Revamps 2026 Issue

pair encoding the local speed of sound, and therefore the temperature, in its own segment of the waveguide. A single waveguide of one to two metres carries six to 12 independent temperature readings; the upper limit is set by the signal-to-noise ratio of higher-order reflections, not by the principle. The technology was developed at the Centre for Non-Destructive Evaluation, IIT Madras, and has been documented in the open literature.4 Two product variants of this technology were available for deployment. The first, μTMaps, is the process-side var - iant in which the waveguide is inserted into a thermowell or directly into the process stream, supporting service to 1,400°C. The second, μSTMaps, is the skin-temperature variant designed for retrofit onto the external surface of process tubes, furnaces, vessels, and reactors. The skin var - iant uses stainless-steel banding and a high-temperature thermal-coupling treatment, allowing installation during a planned shutdown without welding to pressure-containing components (see Figure 4 ). Compared with the conventional measurement chain on an SMR, the waveguide approach has three relevant attributes. Reading density per cable is one to two orders of magnitude higher: a TC requires one cable per measure - ment point, while a single waveguide bundle of fewer than 12 cables can deliver more than 200 independent points. Survivability in the radiant section is improved; field expe - rience to date has demonstrated continuous operation over 24 to 36 months in environments where weld-pad TCs fail in three to nine months. Calibration stability is different in nature: the measurement is based on geometry and mate - rial properties of the waveguide rather than on the Seebeck coefficient of an alloy junction, and the drift mechanisms are correspondingly different in magnitude and time scale. The acquisition unit converts the ultrasonic signals into 4-20 mA, Modbus TCP, or OPC-UA outputs and supports direct integration with the plant DCS, the process historian, and an industrial plant asset monitoring system (I-PAMS) for physics-based and AI-assisted soft sensing. Case study description The deployment was carried out on a 100,000 Nm³/h hydrogen plant supplying a hydrocracker train at a com - plex refinery in Asia. Specific identifiers have been withheld at the operator’s request, and certain numbers have been generalised without changing the technical conclusions.

Impact of temperature deviation on reformer tubes

+20˚C <50% reduced tube life

–20˚C 2% lost production

Temperature deviation directly impacts tube lifespan and process eciency

this measurement gap through retrofit of an ultrasonic mul - ti-point waveguide skin temperature sensor on 36 repre- sentative tubes, integrated continuously into the existing distributed control system (DCS). Technology overview The waveguide-based multi-point temperature sensor used in this deployment is built around a thin metallic waveguide installed in close thermal contact with the tube outer wall. A piezoelectric transducer at the cool end of the waveguide launches a guided ultrasonic pulse, which propagates along the waveguide and partially reflects from each of a sequence of engineered features (i.e., notches, bends, or diameter steps) at predetermined axial positions (see Figure 3 ). The time of flight between adjacent reflectors is a function of the speed of sound in that segment of the waveguide, which is in turn a calibrated function of the local temperature. In the single-point configuration (Figure 3 left), one heated segment S1 produces a single pair of reflected echoes (a/a′ and b/b′) at the transducer. In the multi-point configuration (Figure 3 right), additional engineered features along the waveguide create additional reflected echo pairs (c/c′), each Figure 2 Impact of tube wall temperature deviation on reformer tube life and hydrogen production. The asym - metric penalty drives the operational case for tighter, denser temperature data

Single point measurement

Multi-point measurement

Particle vibration

Straight waveguide

L(0,1)

Heating

Connector

Shear transducer

a a

b b

a a

b b

Amplitude (V)

Time (us)

Figure 3 Operating principle of single-point versus multi-point ultrasonic waveguide temperature measurement

Revamps 2026