A thermowell is a simple component used in the process industry to protect devices such as thermocouples, thermometers and thermistors. It acts as a barrier between the medium and the sensing element of the device. The medium transfers heat to the wall of the thermowell which in turn transfers heat to the sensor whilst protecting it from corrosive, abrasive materials.
Thermowells are either machined from bar stock or fabricated welded and there are three main varieties: straight, stepped and tapered. As its name suggests a straight thermowell is a long and straight tube with a consistent diameter, they are generally considered to be more corrosion resistant and used in lower frequency applications. Stepped thermowells get smaller in diameter as they go down from ¾” to ½” and are better suited for dealing with a medium that is likely to experience rapid temperature changes. Tapered thermowells have a gradually decreasing diameter from base to tip. They provide a greater strength to weight ratio and so are used in applications with higher vibrations and higher fluid velocities.
In order to fit to the device they are protecting, themowells come in a number of connecting styles with the most common being Threaded, which is best suited for smaller diameter devices that aren’t changed as frequently. Flanged which is best suited to larger pipes and higher corrosion rates and more frequent replacement. Welded is the best option for non-corrosive environments where replacement isn’t needed.
Thermowells are made out of a number of materials including carbon and stainless steels, brass and inconel depending on their application and the medium they are likely to come into contact with.
In extreme environments, thermowells may need additional protection in order to prolong their lifespan and so many are protected through the use of super alloy coating applied through thermal spraying. The most common of these is Stellite.
Stellite is a range of cobalt-chromium alloys which are all designed for high wear, high corrosion and high temperature applications. Stellite is often applied through welding but for smaller components such as those found in a thermowell this would cause distortion and so thermal spraying has become the process of choice to apply Stellite and other materials such as Tungsten Carbide and Aluminium Oxide. Where you have a more extreme environment then thermally sprayed coating can certainly extend the part life on your thermowell.
What We Offer
B&B Precision can machine and coat bespoke thermowells for your applications. With CNC machines, HVOF coating and our own metallurgical laboratory all under one roof we can quickly and efficiently produce components to your drawing. We are fully ISO certified and deliver across the UK.