Thermowells lenght inside the pipe

can any one advice me what the recommended lenght of thermowell inside the pipe? and what is the relation between the lenght and velocity of the flow and the accuracy of measurement (the application is on gas plant)

Dear

You may purchase or get "ASME PTC 19.3" document for details or You may simply "Google" this document on internet.

Hope Your Problem will be Solve.

It used to be common practice to have the thermowell protrude half way across the pipe. I think that's OK up to about 6" but I don't see the point in going in more than 3".

It also depends on whats in the well, thermocouples are tip sensitive so only the end of the thermowell needs to be at process temperature wheras something like a bi-metal thermometer or filled system bulb has a much longer measuring element so it needs to be in further, about 2" for a Bi-metal.
Roy