer to the renewal factor in Reliability Engineering. If the renewal factor is 50%, then the expected life after the overhaul will be around half of the previous life before the overhaul. The estimation of the renewal factor is easy once the asset is operating again. Also bear in mind; the overhauled equipment is shiny and new but the surrounding assets might not be. Those connections will influence the timing of failures. For example, if a pump is overhauled, the base it sits on might not be in good condition. Or, the piping connections might vibrate and so on. Therefore, the pump’s environment might lead to faster deterioration than expected.
Overhauling high capacity or complex equipment can be extremely costly. For example, to overhaul a large pump, it requires disassembly and shipping offsite. Often to a maintenance shop located in a remote location. Disassembly could involve removing the roof of the pump house requiring the use of cranes to lift the equipment out. Heavy haulers and specialized transport are also required. So, its not only about the cost of the overhaul itself but also all the work required to plan, disassemble, reinstall, and transport the equipment. Don’t forget any revenue loss incurred. This all adds up and its not uncommon to have overhauls costing in the hundreds of thousand dollars when completed.
The overhaul evaluation exercise
So how does life and cost element all come together to evaluate the need for an overhaul? Typically, we would use a cost optimization tool. The more frequently we overhaul, the higher the cost incurred. The less frequent the overhaul, the higher the risk of failures hence the increase in lost revenue and/or high unplanned repair costs. There is an optimal point combining cost, frequency and life characteristics which will indicate the optimal overhaul frequency. The graphical output related to the optimization exercise is highlighted in Diagram 1 below.
What if the overhaul frequency turns out to be an unrealistic number such as every 100 years? In this case, the optimization exercise is informing us that overhauls are not cost effective in the lifetime of the particular equipment considered.
Therefore, no matter how shiny the overhauled pump looks when recommissioned, it is important to assess the cost benefit related to the overhaul. Especially if it is expensive in terms of downtime, labor and cost. If the exercise excludes an overhaul, then consider other cost-effective alternatives such as
- In situ maintenance combined with advanced condition monitoring techniques
- Equipment replacement
- Run to failure but only if the risk is low and deemed acceptable