Thermowell Selection and Application - Burns …

1 Thermowell Selection and Application If you are experiencing audio problems please call the teleconference number below 1-408-600-3600. Access code 660 637 935. Bill Bergquist, Sr. applications Engineer Bill Jeff Wigen, National Account Manager Jeff Burns Engineering Thermowell Selection and Application What We'll Cover 2. The Thermowell used with your temperature sensor provides critical protection, access, and measurement integrity. We'll shed some light on how, why, and when to apply this important device. Thermowell basics Purpose Types Process connection styles Materials, coatings and surface finish Performance Wake frequency & strength Immersion length Time response Custom designs Specifying Definitions/codes Typical drawing Details Testing & certifications Options Preventive Maintenance Selection Checklist Burns Engineering Thermowell Selection and Application A Thermowell 's main purpose is to protect the Thermowell Basics - Purpose 3.

2 Temperature sensor to insure long life and Why use a Thermowell ? accurate measurement. Maintenance is aided by Protect the temperature sensor from: allowing the sensor to be removed without Excessive pressures having to drain the pipe or tank. Sensor changes Excessive material velocities & viscosities Corrosion can be done on the fly. Erosion Simplify maintenance Sensor replacement without draining the system Eliminate potential for contamination system stays closed Protection increases potential life of the sensor Improve temperature measurements Burns Engineering Thermowell Selection and Application Thermowell types are designated by the style of Thermowell Basics - Types 4. stem or wetted portion of the well.

3 Protection Thermowell types tubes are typically used for thermocouples and Stepped are not suited for use with RTDs because they do Tapered not provide enough support for the sensor. Straight Sanitary Most thermowells are machined from bar stock Protection tube to insure integrity for high pressure applications . Typically made from pipe Flanges are joined to a Thermowell stem most Usually not suited for RTDs commonly by a welding process. Smaller wells may be constructed from tubing and have the end welded closed and a process connection welded on. These are typically used in low pressure applications . Burns Engineering Thermowell Selection and Application Stepped, sometimes referred to as reduced tip, Thermowell Basics - Stem Types 5.

4 Wells are usually diameter and step down to diameter to improve time response. Tapered wells are a balance between strength and time response. Straight wells are specified where Stepped increased life is desired due to corrosion or erosion. Tapered Straight Burns Engineering Thermowell Selection and Application Connections to the process are accomplished Thermowell Basics - Process Connections 6. with tapered pipe threads or adaptations of pipe Connection styles or sanitary tubing flange connections. A blank or Flange blind flange is modified to accept the Thermowell ANSI stem and then easily attaches to standard Van Stone flanges. Socket weld Weld-in Weld in styles are used for convenience or where Threaded Sanitary flange exposed threads may collect contaminants such O-Ring as in food processing or pharmaceutical production.

5 A specialty type of connection incorporates an O . Burns Engineering Thermowell Selection and Application ring to seal inside a sleeve welded to a tank. Sometimes referred to as an Ingold fitting after the company that invented it for ph and oxygen sensors. These are just a few of the several styles Thermowell Basics - Process Connections 7. available. Any imaginable pipe or tubing connection style either has been or could be adapted to a Thermowell process connection. Burns Engineering Thermowell Selection and Application A sanitary weld in style such as this one is used in Sanitary Weld-In 8. sanitary process tanks where cracks and crevices are not desired. Burns Engineering Thermowell Selection and Application This is a Thermowell with a sanitary flange Sanitary Flange 9.

6 Connection which is sometimes referred to as a Tri Clamp connector. It is the most common style of sanitary connection. The high polish and large radius between stem and flange improve corrosion resistance and make cleaning easier. Burns Engineering Thermowell Selection and Application Another style of sanitary well uses a sanitary Sanitary with Process & Instrument Flange 10. flange for attachment of the temperature sensor. Burns Engineering Thermowell Selection and Application Sanitary Process and Instrument Flange 11. Burns Engineering Thermowell Selection and Application No tools are required to install or remove the Sanitary Easy Access Tri-Clamp 12. sensor which makes for easier maintenance. Burns Engineering Thermowell Selection and Application The most common style of instrument O-Ring 13.

7 Connection is a NPT female thread as shown here on this O ring style well. This style well installs into a sleeve welded to a tank which accepts the well and the threaded nut holds it in place. A tight fit insures that the O ring seals securely. Burns Engineering Thermowell Selection and Application When selecting a process connection there are Thermowell Basics - Process Connections 14. several things to consider. Threaded connections Process connection Selection are the easiest, flange connection require a Thread size flange size, pressure rating, and gasket surface Typically tapered pipe thread style. Flange size and rating Lag length is an extension of the non wetted Gasket surface type Raised portion of the well to reach through insulation or Flat other obstacles to provide wrench access.

8 RTJ. Typically specified for threaded wells. Lag length Added Thermowell length outside process to reach through Test wells that sit empty for long periods of time insulation should have a plug in the instrument connection Brass or SS plug for test wells to prevent debris from entering. Burns Engineering Thermowell Selection and Application Material Selection can be as simple as choosing Materials 15. the same material as the tank or pipe where it is Factors to consider to be installed. This works most of the time but Define the conditions there are exceptions. In the case of corrosion or Corrosion/erosion erosion an object placed into a flow is more Temperature susceptible to those effects and a different Pressure Fluid Properties material will be necessary to provide longer life.

9 Match the pipe or tank materials There are corrosion charts available from Refer to corrosion charts Thermowell manufacturers that list the preferred material for chemicals at different conditions. Burns Engineering Thermowell Selection and Application Material Selection tables are available for Materials Corrosion 16. numerous chemicals and conditions. Note that concentration and temperature have an Chemical Condition Material influence on the recommended material. The higher the temperature and/or concentration the more corrosive the chemical can be. Burns Engineering Thermowell Selection and Application Choosing the wrong material can result in failure Corrosion 17. of the well. Here the tip has corroded away and allowed the process fluid to leak inside the well.

10 Photo courtesy of Alloy Engineering Burns Engineering Thermowell Selection and Application This is a view inside the tip section showing Corrosion 18. corrosion on the inside from the leaking process fluid. Photo courtesy of Alloy Engineering Burns Engineering Thermowell Selection and Application Particles suspended in a fluid or powdered Materials - Erosion 19. materials can cause erosion of the well over Materials time. There are several materials available to Cobalt-Chromium (Stellite ) Silicon Carbide (Hexoloy ). Cobalt-Nickel (Wallex ) Alumina slow down the erosion. Most are hard materials Tungsten Carbide Photo courtesy of Lisa Danielson that are applied through a welding or spraying process.