Failure of temperature sensors for boiler bed

[SA07]

Hi
We have recurrent failure of 9 temperature sensors in our boiler bed. In the boiler, coal ash and bottom ash are burnt. We have type K thermocouple. Can you plz confirm what sensor type & material we should use? Also the type of material for the thermowell? Operating temperature is below:


Operating temp
/deg C
975-1000 deg C


Max process
temp/Deg C
1070 deg C

 

[TugboatEng]

Type S, Inconel.

 

[IRstuff]

https://www.thermocoupleinfo.com/thermocouple-types.htm[/URL]]Type B Thermocouple (Platinum Rhodium – 30% / Platinum Rhodium – 6%) Temperature Range: Thermocouple grade wire, 32 to 3100F (0 to 1700C)
Type R Thermocouple (Platinum Rhodium -13% / Platinum) Temperature Range: Thermocouple grade wire, -58 to 2700F (-50 to 1480C)
Type S Thermocouple (Platinum Rhodium - 10% / Platinum) Temperature Range: Thermocouple Grade Wire Maximum continuous operating temperature: up to 2,912F (1600C)

How long did they work, if ever? Are you sure you didn't have a massive overtemperature event?
What do your temperature logs say?

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[RedSnake]

It's seems you are pretty close at max with a type K especially if you don't have the right wire gage.
_____________________________________________________________________________________________________________
Type K Thermocouple (Nickel-Chromium / Nickel-Alumel): The type K is the most common type of thermocouple.
It’s inexpensive, accurate, reliable, and has a wide temperature range.
The type K is commonly found in nuclear applications because of its relative radiation hardness.
Maximum continuous temperature is around 1,100C.
_____________________________________________________________________________________________________________
Temperature Ranges for Type K Thermocouples
Type K thermocouples have a general temperature range of -200 to 1260°C (-326 to 2300°F), however there are some caveats to this:

If used for temperatures below 0°C special material is needed in order to meet the specified accuracies. Also, Special Limits of Error are not specified for temperatures below 0°C.
The ultimate suggested upper temperature limits for Type K are based on the size of the conductor used:
Wire Gage Diameter Maximum Suggested Temperature
#8 AWG 0.128” 1280°C/2300°F
#14 AWG 0.064” 1090°C/2000°F
#20 AWG 0.032” 980°C/1800°F
#24 AWG 0.020” 870°C/1600°F
#28 AWG 0.013” 870°C/1600°F
#30 AWG 0.010” 760°C/1400°F

Best regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[EdStainless]

Type K have horrific temp drift issues, Type N would be an option other than the Pt alloys.
An alloy 600 thermowell should be satisfactory and they are common.

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P.E. Metallurgy, consulting work welcomed