Non-invasive temperature sensors come of age

Temperature sensing is one of the most widely measured parameters in industrial processes. Whether a process relates to chemicals, oil & gas, low carbon, or other industries, continuous temperature sensing is crucial in terms of controlling reactions, maintaining product quality, ensuring safety, and preventing equipment damage. But to obtain meaningful results, measurements need to be taken in as many locations as possible. And that is expensive and complicated.

Until now, many industrial processes have relied on thermowells. These devices are comprised of a sheath or sleeve that protects a temperature sensor from potentially damaging conditions, such as pressure, corrosive chemicals, or high and/or variable flow rates. However, thermowells are not without their limitations. Drilling a hole into a pressurized live pipe is a recipe for disaster, meaning that thermowell installation must take place while operations are paused. Once in place, constant exposure to fluids that can be abrasive and moving at high speeds can cause wear and tear, which in turn results in sensor replacement and more shutdowns.

Many of these challenges have now been addressed thanks to developments in physics models and innovative surface mounted technologies, such as ABB’s NINVA™ non-invasive temperature sensor, which can turn any piece of metal piping carrying a fluid into an accurate and responsive temperature measurement point. NINVA’s non-invasive measurement approach first predicts how the surface temperature of a pipe differs from its process temperature. Then the device, which is built around ABB’s proven TTH300 transmitter and a pair of temperature sensors, compensates for errors from surface sensors, such as ambient and contact effects, to accurately capture the pipe’s true surface temperature. Supported by the HART 7 communication protocol, NINVA is the first clamp-on non-invasive temperature sensor that has been fully assessed to the IEC61508 standard and meets the requirements for SIL2, meaning that it can be easily integrated into the vast majority of process facilities.

By using measurements derived from the surface temperature of a pipe, NINVA eliminates the need to drill into the pipe, thus greatly reducing the complexity, time and cost associated with creating new measurement points – and without compromising the accuracy or response times provided by existing thermowells.

The challenge for surface-mounted devices has always been to provide a level of reliability that industrial users can rely on despite erratic ambient temperatures and potential installation errors, recognizing that for many applications temperature measurement accuracy is paramount.

The answer to these issues is NINVA’s twin-sensor design. One sensor is in contact with the surface of the pipe, while the other measures the ambient temperature conditions in the immediate vicinity. The data produced is then fed into software that compensates for contact resistances and ambient effects to accurately calculate the surface temperature of a pipe or structure.

When combined with data from process models that predict the temperature behavior of liquids or liquid-like mediums flowing in turbulent regimes in metal pipes, NINVA’s measurements provide a level of performance that  is comparable with that of traditional invasive devices but is measurably safer, simpler and more cost effective.

Furthermore, thanks to the easy-fit nature of the sensor, installation-related savings can be as great as 75 percent compared with thermowells. The use of a two-clamp collar allows the sensors to be attached without penetrating the pipeline. The amount of insulation required is also reduced, with just the foot of the device needing to be covered. As a result, a sensor can usually be installed in under an hour.

The latest generation of NINVA sensors benefits from easy setup with push-button programming that can eliminate the need for a service engineer visit when calibration is required. All told, the sensors have been proven as a viable alternative to thermowells in hundreds of customer applications in the chemical and oil & gas sectors.

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