Condition monitoring, the right way
Condition monitoring (CM) has become a fairly standard part of any successful maintenance program, but it is not always well understood. Some believe doing it on its own is enough. Others believe it will prevent failures. Others think overhauling equipment is a form of CM. They’re all mistaken, and unless you’ve given some serious thought to how often you are doing your monitoring, you could be doing it far too infrequently.
In CM, we check the condition of equipment, usually through one or more indicators (vibrations, temperatures, oil condition, ultrasound, etc.); we determine if it is still good and, if so, we do no more. It does not prevent failures: it can only detect them in their early stages before the equipment deteriorates beyond functional usefulness. Therefore, CM provides an opportunity to plan and schedule any needed corrective work. Those who fail to follow up miss the opportunity and end up with the very consequences they wanted to avoid by doing CM in the first place.
Overhauls are also often mixed up with CM. Some believe an overhaul is intended to facilitate inspection to determine if the equipment is still in good condition, but that is perhaps its least appropriate use. We overhaul on fixed intervals if we know of wear, erosion, corrosion or fatigue will almost certainly have progressed to a point where we need to replace or restore components. When you do an overhaul you should expect deterioration to be evident and you should always have the replacement parts on hand.
Not all that long ago, CM techniques were not as advanced as they are today, so stripping equipment apart made sense in some cases. Today, however, we can avoid that by using one or more non-intrusive CM techniques. They detect condition without any need to shut down, isolate, strip, inspect, reassemble and re-commission. Usually the equipment must be operating for condition monitoring to work.
Having said that, there are some failures that do require overhaul work, so CM may be unnecessary. Simply run the requisite hours, doing the overhaul at the scheduled frequency comfortable in the knowledge that you will be replacing aged or worn components and restoring equipment condition. Bear in mind, too, that this type of work should make up only a small portion (say 12 to 15 percent) of your entire maintenance program. CM should make up about 25 percent — and that does not include the work arising after you have done the monitoring.
So how often should you do CM? The frequency of monitoring should be determined using the length of time it can take from the point at which you can first detect deterioration to the point where the equipment fails, known as the “Potential Failure to Failure (P-F) Interval.” If you monitor once a month and your P-F interval is only two weeks, there is a good chance you will miss the deterioration on your check. In that case, you should check at intervals of less than two weeks to provide the needed planning and scheduling lead time. In that example, I’d check once a week.
One client, a major company, had a contract do vibration analyses every six months on major equipment. They almost never found defects, but they did experience the odd failure between vibration checks, which always cost them millions. I recommended that they save their CM money or increase the inspection frequency to weekly. In that case, it would have been best to hire and train a technician rather than use the contractor. Preventing any one of the failures they had already experienced would have paid for them many times over!
If you are new to CM, there is much to learn. Don’t just believe the hype from salesmen. Get some serious advice from those who truly understand it before you waste time, money and opportunity.
James Reyes-Picknell of Barrie, Ont.’s Conscious Asset Management is a certified management consultant specializing in operations excellence and asset management. You can reach him at email@example.com.