INNOVATION AT OMC

Tube Skin Thermocouples

OMC’s unique range of tube skin thermocouples for process heaters offers higher accuracy and reliability over competing thermocouples.

Due to its unique 8mm diameter sheath made from Hastelloy-X, the ‘Fan Tip’ tube skin thermocouple can be bent and coiled to enable movement in both the horizontal and vertical axes. The 40mm end tip of the thermocouple can be welded to the heater tubes on both sides, which significantly reduces the chances of the thermocouple breaking off whilst in service. The Fan Tip tube skin thermocouple has a novel fanshaped head that enables it to be easily welded to any type of process heater tube. This means the user gets a more accurate temperature measurement on the surface of the tube. Construction and tip profile accuracy is now between +4 and +6 oC of the true tube temperature.

Currently used by BP, Esso, Exxon Mobil and STATOIL, the Fan Tip thermocouple is ideal for any process burning or heating applications, including hazardous area oil and gas, chemical and petrochemical installations.

The Fan Tip is suitable for gas-fired, light fuel oil and heavy fuel oil heaters. The sheath can be supplied in either 316 stainless steel for gas-fired heaters, Hastelloy-X for light fuel oil, or dual sheath AR-161 version for arduous, heavy fuel oil applications. The length of the sheath can be increased by up to 30 metres. The sheath can be bent in a cold state to meet any fixture and exit point on the heater tube.

The VortexWell Thermowell

Up to now, if a thermowell failed the ASME Performance Test Code (PTC 19.3, 2004), the manufacturer has been left with several options: either to shorten the thermowell immersion, or to increase the diameter of the thermowell, neither of which are often very practical or cost effective for the user. The only other option used by the majority of thermowell suppliers is to incorporate a velocity collar on the thermowell in order to move the point of vibration or resonance.

After extensive R&D and independent evaluation, OMC has developed a unique design of thermowell, the VortexWell®, which doesn’t require a velocity collar and is cost effective for the end user in terms of purchase, installation and maintenance costs (whole lifecycle costs).

VortexWell® incorporates an innovative helical strake design, very similar to the helical strakes seen on car aerials and cooling towers. By using the latest CFD software to visualise the flow behaviour, OMC was able to accurately compare a standard tapered thermowell and its new VortexWell®. In the analyses, the standard tapered thermowell showed classic shedding behaviour as expected, whereas the VortexWell® demonstrated no signs of regular flow behaviour. The VortexWell® helical strake design disturbed the flow sufficiently to interrupt the regular formation of vortices. Whilst a small vortex was observed in the wake of the VortexWell® this was a localised stagnation point and didn’t shed.