Pipe Thread Size for Thermowells

Thermowells can usually be obtained in pipe thread sizes of 1/2-inch as a special type, while 3/4-inch and 1-inch are the usual available stock sizes and the 1-1/4-inch is a special size. 

Thermowells in the 1/2-inch size are used where space on the equipment will only allow a 1/2-inch connection to be made for either a thermometer or thermocouple assembly. 

The 3/4-inch thermowell is generally selected where process operating service pressures and temperatures are in the low range. It is used for mounting a thermometer or thermobulb in a thermowell and for thermocouple assemblies. This size is a few dollars cheaper than the next larger one. 

When a 3/4-inch thermowell is to be used, the pipe designer is cautioned not to use the conventional 3/4-inch full pipe coupling for mounting it. If the 3/4-inch full coupling is welded on equipment, the narrowness of the inside of the coupling where the two pipe threads meet may prevent thermowell insertion. If, instead, a 3/4-inch, 6,000-pound thread adapter or elbow 

It is customary, when the piping and vessels are of carbon steel, to order the thermowells in 

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