Posted by Carl on April 09, 2000 at 09:44:15:
In Reply to: Materials of Boiler Construction posted by M Schmidt on March 28, 2000 at 10:16:46:
: I'm working on an industrial boiler design project and have noticed that most of the power boiler information I have found stops at 1050 F. I'd like to take the system to 1200 F. Does anyone know anything about this constraint? Is it strictly a materials issue, or are there other phenomena encountered above 1050 F in boilers?
Matt, There is the problem with creep in carbon steels at around 700F to 800F and around 1000F for austentic steels. However, there are some steels which can be used up to around 1500F. Thse generally are the very high alloy steel tube materials generally used only in the superheater areas of a generator. The lower limit of 1050 generally, and I mean generally are used in the generating banks where temperatures can reach around 1025 for heat inputs on water walls of boilers. You must also take into account that the very high alloy tubes would be cost factor many times more than carbon and low alloy tube materials. One source showes a cost per foot of length at 1150F an SA-213-T91 grade tube material at 23.00 a foot, and the next higher grade SA-213-TP 304H at over 40.00 per foot. These are compared to prices for low alloy and carbon down around 8.00 to 12.00 per foot. Hope this helps explain it. Another source would be to contact one of the boiler tube mnanufactures to get cost data in today's dollars. When you are desigining the cost vs life cycle of the plant is a weighty subject.
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