cryogenic bending/bowing of LNG rundown lines

[jim0210]

Any body in the group had experience in considering cryogenic bending/bowing in their stress analysis of LNG rundown lines. This is the phenomena in which during the period when horizontal pipe lines are partially filled with LNG, a temperature differential from top to bottom of the pipe would occur. This then leads to extra stresses on the elbows of pipes. I would appreciate if you could share to me the method how did you calculate the stresses involving cryogenic bending/bowing. How can you determine for the differential temperature from top to bottom of pipe.

Thank you in advance.

jim0210

 

[pennpiper]

jim0210,
Please explain for us how you have a "horizontal pipe lines are partially filled" By partially filled you mean part liquid (LNG) and part vapor (NG). How is this possible?
PennPiper

 

[jim0210]

An example of Partial filling situation may be an initial LNG filling in to the pipe line (e.g. start up) or an LNG draining out from the pipe line.

Thanks,

jim0210

 

[pennpoint]

Most facilities allow for expansion and contraction of Vacuum Jacketed Piping, utilizing bellows and pressure relief valves at key points in the system. Seek qualified solutions from liquid nitrogen Vacuum Jacketed Piping manufactures.



Best regards
pennpoint

 

[mylexicon]

If I understood your question correctly, assuming the pipe is half filled, you're dealing with differential stresses between the top half and bottom half of your horizontal runs along the pipe due to the temperature gradient from top to bottom of the pipe cross section.
Besides selecting the right material for your pipe, if you're trying to come up with analytical solutions to the stresses developed across the section, the only way to go is by Finite Element Analysis method or a FEA software. "FEPIPE" is one that is costumized for pipe stress analysis. A software like "CAESAR II" won't help you here, because it considers the pipe as beam elements and performs the stress calcs based on beam equations. Or you can go with an all purpose FEA software like "ANSYS". I guess it depends which one is easier for you to get a hold of.
good luck

drno

 

[JohnBreen]

Gentlemen,

L.C. Peng wrote this papaer and it may be useful to this discussion:

http://www.pipestress.com/papers/Therm-Insul.pdf

Regards, John.

 

[jim0210]

Thank you gentlemen for your valuable replies. And also Thank you John for this valuable article by LC Peng it is very usefull.

Thanks again

jim0210