Asset management is the most difficult thing many companies do—far more difficult than actually making the products their processes are set up to make. The reason, of course, is that asset management for predictive and preventive maintenance is an add-on function in most plants. When these plants were built, there were enough people available to walk around inspecting assets for potential problems, and forty years ago the cost of simply replacing all the critical valves or motors every time there was a shutdown was relatively small, and shutdowns were relatively frequent.
But that is no longer the case. Staff reductions have limited the number of people able to walk around the plants. Running the plant at over 100% of capacity and lengthening the times between planned shutdowns has made preventive repair or replacement of assets, such as valves and motors, problematic and expensive. And with longer times between shutdowns, unplanned shutdowns due to deferred maintenance have become both more frequent and more expensive.
"We bought the very first version of AMS 1.0 from Emerson in 1999," says Gàbor Bereznai, head of the automation and electrical department for MOL, the Hungarian refining corporation, whose Danube Refinery was the 2012 HART Plant of the Year. "We have AMS, PRM from Yokogawa and Honeywell's asset management software as well."
Bereznai says that the Danube refinery site has 40,000 instruments, 30,000 of which are HART devices. In addition, the refinery has somewhere between 3000 and 4000 HART valve positioners.
First, MOL connected all its HART devices through hardwired HART multiplexers to its various DCSs. Then the plant began to transition toward predictive maintenance and away from replacing all the valves when a shutdown occurred.
"You can see what has happened since we standardized on HART and Foundation fieldbus transmitters and began to enable HART valve positioners," Bereznai says. "We gather information before the turnaround using the HART diagnostic data and by doing this, we save between $20,000 and $70,000 per turnaround. So we are more predictive and proactive and less reactive." (Figure 1)
Bereznai continues, "If you look at Figure 2, you can see the breakdown of costed activities relating to valves. The costs are significantly higher without diagnostics than with HART diagnostics."
He adds, "We're replacing our analog positioners with HART, and we're experimenting with WirelessHART. We're in the early stages of using Emerson Process Management's THUM WirelessHART adapters to get diagnostic information out of HART devices without wiring them to multiplexers. We have 20 units in a test application."
He says his team also worried about EMI and other types of interference. So they conducted some nearly destructive testing. With the instrument live and broadcasting, they arc welded directly to the instrument housing, and found no detectable interference from the welding.
See Also: HART to the future!
Bereznai believes that the significant cost differential between wiring the diagnostics-laden HART cable to a new multiplexer and using the THUM adapters will mean that they can keep their existing devices longer.
Valve diagnostics are the most important thing, he believes. "There is a huge benefit. Predictive notification can save $7000 to $100,000 or more by avoiding unplanned outages. At our facility, our most important product is diesel. One day's diesel production is worth $300,000. In 2011, we avoided a one-day outage. You can see why this is important."
To make it work, Bereznai adds his team involved everyone. "Everybody needs asset management," he says, "and it's very important to involve everybody. There were many skeptics at first, but now they're believers."
How did Bereznai and his team get started? "First, we got high level buy in," he says. "Then we standardized on HART and later Foundation fieldbus devices. Then we put together a maintenance strategy plan and an action plan. We have a living contract with our three DCS vendors to maintain the systems and keep them current. And finally, we did training. Maintenance involves all the staff, and everybody does it."
Extracting diagnostic signals is one of the key use cases for wireless mesh networks in process plants. It would seem to be a no-brainer to jump in and start enabling wireless systems, but like MOL, most users are still doing pilot projects.
One of the reasons for this is the multiplicity (still) of wireless sensor network standards. WirelessHART, now IEC62591-WirelessHART, was the first IEC international standard, but it won't be the last. ISA100.11a will eventually be approved as a global standard, as will WIA-PA, the Chinese national standard.The ISA100.12 convergence process has been abandoned, and if end users buy some of each standard, they may actually be setting themselves up for unsafe practices and accidents. ISA100.11a devices do not interoperate with WirelessHART devices. They are not interchangeable with WirelessHART devices. And at this point, due to the failure of ISA100.12, there is no intention of making them either interchangeable or interoperable.
So what happens when a critical transmitter or wireless digital valve positioner fails during an important process condition like an upset? Somebody is detailed to run into the stores shed, get another transmitter, and go put it in . At 3 a.m., in upset conditions, it could be very easy to grab the transmitter that is not the one that is going to work in that application. This might cause an upset to become a disaster.
It isn't clear yet how much foothold WIA-PA will have, either inside or outside of China, but the other wireless mesh network standard, Zigbee, is making a substantial comeback.
Zigbee was investigated thoroughly by both the HART and ISA100 teams (they had many of the same members), and found not robust enough for the process industries. Unfortunately, the U.S. government decided that Zigbee would be a grand choice for the wireless sensor protocol for the Smart Grid.
Recently, several valve actuator and positioner indicator companies have decided to use Zigbee instead of WirelessHART. Even a SCADA company, exemys, headquartered in Argentina, but selling worldwide, has standardized on Zigbee for its substation and pumping station wireless mesh networks.
So even though MOL and others have shown that there are significant reasons to use wireless mesh networks, the end users remain skeptical.