304 SS in high temperature serviec 1

[jtseng123]

Dear all,

Without specifying the minimum carbon content or "H" grade , can plain SA-240-304 SS, which has carbon content from very low up to 0.08% maximum, be used for 536 degC design temperature ? My understanding is only above 540C, high carbon content 0.04% and above is recommended.

 

[metengr]

First, what is the application? Second look at ASME Section II, Part D for SA 240 304 plate specifically, 1500 deg F is the maximum permitted service temperature.

 

[Afox88]

I believe jtseng123 is referring to note G12 of Section II-D:
"At temperatures above 1000°F, these stress values apply only when the carbon is 0.04% or higher on heat analysis."

The minimum carbon content of 0.04% is required only if you are operating over 1000F. Below that, you are correct that any plain SA-240 SS304 will do. I am assuming Section VIII-1, check with Code your using.

 

[metengr]

Yes, but there is no plain grade of 304 ss under the SA 240 material specification, which is why I stated specifically. The reason is carbon content below 0.03% would be considered 304L per the SA 240 material specification, and limited to 1000 deg F. When you have dual grade certification 304L/304, the 0.04% or higher carbon comes into play for creep strength and one must review the MTR for specific use.

 

[SnTMan]

SA-240 lists 0.08 max C for 304. About any material available should be good, I'd think...

Might specify C of 0.04 Min on any P.O., just to be covered.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[jtseng123]

metengr, this is a condensate pot in ethylene plant. I am looking at Section II Part A, S2, that H grade shall be used above 540C. I just want to confirm that plain SS which can have less than 0.04% carbon content won't cause problem for 536C service. Vessel order was placed and if we add additional requirement of 0.04% minimum, impact most likely will occur that we don't want to have.

 

[EdStainless]

So your design was based on 304L? If not then you need to backtrack and take care of this.
In general you either get 304L (0.01-0.03% C) or 304H (0.05-0.08% C), there is almost no straight grade material made these days.

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P.E. Metallurgy, Plymouth Tube

 

[jtseng123]

EdStainless,
When we specify SA-240-304 SS on vessel drawing according to Section II designation, what will we get from the MRT ? Will it say 304L or 304H ? Shall we reject it if it says 304L or 304H ?

 

[EdStainless]

It might say 304/304L, meaning that it meets the 304L chem restrictions and that at room temp it meets the 304 minimum mechanical properties. Or it might just say 304, and still be 0.015% C. It will not be 304H.
If it is low C, at elevated temp it will only be as strong as 304L so double check your design. If creep is an issue you need to look again.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

There is an absolute dividing line of 1000 F for flanges- above 1000 F you must use H grade. For other components (shells, heads, pipe), you can use the low carbon grades above 1000 F but must use the low carbon stress values for design. The high carbon stress values are of course higher because the alloy is creep resistant.

A design temperature of 536 C implies an operating temperature a fair bit below 536C. Based on past experience, which is all for equipment of fairly limited size, we've never had a problem as long as the appropriate stress values for the material actually being used are used in design.

If it is a condensate pot, what is condensing at those high temperatures?

If you are actually using the equipment at lower temperatures with potential aqueous corrosion, but have a high design temperature due to an upset condition, you are actually in a bad place to use H grade. Low carbon content will reduce sensitization in the heat affected zone, relative to using straight or high carbon grades. In these situations people often consider stabilized grades like 321 and 347.

 

[jtseng123]

moltenmetal, thanks for your input. This condensate pot normal operating is 315C, and as you said, the high design temp is to cover upset case once every 2-3 years if other equipment fails.
Creep shall not be the concern in my opinion. And we have decided to stay with straight 304 SS without asking high carbon content.

 

[jtseng123]

Another issue in my mind for the same topic is:

Can dual certified 304/304L SS be used for high temperature between 800F -1000F for long term service?

For 304L, Div 1 does not allow above 800F. I believe it is due to low carbon that it won't have sufficient rupture strength.
Since dual 304/304L also has very low carbon, I don't think it can be used above 800F. Is it right ?

 

[metengr]

Look again, 304L pipe or tube product forms can be used up to 1200 deg F based on stress lines in ASME Section II, Part D. Please read all of the Notes, I am not going to summarize here.

 

[jtseng123]

metengr, I feel shameful. I opened a hard copy of old code from my bookshelf and it shows 800F for plate, but new code does goes up to 1200F.

 

[metengr]

jtseng123;
No worries. When you stop learning it is time to get out of this business.

 

[SnTMan]

If not before

The problem with sloppy work is that the supply FAR EXCEEDS the demand