Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Reliability Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation




Machine Design - Case Study No. 100: The Value of Having Equipment Inspection Doors


One very important aspect of equipment reliability is inspection, and the ease in which an inspector can gain access to the critical components within the equipment. The easier it is to inspect the equipment, the quicker and more accurate the diagnosis. Yet equipment is continually being designed with little regard for this very important aspect.

Typical Screw Conveyor

It must be that the demand for it isn't great enough. In any industrial environment that operates around the clock, this type of oversight is unacceptable. The lesson learned in the following example can be applied to any type of equipment. Take for example the screw conveyor shown in the picture to the left. While walking past it one day, I heard a periodic thumping noise coming from it. I knew that this meant trouble, so I stopped for a moment to see if I could determine the cause for the noise. If I could inspect it quickly then I could write a work order to fix the problem. Being able to determine the cause for the problem would make repairing it simpler and quicker. Even if the problem wasn't identified, several possible causes could be readily eliminated, and that always helps when requisitioning parts and scheduling manpower. There would probably be parts to order, and not everything was carried in the company's warehouse inventory. Some parts are too expensive to keep in the warehouse, while others have very long lead times to get them from the equipment vendor. However, the brief inspection could not be done because there was no means to inspect the critical components of the screw conveyor. The conveyor's covers were locked onto the top with clips that required tools that I did not have in my possession. Even if I could pound the clips loose, there was always the chance that the oversized covers could slip into the conveyor trough and cause further problems, as well as a risk to my own safety. There was no way to safely grab them. So the only thing that could be done in this case was to write a work order to "repair as required."

Screw Conveyor Equipped for Easy Inspection

This type of work order is frustrating for the maintenance planner because it is hard to know what to plan and how much manpower might be required. Of course the Production personnel then infuriate the poor maintenance supervisor by asking the usual question "how long will it take?" The maintenance supervisor answers back "How long will what take? I don't even know what's wrong with it yet!" So, what does the maintenance supervisor do AFTER he gets burned on this job? He makes it easier to inspect the equipment the next time. A good example of an easily inspected screw conveyor is shown in the picture to the left. This particular screw conveyor had eaten the maintenance supervisor's lunch, and then some. Notice how there are handles on the smaller lids which do not require any tools to remove. Also, there are inspection doors located over the critical internal screw components. Notice in the picture to the lower left, how the critical components can be easily inspected. The brackets that support the screw sections, the hanger bearings, and the screw couplings. All of these can be easily, safely, and quickly inspected without the use of any tools. Therefore, anyone walking by can open the inspection door cover and get a quick look inside if they want to do so. Screw Conveyor Inspection Door


This is just one example of making it easier to perform a quick and safe inspection; it can be applied to any type of equipment. Simply put, the more inspection a person can do while the equipment is running, the better the planning will be for the eventual repair. When the equipment does come down, the job will go quicker, and the equipment will be running again sooner.

Manufacturers are not going to volunteer equipment that offers inspection ports, and the like, unless it is in the customer's bid specification. Why isn't it going to be volunteered? It costs money to put extra stuff into equipment and that raises the price. In a bidding war, manufacturers cut all of the fat. Any "extra" that isn't in the bid specification is deleted. Therefore, if you want equipment that can be easily inspected, make sure you let your resident maintenance expert review the equipment and let that person make suggestions as to how to make it easier to inspect and/or gain access to critical components. And then you know what you do? ...



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