Do more with less. That's the mantra of many industries today in North America or anywhere else around the globe. Companies no longer have employees that aren't fully utilized—nobody has a couple of hours to grab a clipboard and some test equipment and go out in the plant to check the condition of field devices and final control elements.
Besides, plants require hot work permits, safety information, workarounds and other time-consumers, making it highly unproductive to grab that clipboard and go.
Companies around the world have begun formal programs to use the diagnostic data in their HART-smart instruments and control valve actuators and positioners by directly connecting them to the asset management systems in the maintenance department.
"HART technology has saved both time and money," says Todd Gordon of We Energies in Milwaukee, Wis. "We have also used the HART signal from digital valve controllers (DVCs) or positioners to provide valve position to our DCS control system with the use of a HART converter module."
Why was this important? "Actual position feedback was not available with the original plant equipment, and we couldn't tell if a valve was sticking without physically looking at it," Gordon says. "With this HART signal converted to 4-20 mA for an input to DCS, we then added a deviation alarm to tell the control operator when the DCS command signal deviated from the actual valve position more than 5% for more than five seconds. This HART feature alone saved the plant from tripping offline on several occasions. We have been able to adjust valve packing on valves when they were in service, which is a huge benefit. We have also prioritized maintenance work based on the friction calculations of the HART smart positioners. The dampers with the highest friction numbers were repaired first."
Hiren Choksi, of Krishak Bharti Cooperative Limited in Gujarat, India, agrees. "Benefits are quite huge in terms of the monetary aspect, as well as it has helped by increasing the overall productivity of the plant. Let's say, in an ammonia plant, one unplanned breakdown shortens the life of reformer tubes by 7% due to thermal shocks. Using the HART protocol, faults and errors are able to be identified and rectified well in advance."
Tina Lockhart, director of engineering for Moore Industries International, says, "Every HART field device response contains information regarding the device's health. This information consists of device and variable status, such as device malfunction or primary variable out of limits. Having this data sent with every message provides the operator with confidence in the integrity of the process measurement and with immediate notification of a problem. From a maintenance perspective, a whole plant can be monitored from a single location, and fault diagnosis can often be performed remotely. Many instruments provide additional status information that can be used for predictive maintenance and replacement of equipment on an as-needed basis. This results in reduced maintenance trips, fewer process disruptions and high system availability."
Eddie Saab of Lakeside Process Controls in Ontario, Canada, talks about the use of HART diagnostics to correct serious problems at the Bruce Nuclear Power Station. "This is the largest nuclear power plant in North America," he says."Bruce Power had a history of feedwater heater operating problems. When a comprehensive root-cause analysis was initiated in 2001, it pointed to two main causes for the problems: an inverted loop in the saturated drains that allowed liquid to collect (which was corrected), and inadequate heater level control, which was solved using HART-enabled smart instrumentation."
Saab continues. "The Bruce Power/Lakeside process controls team decided to carry out what it called "smart utilization of smart equipment." Solenoids and junction boxes were integrated onto the valve assemblies. An interlock was tied in so that if power was lost to the solenoid, the positioner air supply was blocked, and the valve actuator used its spring to get the valve to the fail-safe position. The team used the HART signal inherent in the Fisher DVC6000 digital positioner to detect the solenoid trip. And, finally, the team set up the Fisher DVC6000 digital positioner on the valve to provide a direct signal for valve position and to enable on-line valve diagnostics."
Moving to Predictive Maintenance
"This approach uses two-way communication between the control room and the valve for on-line troubleshooting," Saab continues. "On-line troubleshooting is looking for advance signs of problems that could impact process performance. This allows the plant to move away from preventive maintenance, typical within the industry, and toward true predictive maintenance, a more effective way to address valve and process problems."
Kenneth Marse, of Galata Chemicals LLC in Taft, La., puts the value of HART for asset management simply. "The plant converted to contract instrumentation/electrical maintenance in 2007, and staffing was significantly reduced. Instrument reliability suffered, and calibration compliance declined. Using HART and the AMS system [from Emerson Process Management], the site has improved instrument reliability and has returned to full calibration compliance while maintaining a reduced staff."