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A flexible solution for process temperature measurement

Aug. 12, 2021

Nobody really wants to install a thermowell every time they need a process temperature measurement. Instead, wouldn’t it be a lot easier, and safer, to just measure the temperature at the surface of the pipe and extrapolate the process temperature from there? Problem is, there’s a lot of physics and calculations involved in that extrapolation. And because of those physics, not every application is well-suited to a non-invasive approach. The tricky part comes down to knowing which applications are which.

To gain a better understanding of the subtleties involved, Control caught up with Emerson's Zachary Massa, global product manager for Emerson's temperature transmitters portfolio. His responsibilities include the company’s Rosemount X-well non-invasive technology, which has been successfully applied to thousands of applications throughout the process industries since it was introduced to the process industries five years ago.

Q: Using a “skin” temperature measurement as proxy for the process temperature within a metal pipe certainly predates the introduction of X-well technology. What was it about X-well that really changed the game starting in 2016?

Zachary Massa

Global Product Manager, Temperature Transmitters, Emerson

www.emerson.com

A: In the past, skin temperature measurements couldn’t be relied on as accurate predictors of process temperature due to the impact of the environment and heat loss. The physics of heat transfer through the pipe needed to be considered, and variations in ambient conditions also had a significant impact on measurement accuracy. X-well technology first made it possible to model, in real-time, the physics of heat conduction through the pipe as well as compensate for variations in ambient temperature—and do all that within the transmitter itself.

X-well technology solutions are based on Emerson’s industry-leading Rosemount 3144P analog/HART and 648 wireless temperature transmitters. Notably, when intended for X-well use, the transmitter firmware comes factory configured with the pipe’s material of construction, diameter and schedule to accurately model heat flow from the process to the outer surface of the pipe. Meanwhile, the effects of changes in ambient temperature are compensated for based on the temperature reading of a second, high-accuracy RTD within the transmitter housing.

Our combination of non-invasive process temperature sensing combined with wireless connectivity remains unique in the industry.

Q: With a global installed base that now numbers in the thousands, what sorts of applications have you found most suitable for X-well technology?

A: Applications suitable for X-well technology range from monitoring pipelines to small line-size applications. Obviating the need for a thermowell is especially advantageous for pipes that require frequent cleaning, high velocity processes, slurries and heavy particulate fluids, clean-in-place processes, high viscosity fluids and harsh processes requiring exotic thermowell materials.

Retrofit or incremental temperature measurement applications are particularly attractive because no process penetration—or associated production interruption—is necessary. The value proposition of X-well technology in our wireless transmitters is even more compelling since you don’t need to run cables either. This makes it particularly useful for diagnostically driven implementations.

The elimination of thermowells also eliminates associated leak points and long-term maintenance requirements. From an engineering perspective, wake frequency calculations are eliminated, as is time spent determining material compatibility, correct insertion length and thermowell profile—resulting in a 65% savings in engineering time and effort.

Further, Rosemount X-well technology can be installed with standard pipe-clamp procedures and ordinary hand tools and does not require a welder or pipefitter, resulting in a 70% savings in installation costs. In any installation, at least half an inch of insulation over the skin sensor should always be used to meet performance expectations (see photo).

We continue to invest in and improve on the technology’s capabilities over time, but non-invasive methods in general aren’t suitable for processes with rapidly changing conditions, such as safety loops, custody transfer or fast control applications. Low fluid velocities and non-metallic pipes are also unsuitable. That being said, there are far more applications for which X-well technology is suitable than there are applications for which it isn’t.

Q: Say I’m an end user or system designer and want to gauge whether X-well technology is appropriate for a particular application. Are there tools available to help?

A: We can go a few steps further than simply determining whether X-well will work or not in a given application. Because we have a deep understanding of the underlying mathematics—as well as five years’ experience and thousands of applications under our belt—we can provide a definitive specification around total probable error (TPE). Dynamic processes are a bit more complex, but we can also calculate an effect on temperature response rate relative to a thermowell.

In short, we have proven results and the methodology to set clear expectations around non-invasive temperature measurement performance—and we're prepared to meet them, too.