Selection of thermocouples for high-temperature hydrogen environments
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Dear experts, I would like to ask: in a sealed environment, at low temperatures the air in that space is gradually replaced by nitrogen, and the temperature is raised to 300 degrees; then hydrogen is used to replace the nitrogen gradually, with the temperature being increased to 900 degrees. Finally, nitrogen replaces hydrogen again and the temperature is lowered. For such operating conditions, various types of protective tube materials should be used; should K or S be chosen? Some manuals state that k cannot be used with reducing gases, but I have a protective tube; should choosing the right material for that tube be sufficient? I would also appreciate some guidance from the experts.
This post was last edited by “Hasty Passerby” on January 3, 2018, at 21:57. Based on the temperature range, it seems appropriate to choose the K thermocouple type. Using corundum material for the protective tube should be fine; however, the insertion length shouldn’t be too long, as its strength might be insufficient at high temperatures. It’s advisable to discuss this in detail with the manufacturer. In a hydrogen environment, the components are separated by protective tubes, which ensures that their lifespan is not too short; sometimes manufacturers opt for double-layer protective tubes.
This post was last edited by huio1983 on 2018-1-4 09:44. What is the work pressure? The double-tube design needs to be taken into account； The day before yesterday, someone posted something similar about a cooling acidic atmosphere. If the temperature is not high, metals can be considered
Try using a double-layer sleeve with outer metal (GH3039) and inner corundum
Choosing the K type is sufficient; however, if the casing material is to be metal, it is necessary to use one that can resist hydrogen embrittlement under high temperatures and pressures, and such a material should have a low carbon content along with the addition of special elements.
Corundum is probably not suitable, as the measuring tip can easily get damaged during equipment maintenance. Judging from what the seniors think, double-layer casings should be given priority consideration; after all, it’s not a scenario involving rapid temperature changes, so some measurement delay is acceptable.
The pressure is not high; it is a positive-pressure environment of around 10 kPa.
The pressure is not high. For a previous project, I used the metal Incoloy 600, but there were frequent issues with the thermocouple signals; the manufacturer said it was due to instability in the internal welding. I’ve always wondered how hydrogen has an effect.
I’m here too to see what good methods the experts have, so I can learn a bit from them
The pressure isn’t high; what’s the maximum temperature possible? If the temperature exceeds 1000 degrees Celsius, it’s better to use S. However, it’s not clear whether ceramic protective tubes can be used in a hydrogen environment; be careful not to touch them during maintenance. Hydrogen has a very low molecular weight, so the welding quality must be high.