Thermowells in Hydrogen Service

Would you mind explaining, please, where this hydrogen is coming from?

In low pressure furnaces and retorts, excess hydrogen is burned in an open flame. A ceramic glow-bar is often used to reignite the flame if it goes out.

You still need to describe what the use is. Purging has nothing to do with 'green rot' and will not help.

The thermowells are to be installed in 99+% H2 lines at pressures of 300 to 1200 psig @200 to 800 degF for Hydrotreater and Pressure Swing Adsorption services.

The temperature is low - no problem there. İf you are using a 'good' factory bought thermowell İ can not understand how you get H2 into the thermowell. Even H2 will not diffuse through the wall of a solid metal TC. Venting would only guarantee you have a fire in the event of a leak. At 80 barg that would be fun! İ expect the weep hole you are talking about is for pressure equalization between the interior of the thermowell and ambient.

I would obtain a thermowell with a low diffusion coefficient for H2. But, if you can't get one, then a vent hole with a glow-bar to burn off the H2 may be a good idea.

İ operated plants where we had H2 at 1000 degrees C though at low pressure 8000 plus hours per year. Difussion of the H2 through the thremowell (inconell 600) was not a problem. İf you do have an H2 leak and you are in a vented location it is preferable if it does not burn as it rises and goes away.

"Goes away" is not an acceptable term to safety engineers. Plants have exploded because people thought the H2 "went away". I agree that diffusion through one thermowell may not be cause for concern, but I don't know how many thermowells are involved and if there are other sources of H2. I suggest OP check things out and if there is any doubt, burn the excess gas.

Work with the gas for 30 years and then tell me about it please. İn a plant İ manage no one would ever burn off H2 in that manner. The plants have exploded statement is sensational but is a nonsense statement. Many things in this world İ don't know much about - handling hydrogen is one area İ know very well.

In the Northeast US I have been involved in a few H2 mishaps. I have seen a factory that exploded. The roof had been designed (by code) to blow off, and it functioned as intended. I also have been in the middle of two H2 explosions and while frightening, they did no lasting damage. Most of the factories I have inspected that operate H2 belt furnaces at slightly over 1 atm, burn off the excess H2 as I described. It is common practice.