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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.
THE HART DIFFERENCE
Two Simultaneous Communication Channels
35–40 Data Items Standard in Every HART Device!
OBVIOUSLY, no two plants are alike, and results that each can achieve through use of HART can vary widely. Based on their experience working with a wide variety of users, systems and instrumentation vendors have come up with a number of implementation tips to consider and pitfalls to avoid:
Implement Solutions Gradually
Emerson’s Cobb notes that HART can be effectively implemented gradually, by tiers, making it easier to budget investments over a long period.
”At the low end of investment, you can stay offline and simply monitor loops on a manual basis periodically. This can be done in the field with a handheld communicator or by hooking up a PC equipped with asset management software, including data on all your instrumentation,” says Cobb. “At the next level up, you can establish continuous monitoring via a separate asset management system. And, beyond that, if your plant has invested in a control system with HART I/O, you can bring the secondary variables directly into it.”
Rely on Existing Equipment
Rely as much as possible on existing equipment says Steve Todd, marketing director for Moore Industries, which manufactures HART multiplexers. "We've found that customers that stand to gain the most from HART technology are the ones that can leave as much existing equipment in place as possible, yet still make significant, cost-effective process improvements. For example, if a customer wants valve position feedback at the control room, he can go the traditional route and run additional wiring back to the control room that provides this data. This gets expensive fast. A second alternative, though, is for the customer to leave everything else alone, and install smart HART controllers on the existing valves. Then, extract the stem position data from the HART digital data using a HART interface instrument installed in the control room.”
Demand Interoperability From Vendors
“While HART is a very open protocol, not every company subscribes to it,” says Honeywell’s Raghavendra. “Consequently, buyers should make sure from their vendors that the field device and/or system fully complies with the protocol as defined by the HART Communications Foundation. Customers also should encourage their vendors to register their devices with the foundation.”
Be Specific About Your Goals
Be specific about how you want HART to meet your needs, advises John DuBay, instrumentation product manager for Meriam Process Technologies. “Predictive maintenance is a great story, but many end users aren’t sure what diagnostics they’re looking for. If you ask them about the specific diagnostic capabilities they’re interested in, they’re not always sure.”
Provide Easy Access to HART Data
To achieve the benefits of online configuration and diagnostics, operations and maintenance personnel need to cooperate. However, that situation often is the exception rather than the rule, says DuBay. “Not many operators are eager to open up access to their maintenance crews because they’re fearful that devices could be reconfigured incorrectly or by accident.”
Know Where the ROI is Coming From
Masoneilan Digital Product Specialist Sandro Esposito advises that users should not expect to get substantial maintenance-related ROI from new HART-enabled digital valves. “The big rate of return is on the existing valves,” says Esposito. “You can graph a valve's performance over time and see that it plateaus at a high level of performance when it's new. You want to know where's the drop-off from that plateau, and how steep it is.”
INERGY, HEADQUARTERED in Kansas City, Mo., is a major provider of propane and services to 600,000 customers. While most of its operations are in the Southern, Midwestern and Northeastern states, the company operates a natural gas liquids site in Bakersfield, Calif., that includes processing, storage and terminal services.
Propane manufactured at the facility is stored in bullet tanks, each of which holds 10,000 to 15,000 gallons of propane. It is critical for the company to monitor levels and temperatures in each of the containers, since propane expands as temperatures rise. If pressure increases too much, the company must vent gas into the atmosphere and risk violating stringent California environmental regulations.
Ken Clifton, instrumentation and electrical supervisor at the plant, says personnel used to rely on sight glasses and “spinner” gauges mounted in the tanks to visually judge levels. “Our people would have to actually go out there and look at the tanks to determine the levels,” he says, adding that it was inefficient.
To improve the situation, Inergy decided three years ago to install field instruments in each tank that would send readings on temperature and level back to Inergy’s control system. “We could have put separate temperature and level transmitters into each of 40 tanks, but that involved quite a bit of instrumentation and wiring. Instead, we purchased instruments from K-Tek, each of which was able to monitor both of those variables,” says Clifton.
The transmitters send 4-20 mA level readings back to the plant’s programmable logic controller equipped with a HART gateway and use a HART digital signal to communicate temperature and level information. Using the two readings, the system is able to calculate the level in each tank accurately and display it on the system’s HMI.
“With this system, we’re able to get two readings for the price of one, and it’s worked well for us,” says Clifton. “We’ve had a few minor problems, but none involving use of the HART protocol.”
“In fact,” adds Clifton, “all the instrumentation we put in this plant has the HART protocol, because it makes troubleshooting easy for our instrumentation techs.”
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