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carletes (Chemical) (OP)
28 Jun 04 13:41
Dear all!! It is generally said that carbon steel parts can nor work at tempeartures higher than, approx. 800 F due to carbide phase may be converted to graphite, but I do not know the influence of time in that process, I mean, is there a minimum necesary time for that process to happen? That is to say, would it be allowable for a carbon steel to work over 800F during a short period of time? any recommmendation about this issue?

Thakns for any help.
unclesyd (Materials)
28 Jun 04 13:56
Come back with the type of steel, temperature the steel will see and the expected time of expsoure to that temperature.
This information is needed to give you a better answer to your question.
Metalguy (Materials)
28 Jun 04 14:35
Graphitization of carbon steels is generally requires a "long time"-either years or many months at 800 deg F.  If you are interested in short times, you should be OK.  Remember that the strength of CS gets pretty low at these temps., especially the YS.
davefitz (Mechanical)
28 Jun 04 14:52
The only problem with assuming the overheat occurs for only a short time is that in some applications, there is significant valve leakage and the pipe may actually operate in an overheat conditions for years.

Another technical issue is that some codes ( B31.1) do not permit one to overheat the pipe or vessel above the value for which the code provides an allowable stress, for any period of time.For most carbon steels, that means 800 F is not permitted ever.

Also, some states are now imposing required overheat trips based on max permitted operating temperature ( NC, for example).
YLWEA (Materials)
28 Jun 04 14:52
Also, note the increased susceptibility of weld HAZ to the problem.  If/when it occurs it will probably occur there first. I agree with unclesyd.  If you want to get quantitative then you need details, including steel composition.
PAN (Mechanical)
5 Jul 04 5:34
Refer to B16.5-1968, graphite formation for welded construction would be at 775 F.

As Metalguy's comment, short times will have no problem about graphitization in carbon steel.

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