If you have that high of temperature, I would assume the valve has an extended bonnet?
I would start w/ asking the manufacturer since they should have some information (they sized the extension). If that's a deadend, You could try to do some heat transfer equations based on the process temperature and ambient air temperature, but that'll just be a gross ballpark.
Go to the hardware store and buy a hand-held Laser Temperature Gage..
You hold it like a gun and point it at any part of the Valve and it will give you a very accurate reading. You do not have to be up close or even touch the object of interest. Just point and shoot!
Since I am now retired, I use my laser gun to check the temperature of my swimming pool water.
My Laser gun was made by RYOBI and was not expensive.
Sometimes its possible to do all the right things and still get bad results
Thank you for input, i don't have test set up to check practically high temp, is there anyway to theoretical way to determine temperature at Hand wheel.
