cryogenic piping stress analysis 1

[SAPIII]

It will be of great help to me if you kindly let me know the basic design criteria of stress analysis of cryogenic piping (LNG) subjected to -160 deg c. Further is there any special code requirements are to be considered.
Thanking you in advance for the help.

 

[JohnBreen]

Hello,

The B31 Code that was going to be the cryogenic piping Code would have been B31.10. However, that committee decided that it was so much a parallel to B31.3 that they recommended that it be folded into the B31.3 Process Piping Code (this same process happened to the would-be B31.6 Chemical Plant piping Code - it was also folded into B31.3). There are some special considerations for cryogenic piping but for the most part they center around material selection.

The B31.3 Code was reviewed and changed where appropriate for cryogenic piping design to include special consierations for material ductility, fabrication and testing. The topic of cryogenic piping design is now adequately addressed by B31.3.

With that as background, it is easy to see that B31.3 has the broadest scope of any B31 Pressure Piping Code. That is why the B31.3 committee created rules for various "fluid service categories" (category "D", "M" and "normal service&quot. The idea is that within B31.3 there should be a degree of rigor (for design, fabrication, erection and testing)that is appropriate for the severity of service and potential risk.

Cryogenic piping is the prime example of systems where the "operating temperature" is lower than the "installed ambient temperature" (at ambient installed temperature, the piping is essentially "stressless" when only displacement (expansion/contraction) stess is considered. So when calculating the displacement stress range, the range of temperatures from the hottest (maybe "out-of-service" on a hot summer day) to the design operating temperature (coldest) is used. A departure from the more frequent case where the operating temperature is the hottest temperature (with the exception of off-design upsets)and ambient ("out-of-service" on a cold winter night) is the coldest temperature.

Bottom line, use B31.3 but pay attention.

Best regards, John

 

[JohnBreen]

Hello,

This is another area where it would be good to read the two contemporary books about B31.3 Process Piping design. For more information on these books see:

http://www.asme.org/newrelease/procpiping.html

This is the new book by Dr. Charles Becht (a B31.3 committee member).

Also see:

http://www.casti.ca/

Look for the excellent book by (B31.3 Code Committee member) Glynn Woods and Roy Baguley. "Guidebook to ASME B31.3 - Process Piping" It has been updated to cover the 1999 Code edition and 2001 Addenda. The 3rd edition of the Guidebook now is available.


Regards, John.

 

[MJCronin]

SAPIII,

What do you mean by "basic design criteria of stress analysis " ? To me, these are two seperate things.

If you mean a flexibility analysis, as required by ASME B31.3, then, yes you should evaluate the flexibility of the piping. in accordance with the rules contained within B31.3

The CAESAR-II and other computer based software programs a can perform this type of analysis.

Cryogenic piping "contracts" between anchor points when at operating temperature. This must be considerered in the piping layout.

Additionally, I would add "The Piping Handbook" by Nayyar to the book list suggested by John Breen...... it has a chapter on cryogenic systems.

Hope that this helps....

MJC