supercritical ethylene Temperature effect

[SKF852]

Dear all,

I have this problem related to an underground ethylene pipeline of +10 kms in length.
There are TSO valves on both sides and it is operated at ground temperature at 90 barg.

The supercritical P and T of ethylene is 50.4 barg and 9.2°C.

Do you need protection for thermal expansion in case a large amount of ethylene gets blocked in? I would guess in case of temperatures > 9.2°C its not necessary as it is a compressible fluid.
But what happens if the temperature drops below the critical temperature but is still above the critical pressure? Will it behave like a liquid? How does the phase transition happen?

Best regards,
SKF

 

[georgeverghese]

Have my doubts if it will still be above Pc at <9degC when the line is blocked in. As temp drops, gas will condense and internal pressure will collapse and bring this mix into the 2phase region.