treating 304 to get 304H 4

[rapid1348]

Dear Specialists

What is the major difference between 304 and 304H type ss?
Is it possible to treat 304 in a way that it has the same characteristics of 304H of SA-240 family by controlling the carbon content? If yes , how?

Regards

 

[ijzer]

If the carbon content of the 304 is 0.04 or higher and the grain size is 7 or coarser it can be classified as 304H.
The grain size can be influenced by the solution anneal temperaure. You can't change the carbon content.

 

[EdStainless]

If you have some high carbon 304 you could reanneal in order to increase the grain size. This will improve the high temp creap properties.
Even if the carbon isn't high enough you could always increase the grain size to help with creap. The code doesn't give you any consideration for this, but it might help in service.

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Corrosion never sleeps, but it can be managed.

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

 

[unclesyd]

If you are going to use this material in a code application the manufacturer has to make the determination and so state that the material meets the specification for 304H.

The practice of increasing the grain size by over annealing is not recommended as standard practice. If this process is not carefully controlled you could easily end up with a material that unsuitable for anything. The results of most attempts that I've seen have turned out to be very bad and the material ended up with very severe metallurgical notches that are the origin for all types of bad things that can happen to SS.

 

[metengr]

unclesyd is absolutely right on the money concerning the risk of substituting non-H grade austenitic stainless steels to be used as reheater or superheater tubing in Power boilers.

 

[rapid1348]

Thanks alot for yoru advices.Could you please introduce some technical articles or sources in this regard enabling me to get more information on the process and its industrial applications.
Dear Metengr, is there any source for such prohibition in the reheater or superheater tubing ?Frankly speaking , we have got the same problem with our vendor right now because he is going to use treated 304 instead of 304H for the tube sheet of the onvection coils of a Reformer in an ammonia plant.
Your collaboration would be highly appreciated.

Cheers

 

[EdStainless]

IF you have material certified as 304 and the carbon is above 0.04%, and the grain size is 7 or coarser, and it meets the required mechanical properties, you can re-certify it as 304H. If you don't meet all three criteria the answer is no.

I am not sure about the plate market. I know that if I want sheet or strip to manufacture tubing the mills are requiring 100T lot purchases.

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Corrosion never sleeps, but it can be managed.

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

 

[metengr]

rapid1348;

I believe what you are asking is does the code permit the use of 304 SS material for tubing, forgings, etc., the answer is yes. You need to carefully review your service conditions to determine if the 304 SS could be used for your tubesheet application. If it could be used, I would make sure the material is certified as 304 SS or 304H.

My comment above for RH and SH tubing refers to original boiler design conditions. If I were to use 304 SS in our high temperature SH or RH pendants or platens, the Code would permit its use. However, this material would not perform as well as 304H in gas touched service. The materials endorsed by the ASME B&PV code must be selected for use by the designer, who should consider actual service conditions.