I am looking into options for breeching and chimney lining for condensing boilers. The manufacturer calls for AL29-4C stainless, apparently other grades of stainless have failed due to corrosion at the welded joints. I was advised by another boiler rep today that Al294C can not be formed or welded in the field due to a very low carbon content. This would rule out fabrication of a rectangular chimney liner. Has anyone had experience with this material?
I found this on the Allegheny Ludlum website- AL29-4C is apparently a copyrighted designation
www.alleghenytechnologies.com/ludlum/pages/products/al294c.pdf
apparently it can be welded, although I don't know if it would present any issues for local fabricators
I can't see low carbon being a problem for welding, high carbon yes, but not low carbon. High carbon leads to low ductility in the material, which is a problem. How hot is this? Low carbon does lead to a reduced strength at higher temperatures, say > 900 °F.
The biggest problem with this material seems to be the availability, it is available only in large quantities from the mill and typically sold to manufacturers. I may be able to buy .036 coil from Ryerson Tull, but it appears so far to be rather impractical to have a rectangular liner fabricated for one job. In use temperature is below 300 degrees F, the material is needed to withstand the highly corrosive effects of condensation in the stack. I think the rep was incorrect in his assessment of why the material is only available in round duct, it's probably due to cost, more universal application and the thin gauge they're working with.
Before going any further, I understand you're talking about the chimney (or stack, as Americans call it) that will exhaust the boiler's smoke (or combustion gases) to the atmosphere (or SO2 scrubber). The breeching would be the duct through which the gases leave the boiler and are conveyed to the chimney. Right?
If so, I'll suggest you an entirely different option. Have you thought of lining the chimney and breeching with acid resistant ceramic material i.e., anti-acid bricks or concrete? If it's possible to install them, I would definetely prefer anti-acid bricks or concrete rather than stainless steel.
Giovanni S. Crisi
Sao Paulo - Brazil
You're correct, I'm talking about a chimney and breeching. Unfortunately we have an existing incinerator stack we are trying to utilize and it's only 12X24 inside dimension.
I talked to a metallurgist at the mill and he indicated welding with a filler electrode is problematic. The material can be welded with a seam welder and can be bent 90 degrees but not 270 for example to fold over and press a seam. What is the availability of portable seam welders? Is this equipment that any fabrication shop outside of a factory would typically have?
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