Inconel 625 N06625 - Elevated temperature use

[CuMo]

Has anyone had experience designing at the upper temperature limits of ASME VIII-1 ?
I have an inquiry for a few BEL type tubular heat exchangers where the tubeside has to be designed for 900 deg C (~1650 deg F) flue gas.
Potentially this temperature can be lowered if we opted for the use of ceramic linings & ceramic tube ferrules over carbon steel but I've been asked to ignore this option at this stage and investigate use Inconel 625 only...
The pressure in the tubeside is pretty low ~1 BAR G (~15 psig) so things aren't looking so bad if I am using the allowable design stresses for SB-443 N06625 plate at 1600 deg F (ASME II D).

I'm struggling however on how to approach any forging / bolting materials and where to obtain design stresses from.
Their design stresses don't "go" as high in ASME II D.
Has anyone had a similar scenario before?
Any ideas - welcome.
Thanks!

P.S.-1 I've had a brief discussion with our NoBo and they mentioned that a design life has to be specified due to the time dependent properties of the materials at such high temperatures.
P.S.-2 The exchangers can be designed to any code (not 100% necessary to use ASME VIII-1) but I think the problem would be present with any code.

 

[XL83NL]

I don’t see where 06625 can be used up to 900 deg C in IID (currently looking at the 2019 edt, metric version).
871 is the max for grade 2. In a recent job I had quite some issues finding grade 2, in fact all I could find was grade 1 (I’m in the EU if that makes a difference).
I think VIII-1 is your current best option though. Don’t try EN 13445, using that code for anything above 600 deg C in the creep range is tricky.

Is 06625 a material requirement for corrosion point of view, or other metallurgical reason? If not I suggest to look at 06617; it is readily available and if you need to go ultra high, it is one of the best options, provided it is suitable for the service conditions. Fairly affordable as well, relatively seen.

 

[marty007]

We've also been looking at a very high temperature 625 vessel recently.

We have so far been unable to find the piping we need in the Gr.2 sol.annealed material which is acceptable up to 871°C, everyone only has the Gr.1 annealed version which is only acceptable to 649°C.

Good luck.

 

[CuMo]

XL83NL, you're right. 871 deg C is the maximum for plate.
Our thermal guy has said the temperature can be lowered to fit at the upper end without having an impact. I think he had some safety margin on it (just in case).
Also I had some input from our welding engineer - the limit for the welding consumable is 1000 deg C.

I'm not sure yet about chemical resistance - as far as I know our Client's plant is mostly Inconel so it probably makes sense.
We can look into 06617 - thank you!

Thank you both for the input! Very useful.

Will keep you posted - might be a while though.

 

[XL83NL]

Will keep you posted - might be a while though.

Please do, it's an interesting topic.

06617 is an Inconel as well, although Inconel is just a trade name. Its a nickel alloy, with less nickel and more balanced towards Cobalt (for high temp. application). Whats your stream made of, in terms of composition? At such temperatures I dont see why 617 wouldn't work.