Maintenance is a fact of life in the processing industry. Every piece of equipment that is in operation will eventually fail and require maintenance. This adage is especially true when it comes to instrumentation. It has been reported that processing plant instrumentation requires maintenance at a rate of nearly 15% per year. This can be a considerable expense and have a significant impact on a company's profitability. A significant number of maintenance problems are not directly attributable to the equipment per se, but, rather, to the human performing the equipment installation and the operator's ability to trouble shoot system problems.
A paper given at Texas A&M's 49th Annual Instrumentation Symposium, "Reducing the Cost of Manufacturing," H.Sinclair, The Dow Chemical Company, provides some interesting insights into the instrumentation maintenance activities at one company. In the paper, Dow conducted an internal audit that looked at the instrumentation problems that were reported on their maintenance work requests. Among their findings was that "routine checks" accounted for approximately 21% of the work requests and "no problems" were found on 17% of the work orders. Such a large percentage of time spent diagnosing instrumentation that has no problems presents a significant opportunity to reduce maintenance costs. The real question was to find out what was causing the "no problems" work orders.
After examination of more of their maintenance data, Dow concluded that 1) poor installations lead to accuracy problems, 2) accuracy problems cause zero adjustments and recalibrations, leading to distrust of the instrument, 3) the distrust leads to routine checks and "no problems found" work requests, and finally 4) poor installations cause more maintenance than instrument failures. Actual instrument failures accounted for less than 3% of the problems.
Although not as well studied and documented as Dow, others in the processing industry have had similar experiences and have chosen to empower their operators as a solution. To help reduce the "no problems found" work orders, some have begun to train the operators on basic instrument troubleshooting and simple repair. Giving the operators basic instrument diagnosis skills not only helps reduce the number of "no problems found" work orders but also gives the operators more confidence in the instrumentation. It is fairly common practice today to have a few specially trained operators that can diagnose simple instrument problems, such as plugged transmitter lines, and perform simple repairs, such as blowing down the transmitters.
A final interesting conclusion from the study was to quit using digital switches. Dow has found them to be too unreliable and a significant cause of process plant upsets. Instead, Dow has chosen to use low cost, low accuracy transmitters that can be quickly checked to determine if the device is functional.
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