Damage to Bourdon Tube Pressure Gauge

[Padmanapan]

Hello There,

I am using bourdon tube pressure gauge to measure vacuum. My set up consists of tube furnace with one end closed. The other end has a vacuum flange which is fitted with a pressure gauge. I am pumping in nitrogen +5% hydrogen and simultaneously pumping it out. The process is happening at around 700-850C at the heating zone of the tube furnace. The pressure gauge which is located on the end of the tube is way out of the heating zone but the end on which it is mounted is higher than room temperature. Now, the reading on the gauge is stuck somewhere around -0.5 MPa even when is set up is at atmospheric pressure. I am wondering what could be the reason for this malfunction. Is it due to 5%hydrogen that is being sucked out of the heating zone that is damaging the copper tube in bourdon setup or high temperature on the pressure gauge is melting the solder on the bourdon set up.
Lastly, can anyone suggest me some other types of gauge that can be used in this environment?

Thanks! everyone and really appreciate your help!

Padmanapan

 

[danw2]

Normal ambient temperature range limits for quality process pressure gauges is -40°F to +140°F (-40°C to +60°C). Wika's materials compatability chart recommends 316SS for hydrogen service.

I don't get -0.5 MegaPascals. It doesn't compute.

If the scale is kPa and you've got a -0.5kPa offset at atmosphere, then the zero is off because of the temperature. Accuracy and offset shifts with temperature. Re-zero it.

High, over spec heat levels will wear out and break the clock-work movements because of thermal expansion beyond spec limits.

Deadheaded pressure impulse tubing drops temperature quite rapidly. If there's more than a meter of tubing now, then it is likely from your description that the gauge is cooking from exposure to external radiant or convective heat, not from process heat in the tube.

You should extend the impulse pipe/line/tube and move the gauge to a location where radiant or convective heat won't kill it. You might need a shield (piece of sheet metal) to prevent radiant exposure. I wouldn't pay for seal and filled capillary when plain pipe extension can do the job.

Wika has a number of options for high temperature gauges, like filled finned impulse lines, but none of that will protect the gauge from over temp exposure from heat outside the process.

If, in fact, the heat was high enough to melt solder in a brass/copper internals, just changing to stainless steel with brazed internals will not help, it's still way too hot for a gauge to survive.

 

[Padmanapan]

Hi Dan,

Thanks for your input. Sorry for the confusion, it should have been 0.05MPa, instead of 0.5MPa. I will explore the options you have suggested.

Rgds,
Padmanapan