Sometimes making one improvement leads to a jackpot of others.
For instance, Nucor Steel's plate mill in Tuscaloosa, Ala., recently needed a more reliable recording and reporting system to accurately monitor water resources used at the mill, but the existing reporting system wasn't reliable, its network connectivity was poor, and technical support was lacking.
As a result, Nucor Steel Tuscaloosa Inc. replaced its old, point-to-point wireless system in operation during 2009-13 with a new, mesh-based wireless solution. Also, rather than hiring an outside engineer or contractor, the plant's engineers and technicians found they could do almost all of the design and installation of their wireless replacement project on their own.
Well, the new mesh and WirelessHART solution not only provided more reliable reporting about the plant's water system, but it also delivered a cornucopia of other benefits to Nucor's operations. In fact, the new wireless system achieved so many gains that the Tuscaloosa mill has won the FieldComm Group 2014 Plant of the Year Award.
The present Tuscaloosa facility was built in 1985 on the site of what was once a paper mill. In 2004, Nucor Steel bought the mill and all of its assets from Corus, formerly British Steel.
The Tuscaloosa mill presently has about 430 employees, which Nucor calls "teammates," and operates 365 days a year. They convert scrap metal into 5.25-in. slab steel, which is then rolled out into 1/8-in. to 2-in. thick temper plate steel. They can also coil steel up to 1 in. thick. Steel from the mill is used for pipelines, building plate, tug boats, barges, and pressure vessels.
Ben Springer, environmental technician at Nucor Steel Tuscaloosa, reports the mill can produce more than 1.2 million tons of steel per year, so it also annually consumes a lot of industrial, non-potable water, which it gets at low pressure from Lake Tuscaloosa via the municipality. The mill sprays this water on its steel strand as it moves through the machines in its production line, both to help form the steel and to cool its equipment. This distribution system's water meters are monitored by transmitters that send back 4-20 mA signals via wireless to indicate flow rates and other parameters.
"The monitoring system is needed to see how much water is being used and where," says Springer. "By knowing this we can look for ways to conserve water and manage how we use the water in our process. We can also use the monitoring system as a troubleshooting aid if a failure of equipment or piping infrastructure occurred."
Migrating to mesh
To improve its water monitoring system, the Tuscaloosa team initially had to weigh several options, including continuing to invest in current wireless infrastructure, investigating alternate solutions such as manual collection of data, implementing a wired solution, or investigating an alternative wireless solution that better met their needs. A wired system wasn't an option because the location of the water meters would have require miles of excavation and new cables, a restricted number of analog cards in their PLCs, and limited flexibility for future applications.
However, the team's research found that WirelessHART was an open protocol, and they eventually selected it because it didn't require a radio frequency (RF) survey, it cost less than other options, and its devices offered a self-organizing mesh network, secure communications, easier deployment, simple system integration, multiple vendor options and total digital communications.
"The main goal was to monitor our water usage, and be able to troubleshoot it," says Springer. "We didn't have leaks yet, but if we did have an issue, we wanted to catch it quickly. This wouldn't be possible with the old wireless system because it was only about 60% reliable based on the many times it lost and dropped communications, the number of transient errors we were getting, and how often we had to work on it. We were dealing with wireless transmitter issues for several hours every week."
Design, install, succeed
Following some basic training on the wireless gateways, transmitters and support devices they planned to install, the Tuscaloosa team found they could do their wireless upgrade almost entirely in-house with some help from local sales representative Russell Poor. They deployed several wireless tools from Emerson Process Management, including Smart Wireless gateways/servers and Asset Management Suite (AMS) Wireless Snap-On planning software, which works with Google Maps (Figure 1).
These components use WirelessHART to communicate to four gateways, and their output is connected to seven radios from ProSoft Technology, which creates an IEEE 802.11 (WiFi) wireless backhaul network for communications from the gateways. The radios create their backhaul network to the PLCs, and the data can be access by using an OPC server application (Figure 2). This network receives input from 34 WirelessHART temperature transmitters, two WirelessHART temperature transmitters with extended range antennas, 19 WirelessHART dP transmitters, and one WirelessHART adapter connected to a wired HART device.
The four gateways presently cover 90% of the Tuscaloosa mill, and can easily go to 100% coverage if needed. The Prosoft radios are mounted 80-90 ft. up on the bag house, so no added towers were required.
Results attract cranes
Springer reports that the mill's new WirelessHART network achieved 100% data reliability that was on-time and validated. "It was much better than we expected," he says. "It's easy to get data out of the system. The WirelessHART signals go through buildings without any problems, and its meshing provides for a strong network with only a few routers needed, which help make the network even stronger. Depending on the application, we also saved 50-80% with WirelessHART compared to the costs of a wired system."
Beyond checking water use at the mill, the Tuscaloosa team discovered they could also use WirelessHART to monitor 19 dP transmitters in the plant's bag house and water filtration system. "When you melt steel, one of the byproducts is dust, and so the bag house is basically a large dust-collection system with big filter bags," explains Springer. "Measuring pressure drops in the bag house helps us determine when the bags need to be cleaned."
Next, these results began to draw interest from the mill's overhead crane maintenance team, who realized they could use WirelessHART to monitor bearing temperature and vibration. The crane moves steel in and out of the mill's production process, and also transports its ladle for casting and forming products.
Consequently, sensors and transmitters on the crane were added to the mill's WirelessHART-based network, where they deliver updates every 2-4 seconds. In the crane's gearbox/bearing monitoring application, savings were estimated at $150,000-$250,000 per event because now they can monitor the bearings, and take action before a major problem disables the crane.
"Because of WirelessHART's reliable and automated monitoring, we can now plan maintenance to our processes and equipment, rather than having unplanned shutdowns due to equipment failure," adds Springer. "We're now able to provide accurate and reliable data for the process points measured. WirelessHART is helping us reduce cost and prevent costly downtime."