PROACTIVE MAINTENANCE

WITH SO MUCH REVENUE ON THE LINE, IT IS IMPERATIVE TO TACKLE MACHINERY PROBLEMS BEFORE THEY RESULT IN UNPLANNED SHUTDOWNS

In this day and age with daily revenues for power and oil & gas producers exceeding $1 million (and in many cases over $5 million), it has become imperative to tackle machinery problems before an unplanned shutdown. Yet, in the author’s experience, this is rarely the case. However, through the increased accuracy and quality of instrumentation and data collection, it is much easier to diagnose potential issues (via proactive maintenance) before a failure.

As a result of modern tools, there are an almost unlimited amount of possibilities when it comes to monitoring machinery condition. When we typically look at the Distributed Control System (DCS) in any plant for a specific machine, we see an array of screens that offer process conditions (driver and driven), mechanical data (bearing conditions) and auxiliary system condition (lube and seal oil or seal gas systems). These screens are valuable, but we do not see the internal condition of the machines (performance).

Using instrumentation that provides data for the process condition screen, we can use the instrumentation tag numbers that are built into the DCS to calculate head, efficiency and power in real time. This information can be plotted automatically on performance curves which could be imported into the system, or better yet, trended with all of the information on the other screens (vibration, lube oil temperature, primary vent flows, and so forth), allowing us to act when we see a change in the condition of the machinery.

Integrating this performance monitoring data with bearing, seal and auxiliary system condition monitoring (component condition monitoring or CCM) in real time can bring about a major change in maintenance results. Further, this opens the door to being able to trend critical parameters and develop historical data on component functionality.

The next logical question is: how can we possibly monitor each parameter for each machine and notice small changes in all of these parameters? Again, thanks to technology and the capabilities of new software, we can set up an alarm before the actual alarm, or what we call “soft” alarms.

The alarms would not be on the DCS but rather in the software that condition monitoring groups use. That way, the condition monitoring group can see component deterioration prior to the real alarm limit (which is usually too late to fix without shutdown), giving them time to act and correct the issue before having to shut down the equipment.

Selection of the soft alarm limit will vary depending upon the parameter and application. But as an example, a 30% change in phase angle would be a limit to indicate that fouling is breaking off of the impellers (this would have to be verified with performance monitoring, of course). This approach has been successfully applied to vibration, phase angle and even performance, but the ceiling is unlimited.

Although we are in the age of technology, we still cannot monitor everything remotely or on a computer screen. This is most true when it comes to auxiliary systems since there are so many components involved and some of them can only be observed in the field. This is becoming less and less the case with the introduction of components such as electronic valve position indicators, however there are items we will always have to visit in the field in order to monitor.

For example, we need to be in the field to monitor the condition of the trip lever on a MOP (main oil pump) steam turbine, if there is water in the bearing housing of the MOP steam turbine, or the pressure safety valve’s passing, etc. As one can see, the list goes on and on of components in an auxiliary system that need to be monitored locally. This is why an audit of these systems is a critical step towards proactive maintenance. Field audits on auxiliary systems are an essential ingredient in establishing the condition of components.

Let us take the case of a lube oil system. Typical parameters to be tracked and observed locally for a lube oil system include oil reservoir, pumps couplings, turbine driver, motor driver, valves, coolers, filters, accumulators and the lube oil tank. But this is far from all the factors that would need to be watched.

The point is that by combining local observations with automatic collection harnessing modern monitoring systems, we can proactively diagnose problems. And that could well be the difference between addressing any issues detected before they cause an unplanned shutdown, not after. The cost of instituting such an initiative is a small price to pay compared to the hefty penalty occasioned by a forced shutdown.

Author

Michael Forsthoffer holds a BS in Mechanical Engineering from the Rochester Institute of Technology and is currently working as a Senior Rotating Equipment Consultant for Forsthoffer Associates, Inc. For more information: michael@forsthofferassociates.com.