Use of heater pipe St 35.8 (1.0305) at 800¦C, what is maximal pressure

[kapot]

A heater in a heater pipe is used to heat compressed air to 400°C. However it is possible that the heater does not turn off at 400°C and it can reach up to 800-900°C. In this case, the design requests the heater must fail before the heater pipe fails. As the heater pipe is constructed of St35.8 (1.0305) my question is: what is the maximal pressure the heater pipe can whitstand at this elevated temperature? It has to be mentionned that the time at this elevated temperature is not that long (in terms of hours). We did already some tests and a pressure of 11 bar seemed okay.

 

[metengr]

kapot;
St35.8 is low carbon steel seamless tube/pipe. At 800 deg C you are in the austenitic phase region meaning this material has a tensile strength values that is less than 10% of the room temperature value (use the hoop stress formula and determine the pressure).

It will creep and fail within a very short time (hours) from stress rupture. This means do NOT use at this temperature.