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BP Takes Measure of Wireless, Clamp-on Temperature Sensor

To install an X-well, clean the pipe surface, clamp it on and insulate it. A general contractor can do it with basic tools. In fact, the most time-consuming part of the installation was the time it took to get a contractor to remove the insulation from the pipe.” Roger Goecke, reliability instrument and safety system engineer, BP Cherry Point Refinery, Blaine, Washington, spoke at the 2017 Emerson Global Users Exchange.

To add a temperature sensor to an existing pipe using a thermowell, you have to cut into the pipe and weld in a nozzle. It may require scaffold work, and always calls for a thorough engineering analysis. “We wanted to explore the idea of not having to put in expensive thermowells and nozzles to do temperature measurements, so we did a pilot project,” said Roger Goecke, reliability instrument and safety system engineer, BP Cherry Point Refinery, Blaine, Washington. The refinery opened in 1971 and has a capacity of 234,000 bbl/day, with 90% of production being transportation fuel. The pilot project placed one of Emerson’s Rosemount X-well clamp-on, wireless transmitters on a pipe near an existing control thermocouple in a thermowell, and evaluated its performance by comparing it to the thermocouple.

“To install an X-well, clean the pipe surface, clamp it on and insulate it,” said Goecke. “A general contractor can do it with basic tools. In fact, the most time-consuming part of the installation was the time it took to get a contractor to remove the insulation from the pipe.”

An X-well measures the temperature inside the pipe without intrusion. “It solves a thermodynamic equation with temperature compensation, allowing for heat dissipation,” said Marco Donnangelo, global business development manager, Emerson Automation Solutions. “It considers the whole equation, using information about the process pipe.

“Specifying a thermowell requires nine design inputs. For an X-well, we just need three—pipe diameter, material and schedule (wall thickness).”

The application is on a diesel stripper tower feedline where reactor feed effluent at about 450 °F goes to a feed drum, then to the stripper. “It’s an 8-in. schedule standard ASTM A106GRB pipe,” Goecke said. “We sanded it to bare steel, clamped the sensor on, and insulated it with two inches of soft-pack and silicone.”

The X-well can be fitted to pipes from one-half to 48 inches in diameter, making it suitable for small-diameter pipes where a thermowell is impractical. Mounting clamps are available in carbon steel and in 304, 316 and duplex stainless steels to match the pope material and minimize corrosion issues.

Accuracy more than adequate

The installation was first tested uninsulated, and results were erratic and erroneous. “The pipe must be insulated for at least six inches to either side of the sensor, and the insulation must extend up the sensor neck to the transmitter, but not cover the ambient air temperature sensor,” said Donnangelo. The insulation must be at least half an inch thick, and more is better.

On horizontal pipes with liquid, it’s better to mount it on the bottom of the pipe to be sure the liquid is contacting the wall when the pipe is not full. Internal pipe corrosion or lined pipes can affect pipe thickness and thermal conductivity, which can be compensated in the software.

Trials were run short- and long-term, comparing the X-well (RTD) to the control thermocouple (Type K) installed in the nearby well. In the short-term trial, “X-well averaged 4.96 °F cooler than the control thermocouple over the temperature range of 446.5 °F to 485 °F,” said Stephen Reeves, executive sales representative with Emerson’s Rosemount measurement technologies. The long-term test extended over season changes with ambient temperatures from 30 °F to 90 °F with “the same results,” he added.

The response time is “good, but not as fast as an embedded thermocouple,” Reeves said, which may limit its use in dynamic applications. Also, “you have to consider the latency of the wireless network.” The Cherry Point Refinery has a robust wireless infrastructure, and latency was not an issue for this application.

Now, new temperature monitoring points can be installed when needed rather than waiting for a shutdown. The combination of wireless and non-intrusive technology makes for a high-value, rapid-deployment option. “Based on the results of the pilot, we can see making more applications on relatively low-temperature, non-alarm applications—the plant has a policy prohibiting alarms on wireless,” said Goecke. One of those applications is in the tank farm, to reduce the need for trips outside to check temperatures.