304 SS Performance for 1400F Long Term Application 2

[cadtocam]

Please can any one give me some help?

I am designing a fume thermal oxidizer system. The oxidizer operating temperature is 1400F and will run 22 hours/day, 300 days/year. This system supposes to work 10 years. The discharge of this oxidizer direct connects to a shell and tube Heat eXchanger (HX). Hot and cold airflows in this HX are perpendicular, cold air is 250F.

My boss wants to use 304SS to build this HX and almost every book states that 304SS good for 1500F application. Does any body have experience to share or can provide suggestion? Thanks.

 

[metengr]

For your specific application, I would recommend using AISI Type 304H in lieu of AISI Type 304SS. We have used the 304H grade for exposure to high temperature flue gas and radiant heat (OFA duct work and structural attachments)in our Power boilers with no problems. The reported scaling temperature for 304H is 850 deg C (1562 deg F). The H grade contains higher carbon and is coarse grained for increased creep strength.

 

[metengr]

As a follow-up, make sure you have some understanding of the (fume) gas constituents prior to making a final selection of material. At elevated temperature, the 304H can be subjected to hot corrosion attack from molten salts or exposure to chloride/fluoride atmospheres.

 

[EdStainless]

I presume that this part will not be under any mechanical load. It should work fine as a duct as long as there is external support. 304H will help prevent sag and distortion.
I echo metengr's hot corrosion concern. Any halogens, sulfur, salts or acids should cause you to do a little more research (High Temperature Corrosion of Engineering Alloys, G. Lai, ASM, ISBN 0-87170-411-0).
What will happen when this isn't in use? It needs to be kept hot (over 100F. Other wise you might get condensation, and spalling, and thermal fatigue, and a lot of other problems.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[cadtocam]

metengr & EdStainless thank you for your valuable information. For this application no halogens, sulfur, salts or acids attack, but no guarantee that this HX will be kept hot when oxidizer is not in use, this may cause big problem. Further more, to reduce material cost my boss wants to use 304L, what's the price difference between 304L and 304H? Thanks.

 

[metengr]

I would not recommend 304L. I would stick with 304H for this application. You want the added creep strength and that only comes about with the higher carbon. Edstainless might be able to give you some idea regarding pricing differences. Don't let cost drive this decision.

 

[Lars50]

I can add to what is said previously that there is a material, suitable for high temp application. 153MA or 253 MA supplied by AVESTA. It may be considered as an overkill but does the job for many years, we uses the material at 800 to 900 C for more than 15 years in some applications.