New approaches to capturing field-generated information about mill machinery are giving operating and maintenance personnel greater knowledge of the condition of their equipment than ever before, enab…
New approaches to capturing field-generated information about mill machinery are giving operating and maintenance personnel greater knowledge of the condition of their equipment than ever before, enabling them to improve performance and increase productivity. The latest automated systems deliver timely warnings and actionable information on rotating equipment so upsets can be prevented before they happen.
Process industry personnel have long recognized the value of field-based information for use in maintaining equipment to avert unexpected downtime. However, sending people into the mill to diagnose suspected problems often resulted in reports of “nothing wrong” or “no corrective action taken” because they couldn’t “see” into the process. Equipment kept failing unexpectedly, causing process upsets and unplanned outages that result in lower production rates and higher costs.
Many of those maintenance-related trips into the mill to evaluate a pump, motor, control valve, or some measurement instrument have been eliminated by new technologies capable of gathering detailed information on the health of production assets.
Things began improving 20 years ago with the introduction of the first smart field instruments with embedded microprocessors that could transmit both process measurements and information about the condition of plant equipment via 4-20 ma analog signals back to central locations. Soon, smart control valve positioners were developed to diagnose existing or emerging problems with critically important control valves.
Asset management software was created to capture these diagnostics, organize the data, and present it in a logical manner for use by maintenance personnel in determining courses of action.
Hardware and software products for vibration analysis of rotating machinery were developed in Knoxville, Tennessee, to help maintenance personnel gain advanced knowledge of impending equipment failures in order to prevent breakdowns. Two different technologies evolved. Portable or route-based vibration monitoring has become a common means of obtaining information to identify potential problems with rotating machinery. Data gathered periodically in the field using portable measuring devices on selected machines is later uploaded into a computer for review and analysis.
A more automated online vibration monitoring system involves permanent instruments typically installed only on expensive pieces of equipment such as steam or gas turbines, generators, compressors, and paper machines, which are critical to the uninterrupted operation of a mill. Continuously gathered data are transmitted to a central location for study by a vibration analyst.
The science of tribology, which finds machine faults through oil analysis as well as ultrasonic examination and thermography, provides additional useful information. By combining tribology, ultrasonic, and thermography solutions with vibration analysis, trained personnel are able to “see inside” rotating machines to determine when maintenance should be performed.
Predictive maintenance
Information captured by various advanced technologies can be used to reduce mill maintenance costs, extend equipment life, and increase overall mill reliability. Field-based information gives personnel a new perspective on the operating condition of their rotating machinery, field devices, and control valves, enabling them to take appropriate action as necessary to prevent unexpected failures and emergencies.
Armed with newly available field-based information on the actual condition of operating equipment, operators and maintenance personnel can make more informed decisions as to when repair work should be done. They can predict with reasonable accuracy when each pump, control valve, or field instrument will next need maintenance in order to preserve its performance. The idea of predictive maintenance is to service equipment in time to minimize physical deterioration and unexpected failures while maintaining acceptable performance as long as possible.
Most effective is a combination of predictive and reliability-based maintenance. Under this concept, all machinery is prioritized in order of importance to the overall mission. Obviously, critically important equipment must be maintained for maximum reliability, but it may not be necessary to give that same high level of care to everything in a mill. Some machinery may even be allowed to run with minimal attention, if that will not adversely affect the overall operation.
What end-users want
Real opportunities remain for technology-driven improvements of both operations and maintenance in pulp and paper mills. Recent face-to-face interviews of more than 200 individuals in pulp and paper mills, refineries, chemical processing plants, and power stations revealed a strong interest in further automating the collection and analysis of operating data on rotating assets. Specific needs expressed were:
* Continuous monitoring with updates within 60 seconds so operators can react quickly
* Integration of machine health information with automated control systems
* Centralized problem-solving to eliminate excessive trips to the field
* Diagnostic information provided for decision-making rather than just raw data
The results of this survey stimulated a groundbreaking development program at companies such as Emerson to find new ways to prevent unexpected failures and avoid process upsets. By applying their expertise in digital plant architecture, predictive diagnostics, asset management technology, and Foundation fieldbus communications, as well as vibration monitoring and analysis, the engineers created a whole new generation of field instruments to better identify undetected equipment faults. These devices not only gather information from multiple data sources, they continually analyze the health of mechanical equipment and transmit reliable information to those with authority to make changes. Designed to function with all the interoperability of Foundation fieldbus devices, this technology facilitates communications with any fieldbus compliant control system host. As such, it works exceptionally well as a part of Emerson’s PlantWeb digital plant architecture.
Operators see a simplified presentation of the current operating condition of each monitored machine. An overall machine health value, based on various physical characteristics, can be assigned a numerical rank from one to 100 with the top number indicating 100 % health. Alerts identify changing conditions that need attention. Operators don’t have to interpret these inputs; they can use the actionable recommendations provided at the same time to alter the process to avoid an upset. If necessary, the maintenance department is asked to evaluate the data to determine when repairs should be made.
Those interviewed in the end-user survey identified motor/pump trains as ideal candidates for continuous monitoring and automated analysis. Such units account for approximately 60% of the rotating machinery in a typical mill, and many are considered essential to the production of pulp and/or paper. Bearing failures, misalignment, cavitation, and imbalance were singled out as the most frequent and severe problems.
New smart transmitter
For the first time, detailed data regarding vibration, temperature, motor flux, and shaft speed of AC induction motor/centrifugal pump trains can be monitored and analyzed automatically in the field by the new CSI 9210 machinery health transmitter made by Emerson. Motor/pump units tend to have similar failure patterns, which the embedded intelligence recognizes. This enables the device to transmit actionable information to the host in the form of alerts and recommendations. The delivery mechanism is the same as that for smart fieldbus instrumentation and valve positioners. Mill personnel can observe what’s happening inside th
e operating machinery, and they receive advice regarding best responses.
Successful beta testing began in January 2004 at ten sites in North America under environments ranging from extended periods of below freezing temperatures in Canada to hot and humid exposures near the Gulf of Mexico. Throughout this period, no device failures occurred. Meanwhile, the analysis logic was enhanced and refined to ensure correct detection of motor/pump train problems.
While mill personnel with minimal knowledge of vibration analysis methods can install and configure the transmitter, installation and support services are available to ensure users receive full value from this technology. This transmitter is not unlike other smart instruments with respect to configuration and commissioning.
With transmitters in place at essential pumping points, control engineers and operators can see in real-time the dynamic interaction between the process and motor/pump units and the effect that the process has on the health of the machinery. For example, if a process situation causes pump cavitation, that condition will be relayed to the control system, so operators can take whatever action is necessary.
John Rezabek, a controls specialist at ISP Chemicals, Lima, Ohio, and an early user of the new technology, commented, “Our operators are alerted in real time when equipment problems start to manifest. If a change in upstream head, volatility, or composition results in increased flashing or cavitation, they can make adjustments to eliminate the problem.”
Changing procedures
It does little good to buy and install the latest diagnostic systems unless appropriate work practices are put in place. For example, many schedule-based maintenance tasks are delayed or totally eliminated by reliability-based maintenance, since this requires allocating resources where they are most needed. Such changes, which require a willingness to accept new maintenance procedures, may be difficult for some maintenance organizations to implement.
Too many companies invest in technology and expect a big payback without training personnel to utilize the information and without changing maintenance practices accordingly. Once an advanced technology is installed, managers need to examine existing work practices to see what tasks can be streamlined or eliminated. Personnel who understand what technology is telling them are generally more able to accept new procedures.
Having reliable field-based information readily available empowers operators to improve plant availability and performance, while early warnings enable maintenance personnel to avert unwanted upsets and unplanned downtime.
Brian Humes is the vice president and general manager of Machinery Health Management in Emerson’s Asset Optimization Division, Knoxville, Tennessee.
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