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“A NO-BRAINER,” “Mom and apple pie,” “So obvious, it’s barely worth discussing.” These are some of the immediate responses from systems and instrumentation suppliers and users when asked how maintenance and operations departments should go about justifying investments in HART technology to plant managers.
But a no-brainer to a plant maintenance manager may not necessarily strike the same chord with a senior financial manager. Consequently, personnel who want to start reaping the benefits of HART need to develop strategies that take into consideration the HART capabilities the facility already has (e.g., installed HART instruments, HART I/O, etc.), additional investments needed, and the benefits the company will realize from those expenditures.
The no-brainer attitude stems from the fact that most plants already have made substantial investments in HART technology. So, say the experts, it only makes sense to put those capabilities to use.
“If you’ve bought 4-20 mA instrumentation in recent years, chances are good that it’s already HART-enabled,” says Prasad Raghavendra, a systems product manager for Honeywell. “And if you’re considering buying new instrumentation, the incremental investment in buying HART-enabled devices rather than those capable of only 4-20 mA is extremely small. So it becomes easy to decide to go with HART without having to make a big case.”
If you’ve purchased your control system during the past few years, odds are good that it has native HART I/O, meaning you can bring the digital HART signal, including diagnostic information, secondary process variables, etc., directly into the system.
In addition, HART communication operates over existing wires, so much of the physical infrastructure you need already is in place.
Most plants, however, will have to invest at least a small sum in equipment and/or software to take advantage of HART capabilities. These include HART multiplexers, which strip the HART digital signal from the 4-20 mA signal and route it to PC-based software applications equipped to accept HART input; and HART modems, which are PC I/O cards that enable users to communicate with devices via HART.
In putting together a case for those investments, maintenance and operations departments should stress to management the situations that won’t occur as a result of using HART. Specifically, HART will enable plants to avoid unplanned shutdowns and unnecessary maintenance, particularly on valves.
“You’re going to make your workforce more efficient, because you can get them focused on working on the right stuff,” says Jim Cobb, marketing manag er for Emerson Process Management’s Rosemount Division. “This is especially true of the valve diagnostics. It’s probably the one that hits you right in the face.”
Being able to keep an eye on valve performance via HART and compare it against valve signatures will reveal to plants when the device actually needs maintenance.
‘If your current mode of maintenance involves shutting down every six months and checking valves, transmitters, etc., the use of HART may enable you to reschedule and reduce those activities,” says Marcelo Dultra, vice president of sales and marketing for Smar International. “If you can show that a valve can run eight or nine months, you might not have to shut down every six months. There’s enormous value in that.”
INTELLIGENT FIELD COMMUNICATIONS
IN PLANTS THAT employ safety systems, testing safety valves periodically is absolutely essential. After all, the last thing you want is for a valve to stick in an emergency. Under IEC and ISA safety system standards, a plant system’s probability of failure on demand can be reduced by increasing the frequency of system testing. Increasing frequency once was impractical for many plants, since valves could only be tested during shutdowns. However, plants now can run partial-stroke tests in which a valve is moved only a small percentage of its full range, to ensure that it functions properly in emergencies. If the valve actuator is HART-capable, the device can confirm its actual movement to operators and maintenance personnel.
Even in terms of day to day safety for workers, HART can play an important role. Norit Americas manufactures activated and reactivated carbon at its plant in Pryor, Okla. The manufacturing process requires the usage of acid, coal, steam, burners and compressed air, creating a hazardous work environment. By replacing conventional analog monitoring devices with HART-capable devices, maintenance personnel are able to run diagnostics and perform calibration checks and even make adjustments from the safety of the equipment control room through the use of a handheld set. In addition, the plant recently installed an asset management system workstation in its maintenance building, allowing personnel to work on HART-capable devices without leaving the structure.
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