The fundamental constraint on conventional UT inspection is temperature. Standard piezoelectric transducers and standard couplants have operational limits of approximately 50–60°C — limiting conventional inspection to shutdown assets that have been cooled to near-ambient temperature. For refineries, chemical plants, power stations, and process facilities where continuous operation is the commercial imperative, this constraint defines the inspection interval: you can only inspect what you can cool, and you can only cool what you can shut down.
High Temperature UT Capability
Sustained Contact at Operating Temperature
Our high-temperature UT systems use delay line probes, buffer rod
probes, and piezocomposite high-temperature elements specifically engineered
for sustained contact with surfaces operating at temperatures up to 550°C. The
transducer design maintains acoustic performance at temperature — not just
brief contact tolerance — enabling repeated measurements and scanning at a
defined monitoring location over the duration of the inspection deployment.
Acoustic Velocity Correction
Ultrasonic velocity in steel decreases with increasing temperature. At
500°C, the acoustic velocity in carbon steel is approximately 10% lower than at
ambient temperature — introducing a proportional error in thickness measurement
if uncorrected. Our high-temperature UT systems apply real-time acoustic
velocity correction based on the measured surface temperature at each
inspection point, ensuring that reported thickness values are accurate at the
actual operating temperature rather than calibrated for ambient conditions.
Corrosion Mapping at Temperature
Where a single-point thickness measurement identifies a zone of concern,
high-temperature corrosion mapping provides the spatial context — a C-scan
image of wall thickness distribution across the area surrounding the
measurement point. Robotic arm or manually guided encoded scanning systems are
deployed to produce 2D and 3D thickness maps at operating temperature, enabling
the spatial distribution of corrosion to be characterised without waiting for a
planned shutdown.
Permanent Sensor Installation
For critical monitoring locations — known corrosion hotspots, high-flow
erosion zones, or areas of previous significant metal loss — permanently
installed high-temperature UT sensors enable continuous or scheduled automated
readings without repeated manual access. Sensor arrays are connected to data
acquisition systems that trend readings over time and alert on rate changes
between scheduled reads.
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Refinery fired heater tube thickness monitoring in
service
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Pressure vessel shell monitoring during hot standby
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Steam drum and boiler wall thickness monitoring
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Reformer and reactor pressure part thickness monitoring
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Catalytic cracker (FCCU) hot wall monitoring
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Glass furnace steel shell inspection at operating
temperature
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Chemical reactor and autoclave thickness monitoring
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Cement kiln shell monitoring
High-temperature UT inspections are conducted with velocity-corrected
calibration at the nominal inspection surface temperature. Calibration blocks
of the same material specification as the asset are maintained at temperature
and used for calibration before and after each inspection session. Procedures
are developed in accordance with ASME Section V Article 23 (SE-797 High Temperature
UT) and applicable client or operator specifications.