cryogenic piping stress

[106coral]

Hello,

I am trying to conduct strss analysis on ethane liquid piping systems.

Design temperaure of this piping is ranged 150F to -200 F at 375psig and operation condtions was given -169F at 172psig.

This piping was constructed 20 years ago but supports rearragement are required due to settlement on site.

As well, in case above I wonder what ambient installation temperature is to set up in Caesar.

I think in new pipig systems ambient temperature may be used default temperature of 70F.

I would really appeciated some experts'advice.

Regards,

 

[JohnBreen]

Hello 106coral'

Well, I am not an "expert" (nobody is) but I will offer this:

You will need to consider three issues and set up your load cases accordingly.

First you will want to calculate the primary stresses due to sustained weight (dead weight and live weight) and sustained internal design pressure. Of course, the temperature really will only come into play here if expansion/contraction will cause the pipe to "lift-off" one or more of the supports thereby effectively "removing" the support (more discussion of this follows).

Next you will need to address the secondary stresses due to the TOTAL THERMAL RANGE OF EXPANSION/CONTRACTION. The thermal range at issue is from minus 200 degrees F. to plus 150 degrees F. This is a thermal range of 350 degrees F. Assuming you keep the C2 default ambient temperature of plus 70 degrees F. you will want to do one of two things. You can set up the thermal design temperature to be (70 plus 350 equals) 420 degrees F. Alternately, you can set up the thermal design temperature to be (plus 70 minus 350 equals) minus 280 degrees F. For a linear analysis of your piping system either way will return the same calculated thermal stress range (displacement stress range).

For your operating conditions (temperatures and pressure) you will be interested in knowing what your equipment loads will be. You will be interested in performing a cold operating case from plus 70 degrees F to minus 169 degrees F (and 172 psig - although it is unlikely that the pressure difference will affect this calculation) to determine if any supports are affected (be sure all supports remain "in-play"). Also, this analysis will tell you what "cold operating condition" loadings you will have on your vessel nozzles, pumps and any other strain sensitive equipment. Similarly, you will want to perform a hot operating case from plus 70 degrees F to plus 150 degrees F for the same reasons stated above (it would be OK to use the hot young's modulus for this - but you would not use the calculated stresses calculated by this analysis in your report).

You may want to read the C2 manual discussion of “C Node” use to model the ground settlement caused displacements at support points.


Regards, John.