Temperature rating of forged flanges

[ChemEHiker]

I am designing a part, in accordance with ASME B31.1, for 900 psig & 900°F, in 316 stainless. I wish to use a 3/4" forged flange (A 182). Table 2-2.3 in ASME 16.5, for 316-L grade, only goes up to 850°F, even though Table A-3 in B31.1 appears to allow this material to be used at higher temperatures. Table 2-2.2 would allow me to use 316 straight grade for temperatures in excess of 850°F, however all forged flanges these days are dual rated.
Can I use a dual rated flange and take advantage of the higher temperatures in table 2-2.2? Should I make the flange out of A240 plate and go through the flange calculations?

 

[metengr]

You cannot use dual certified and take advantage of higher allowable stress. Use the higher carbon version to ensure adequate
creep strength.

 

[mrfailure]

Using the high carbon version of 316 may be a real problem if you are planning to weld the flange. You then likely would have issues with sensitization.

Aaron Tanzer

http://www.lehightesting.com

 

[metengr]

I disagree. It is done for high temperature service applications. You need the higher carbon content for creep strength to avoid relaxation. Sensitization will occur regardless because of elevated temperature exposure in service.

 

[mrfailure]

Sensitization occurs in the range of approximately 1250 - 1650 deg. F. 316 is prone to chromium carbide precipitation in this range. This is of concern during welding if the flange is to be welded. In that instance, the low carbon 316L grade would be required. The 900 deg. F operating temperature will not sensitize this material during service though.

Aaron Tanzer

http://www.lehightesting.com

 

[metengr]

Understood. Maybe I should explain my position this way, sensitization is not an issue with continuous operational exposure at 900 deg F. If you are concerned with water-wetted exposure at much lower service temperatures, this would be a concern. 316 stainless steel flanges are supplied for elevated temperature service, of which this application certainly applies.

 

[mrfailure]

I agree with metengr about sensitization causing corrosion concerns at lower temperatures. I have run into these issues with high temperature equipment being exposed to ambient environments during maintenance shutdowns. Don't know if that is an issue here though.

Aaron Tanzer

http://www.lehightesting.com

 

[metengr]

By the way mrfailure having been in the Power Generation sector for a number of years, I have even seen what is called low temperature sensitization (LTS) where residual cold work from manufacturing a flange was around 10% with no post forming solution anneal, and continuous exposure at 950 deg F for many thousands of hours resulted in sensitization.