Repair or Replace- The Bathtub Curve
Repair or replace, that is the question. Or at least it would be if Shakespeare had worked as a maintenance manager in the 21st century. Engineers in FM Industry often come across this dilemma while performing maintenance schedules. The choice between repairing or replacing a piece of equipment is a maintenance manager’s worst nightmare. Unfortunately, most times, there isn’t a single, easy formula for you to follow to get your answer. You need to assess several factors before reaching your final decision. But there are three prime points of consideration to decide easier.?Costs, efficiency and age.
But before we get there, let's understand the "bathtub" curve.?A bathtub curve represents the probability of a certain asset failing over time. It allows us to clearly map three distinct phases in the asset’s life cycle, (see fig). Childhood, Youth?& Old age??Understanding these three stages enables us to adapt our maintenance plan throughout the lifecycle. Since the bathtub curve helps us determine the asset’s expected useful life and reliability, it’s easier to keep it under control. But the chief advantage is undoubtedly being able to more accurately plan?how?and?when?to perform maintenance. The ultimate goal, as always for facility managers, is to extend the asset’s useful life and increase availability without unnecessary maintenance. Lets understand these three stages in more detail.
Youth / Useful Life and Random Failures At this point, the maintainer and the machine are more or less in sync like a perfect marriage. The failure rate is constant because maintainer knows how to handle it, and the manufacturing errors were fixed. This stage is popularly known “useful life”. Even if major failures occurs , those are largely attributed to human errors, overuse or overload, and accidental breakdowns. Otherwise the failures are mostly predictable. This is BAU time for facility manager and a perfect diagnose to this would be follow the manufacturer’s advice for periodic maintenance. Some call is preventive maintenance. A few evolved FM companies take this to the next notch of predictive maintenance. A PdM (Predictive maintenence) enable us to foresee failures in the most athematic and logical and bring down the down time considerably.
?Old Age/ End of Life: I would call this as the most challenging phase in maintenance manager's career. Old facilities are litmus test for a FMs knowledge and experience. The failure rate here are high and the bathtub curve function has a positive slope. Not necessarily all assets come to this end, as few clients believe in phasing out them before their wear-out stage. Or the equipment might have got a mid life upgrade due to some replaced parts when their technology becomes obsolete, even though they are still working. At this stage, failures are a result of wear and tear, poor maintenance. Repairs get more expensive and security risks are high. The best maintenance regime here would be preventive maintenance, which is more effective in preserving reliability and extending the useful life. Ideally one should establish new preventive maintenance routine measures as soon as you notice an increase in the failure rate. Few measures could be to (a) Do to compromised on quality of spare parts (b) To keep equipment in ideal temp and Rh level (c) Make and strictly follow a details PM Plan and a ideal scenario would be if one has past algorithm of PdM and Breakdown maintenance. But despite all these the failure rates will go up.
领英推荐
This stage is where the three factor of age, efficiency and cost come into play .
Costs. This is the most crucial factor that any client would first consider. The cost of a new?piece of equipment is easy to determine, but calculating the costs of repairing a current asset is a different story. A FM while doing this may have to look at all the costs associated with the repair including spare parts, labour costs and most importantly the business losses that may occurs due to downtime. These calculation will help make an estimate of the maintenance cost of a new?piece of equipment vs an old one. One important fact that FMs needs to consider is MTBF (mean time between failures). Thus if the total spent on repairs is more than 50% the price of a new?piece of equipment, replacing is probably the best option.
Age. Unlike a fine wine, machines do not get better over the years. However, there is one similarity between the two in that they do both get more expensive. As time passes, it becomes more and more difficult to find spare parts and, in some cases, it becomes impossible to find parts like the original ones. A piece of equipment that is nearing the end of its life expectancy carries more maintenance costs, both preventive and corrective. Therefore, always review carefully all the data you collected about its operation before you decide to repair it! It may just be time to bid your fairwells to that faithful DG that was lighting up your facility all these years.
Efficiency. Efficiency in terms of energy costs, older machines have a lower energy efficiency rating. This means they are less efficient in terms of energy consumption than new equipment?as well. When it comes to safety, older equipment is often associated with a higher risk of accidents, which can pose a real danger to your team.
So, as with costs and age, the efficiency of equipment may ultimately determine whether you should repair or replace it.