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Teflon

Application Guide catalog - 7347 Application Guide

The Art of TemperatureSensing

Material Selection Thermowell Manu-facturing Standards and MaterialSelection Guide In selecting a thermowell or protectingtube, the first thing to do is determinethe nature of the environment and what material will best resist its destructiveeffects. To select the appropriate material, see Watlow’s Temperature Sensing Solutions Catalog, pages 127-131, for

Thermowells and Protecting Tubes

.The guide will help you determine whatmaterial will best meet your protectionrequirements. Please note that it’s not just the corrosive agent, but also itstemperature. Temperature can have a significant effect on how a material willhold up in actual conditions.Measuring a substance that’s flowingis another consideration. In this case, you need to determine the fluid’s vis-cosity at the process operating tem- perature and combine that factor with its flow rate to determine the amount of lateral (shear) force it will exert onthe face of the thermowell or protect-ing tube. Once the total shear force is figured, you must then be sure the size, shape and material will hold up. Don’t forget to include the effects oferosion if the fluid has abrasiveparticulate material. Using thermowells and protectingtubes will isolate a sensor from hostileenvironments that could adverselyaffect its operation or life.Thermowells are machined from solidbar stock and come in a wide varietyof metals and alloys.Protecting tubes are made up fromparts, either metallic or non-metallic materials, generally ceramics. See Watlow TemperatureSensing Solutions, Temperature Sensors, Wire and Cable catalog for: •Thermowell MaterialSelection Guide•Ceramic and Silicon-Carbide Protecting TubeApplication Data•Typical Physical Data forProtecting Tubes•Physical Properties ofHexoloy
® Coatings If the thermal mass of a thermowell orprotecting tube slows response to an unacceptable level, Teflon
® coatingsmay provide a solution. Possessing a high resistance to many corrosive agents, Teflon
® coating can protect alow-mass probe that would otherwisebe damaged in a hostile environment. Such applications include electro-plating and anodizing baths, andmany common acids like sulfuric, hydrochloric, nitric and chromic.
® Materials—Technical Data
® is a registered trademark of Carborundum Company. Teflon ® is a registered trademark of E.I. du Pont de Nemours & Company.Hexoloy 48