Everyone appreciates the potential value of predictive maintenance. After all, spotting situations before they cause significant problems means that maintenance generally can be planned so the right parts and people are available and work is done when it least impacts operations. This clearly saves money and minimizes downtime. However, actually achieving predictive maintenance can be tough. It requires a culture change at most plants. In addition, it demands diagnostics that can provide a suitable heads-up to budding problems.
Developments in diagnostic technology are certainly helping. For instance, as Mike Spear explains (p. 23), instrument companies now are making sound use of electrical and acoustic noise to get an early warning of problems with process measurements and to pin down their causes. This pays off not just in maintenance but in better monitoring and control.
In addition, new types of instrumentation, designed for diagnostics, are emerging. For example, on-line corrosion monitoring is increasingly replacing traditional techniques like coupons. It can distinguish between localized and general corrosion and not only give a heads-up on hardware condition but even can help plants identify process disturbances that lead to corrosion spikes, so they can be avoided.
Similarly, new technology is challenging traditional vibration monitoring. At the 2007 North American Foxboro User Group Conference in mid-July in Boston, SWANtech demonstrated an instrument that uses ultrasonic stress wave measurement to monitor the friction of rotating equipment as well as load changes and shocks. Its technology provides the earliest detection of equipment damage as well as a way to quantify and trend wear, according to the Ft. Lauderdale, Fla., based unit of Curtiss-Wright Corp. The technology reportedly is so sensitive that it can detect sub-surface micro-fracturing and the differences in effectiveness among lubricants.
Having more and better data isnt enough, though. Plants must go from condition monitoring to condition management, noted Neil Cooper of Invensys at the Foxboro meeting. This means moving from just collecting data to putting the data into context and effectively dealing with the information.
Id add that plants need more than predictive maintenance and condition management. They need to avoid problems outright, making maintenance unnecessary or at least minimizing it.
One key to success here is proper equipment selection. Yet, as plants lose people with expertise, more mistakes undoubtedly occur.
Consider the ubiquitous motor. Choosing a replacement motor of the same horsepower and mounting isnt enough, stresses Dan Snyder (see Get your proper bearings) the wrong bearings can significantly shorten motor life. The service and orientation of the motor greatly influence what type of bearings should be in the unit. A motor directly driving a load generally needs different bearings than the same-size motor handling belts. Installing a motor designed for horizontal service vertically may cause a loss of grease in the bearings.
In addition, minimizing stresses on equipment during startups, shutdowns and infrequent operations certainly can play an important role in maintaining the health of plant hardware. Here, too, we face challenges as skilled operators retire and dont effectively pass on their experience and expertise. Even if youre lucky enough to still have top-notch operators, performance from shift to shift undoubtedly varies because some people simply have a better feel for the process. However, as Pat Kelly explains (see Help your operators), control systems can capture best practices and procedures and so help operators do their jobs better and more consistently.
Maintaining what weve been doing just isnt good enough anymore.