B31.3 - elevated temperature considerations and questions

[XL83NL]

Im designing a B31.3 pipe spec for a 900 deg C / 1650 F system (low pressure).
The current idea is to use alloy 800H as it has better strength opposed to the 'straight' 800 grade.
While designing, I stumble on a few problems.


1) Determining flange rating for UNS N08810 in the 1500F-1650F range; ASME B16.5 app. A (2009 edt) provides some direction for calculating flange ratings, however, when I use ASME II-D stress values of SB-564 UNS N08810 flanges beyond 816 deg C (i.e. range where B16.5 stops), I run into the problem that the first calculated value of say 850 deg C gives me a higher pressure than that of 816 deg C; this is because the one for 816 deg C is limited by the ceiling pressure. I thus need the ceiling pressure for 750 deg C but it's not listed. How could one soundly engineer the ratings for temperatures beyond that´s what listed max in B16.5 (i.e. 816 deg C)? The obvious problem are the non-listed ceiling pressure for T > 1500 F. Can VIII-1 app 2 help? If so, whats a suggested approach?

2) Based on other threads, literature and colleague's experience, Im thinking about using Hastelloy X or Inconel 718 studbolts. Which type of nuts could be good for these studbolts? Can I use 'regular' 8MA nuts? Their rating dont go that high, then again, I dont think the nut will be problem ...

3) The W-factor from B31.3 in table 302.3.5 is limited to 1500 F. What are good considerations and literature to review, in order to do the math & homework for the factors in the range 1500 - 1650 F? Can e.g. the material mfr's like Special Metals provide help? Or Becht's article on weld joint strength reduction factor (

http://dx.doi.org/10.1115/PVP2005-71016)?

Or .... ?

Is there maybe some good piping book on these kind of subjects for high temp piping?

Any help is highly appreciated!

 

[BigInch]

I'm staying on my side of the fence.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[XL83NL]

moltenmetal, we're exactly on the same page. You hit the nail exactly where Im after, that is hoping to find someone who has done this before, who can provide me with some useful tips, tricks, do's and dont's, etc... I was aware that flanges should be minimized/avoided; there's still the possibility the piece of pipe itself may not even get flanges.
However, I'd like to assume they are required, do my homework so I know how to design them within Code requirements (if possible within the Code), and hopefully later realize I dont need any, such that I can leave them out. That approach (though more time-consuming) works better for me then hoping they're not needed, finding out last minute I do need a few, and then just erroneously throwing some undesigned flanges in, not knowing when the pipe will pop or the flange will spray, so to say.

I do agree with you that at some point, all of this has to be worked out together with a client. A discussion, where they can provide useful insight based on their experience, is almost mandatory I'd say. Hazards of course needs to be considered properly, and they're linked with the mechanical design. The mechanical design has to provide some means that can minimize or cancel any potential hazard or risk.

However, prior to the discussion with the client, is where this thread is for me; finding out and getting familiar with all desing aspects, defining my 'homework questions', answer those questions myself, etc. By getting helpful replies, I hoped someone could push me towards 'the right library', i.e. a place where I can dig around for a few hours and go through all useful and important details and literature, such that I can have a useful and meaningful discussion with the client. Even though certain desing rules may not be written down with penn on paper, but are gathered through experience, this discussion can still help me.
Having a discussion with a client and not having the right background, or detailed knowledge of certain aspects is useless. Not only do I need to know all thats's required for these kind of applications given a proper mechanical design with as little as possible risk, I also hope to provide the client with relevant aspects of Code requirements, where applicable.
Maybe my very first post had to make this more aware ...