Hi guys, I have a blow-down line (30") which is designed at -25°C because when psv opens the fluid de-pressurizes, thus freezing.

This is the situation almost for 300m, after we estimate temperature increases to -15°C.

My question is:
Is there a problem related to support shoes or saddles freezing? If they freeze ice can lock themselves to steel frames, so I have to avoid it by using support insulation for cold.

Do you have any experience with this situation?

I have experience this from one of the project on my previous company. Basically, we have a flare system which is a carbon steel material A106-B. Unfortunately the process group identified the low temperature blow down due to Joule Thompson effect in the later part of the project. They even have a -60 deg C result from that study. What I remember, process group with the support from stress group prove to client that A106-B is still acceptable with the use of ASME B31.3 Figure 323.2.2B.

But the shoe we use as normal shoe since cold blow down is only occasional.

The temperature you have is still hotter than -29 deg. C, so I think from material standpoint still ok in case you have CS material for the pipe.

Any comments is greatly appreciated.

The only special shoe we use for that flare line is to put a full encirclement pad (to have an axisymmetric configuration in order to avoid stress concentration) at points where AIV is a problem using the EIG guideline.

Sorry Borzki, what are AIV and EIG?

Its Acoustic Induced Vibration(AIV) and Energy Institute Guidelines (EIG) for the avoidance of vibration induced fatigue failure in process piping.

Sigma is correct. To get you up to speed on this AIV phenomenon you can approach your process engineer to calculate the "Sound Power Level, SPL in decibels". Formula is shown in EIG guideline. If I'm not mistaken if the SPL is below 155 decibels AIV is not a concern. If greater then you have to follow the guideline. Our process engineer develops a spreadsheet on this one. Some clients put this AIV in their specs requirements.

To give you an idea of what is AIV phenomenon, this is basically a "High Frequency Acoustic Excitation". Think of a "pipe" as a "loud speaker". If you have thin walled pipe (D/t is high) and have small bore connections (stress concentrations), then the mode of failure is "high cycle fatigue" and failure occur at a short period of time.

Anyway, just ask your senior stress engineer about this one and work hand in hand with process engineer.

Any additional comments appreciated. Please correct me in case I have made wrong statements.

Cheers!!!