Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
(OP)
Hello all,
I am getting a refractory lined vessel fabricated for hydrogen service (reformed gas outlet header) and I am concerned that the refractory dry-out temperature and duration will cause material degradation to the 1.25Cr-0.5Mo shell (1100mm OD, 20mm thick).
The dry-out schedule states:
24 hour minimum curing
Heat up to 500 deg C at 25 deg/hour
Heat up to operatimg temperature (900 deg C) at 50 deg/hour.
Hold at 900 deg C for 6.6 hours minimum
Cool down at a maximum of 100 deg C/hour
Will this temperature and hold time at this temperature cause any material degradation? eg. spheroidisation, distortion, oxidation etc..
Thanks in advance for your help.
I am getting a refractory lined vessel fabricated for hydrogen service (reformed gas outlet header) and I am concerned that the refractory dry-out temperature and duration will cause material degradation to the 1.25Cr-0.5Mo shell (1100mm OD, 20mm thick).
The dry-out schedule states:
24 hour minimum curing
Heat up to 500 deg C at 25 deg/hour
Heat up to operatimg temperature (900 deg C) at 50 deg/hour.
Hold at 900 deg C for 6.6 hours minimum
Cool down at a maximum of 100 deg C/hour
Will this temperature and hold time at this temperature cause any material degradation? eg. spheroidisation, distortion, oxidation etc..
Thanks in advance for your help.





RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
I see no problem with the bake out and cure as you state. The time isn't long enough to do damage.
The only problem I've ever seen with a furnace cure was a slight collapse of the shell, but it was later determined that there could have been flame impingment on the shell. The shell was ok at the ends. If it is a furnace cure make sure everything is in order and operating properly, the same goes with portable heaters.
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
For our Fossil boilers that have the lower furnace lined with refractory up to several inches in thickness, the gas temperature to dry and cure the refractory is similar to your stated temperatures except the refractory protects the tube metal. We have the contractor install T/C’s and have never seen metal temperatures above 350 deg C for carbon steel boiler tubing. So in reality you should not see actual metal temperatures reach gas temperatures.
So to answer your question, I would say that the Grade 11 vessel material will not see any significant exposure to temperature that would seriously oxidize or spheroidize the metal provided the refractory has been correctly applied and cures under heat. The maximum metal temperature that I would allow for the vessel is 700 deg C to assure remaining safely below the lower critical transformation temperature.
I would suggest you have the contractor that is curing the refractory install T/C's to monitor curing temperature and metal temperature.
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
- Should we inspect hardness of shell material after dry-out?
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
Regarding hardness testing. Unless you exceed the lower critical transformation temperature of the vessel material - I would not bother with hardness testing.
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
What is the exact lower critical transformation temperature for 1.25Cr 0.5Mo? I have done a quick search on the internet but haven't been able to find it. Are you aware of any on-line refernces to this information for this and other materials?
Thanks again.
Cheers
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
The best on-line reference for materials information is ASM International. They have the entire ASM Handbook series available via Internet subscription for only $279 per year to members. Membership is only another $107 per year. You can obtain more information at:
http://www.asminternational.org
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
If you have access to ASME B31.1 Power Piping Code, the stated lower critical transformation temperature for !.25% Cr- 1/2% Mo alloy steel is 1430 deg F (775 deg C).
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
Not knowing what the make up is of the refractory that you are using, I would like to mention that a ramp up of 50C p/hr to a temp of 500C from ambient may cause major spalling and cracking and refractory falling off the walls of your work piece. I would recommend a "hold" temperature in your procedure of whatever amount of time it takes to remove any moisture. Somewhere around the 250F (farenheit) until steaming becomes lazy and not under any sort of pressure at the vent stack of your portable heatup.
Further,, have your contractor install the TC's between the shell of your vessel and the refractory, I personally install them at the lower portion of the refractory as well as in the middle and near the top. As well, on the surface of your refractory. Control is the Key word in dryouts, the more TC's you have, the more control you have with the portable burners and fans.
Just my 2 cents
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
Cheers
RE: Heating 1.25Cr-0.5Mo to 900 deg C for 6.6 hours
This may not be an issue in the refractory-lined areas, but may come into play where the metal is exposed (if it is at all).
Just some food for thought...
~NiM