Inspection and Prevention Improve Reliability

Repair before failure, but ensure maximum component life, too

Construction Equipment - January 1, 2005

Mike Vorster
Contributing Editor

Successful equipment managers focus on reducing unscheduled field breakdowns and improving machine reliability. They emphasize prevention rather than cure and understand that actions taken before failure are more cost-effective, less disruptive, and easier to manage.

On the other hand, many believe that replacing components and taking action before failure is a conservative and expensive thing to do. If a component is supposed to run 5,000 hours, why replace it at 4,500 hours; let it run to failure. It may last 6,000 hours, and early replacement would waste 1,500 hours of component life.

The proponents of a run-to-failure philosophy have a point. If the breakdown does not have a high impact, or if you are not concerned about the impact, then it may be the right strategy to let components run to failure and extend life to the maximum.

Which strategy is better?

We can gain some insights into the difference between a conservative repair-before-failure approach and a crisis-based run-to-failure alternative by understanding how components wear out and eventually break down.

First, most components wear out over time and provide plenty of warning. Hydraulic cylinders leak, hoses chafe, engines smoke, and cooling systems overheat. Few components fail without some kind of warning. We can, in most cases, choose to neglect the warnings or respond to the warnings.

Second, signs of impending failure can be either clear and easy to see or hidden and difficult to detect. You can see a leaking hydraulic cylinder or a cracked boom, and it is no secret when cutting edges need replacement. On the other hand, it is not easy to see a bearing that is slightly out of alignment, a shaft that is not running quite true, or an injector that is not performing.

Let's use this understanding of how components fail and of how easy it is to detect signs of impending failure to develop the matrix shown on the following page. The timing of the action defines the columns and our ability to detect signs of impending failure defines the rows. This gives four possibilities:

1. Signs of impending failure are clear, and we take action before failure (cell "A"). This is the simple, straightforward and correct action. Our preventive maintenance technicians advise us of cylinders that are leaking, hoses that are wearing out, and engines that are using oil. We take timely action, solve the problem, and prevent the failure. The system works, and we are doing the routine and expected part of our job.
2. Signs of impending failure are clear and we experience a failure (cell "B"). We are, quite simply, not doing our job. Not only has the machine broken down, but also our systems have broken down. We either did not notice that the cylinders were leaking or we did notice the problem and could not take timely action. In the end, it doesn't matter: A clearly avoidable failure has occurred. Disruption, downtime and cost are unnecessarily high. We need to change our system.
3. Signs of impending failure are hidden, and we take a conservative repair-before-failure approach (cell "C"). Transmission life is expected to be between 7,000 and 12,000 hours, so we bring the machine in and replace the transmission at 8,000 hours just to be sure. We achieve cost savings by taking action before failure, and unplanned downtime is eliminated. But, we wonder if the transmission could have run for 12,000 hours or was impending failure just around the corner? Was it really the most cost-efficient solution?
4. Signs of impending failure are hidden; we let the component run to failure and repair it when needed (cell "D"). The transmission fails at 9,000 hours; the whole operation grinds to a halt; and we rush out a replacement machine. Rebuilding the transmission takes place under crisis conditions; it is more expensive than necessary; we have to wait for parts; and downtime adds up. We gained another 1,000 hours on the old transmission, but the unplanned failure was expensive and disruptive. Was it really the most cost-efficient solution?

Both C and D provide grounds to question our actions. We may be wasting component life by repairing before failure, or we experience unplanned downtime and impact production. Options A and B are easy: We must increase A and eliminate B.Two strategies must be employed to resolve the dilemma. The first focuses on moving line "XX" to the right by increasing the amount of effort placed on repair before failure.The second focuses on moving line "YY" downward and increasing the amount of effort placed on inspection and diagnostics that help detect impending failure in expensive components. Inspection and prevention work hand in hand to increase the size of cell A and do as much work as possible based on inspection and hard data rather than conservative component-life statistics. Inspection removes the nagging doubts about whether or not a component could have run the extra 4,000 hours and gives the confidence needed to prevent failures, improve reliability, and minimize disruptions to production.