PED fluid state

[europipe]

PED question:
C1 up to C4 is classified under gases.
When I fill in the design temp. of -110 deg C. for eg. ethylene I come up with a vapourpressure of 0 barg,
so this should be a liquid acc. calculation.
The classification 'gas' , is it because I should take the design temp. ambient?

 

[XL83NL]

You need to review all design conditions.

Review article 3, 1.1(a);
gases, liquefied gases, gases dissolved under pressure, vapours and also those liquids whose vapour pressure at the maximum allowable temperature is greater than 0,5 bar above normal atmospheric pressure, (1 013 mbar) ....

Not sure what you mean with C1 to C4 (methane, ethane, propane and butane)? If you review the conditions at the maximum allowable temperature (lets say its the maximum design, which may very well be 21 C - i.e. ambient), and the vapour pressure of your medium under review (i.e. C1-C4) at that temp. is greater than 1513 mbar, you need to consider it as a gas.

So, if your system is solely designed for -110 C as the max design temp. (i.e. it wont get any warmer) and only at that temperature it holds pressure, I can see you could consider it a liquid. But typically, the service can also see pressure while its not at that temperature (yet). The system will probably start of ambient, and may develop a pressure at that time, therefore being a gas acc. PED.

Hope this helps.

 

[europipe]

Thank You XL,

"C1 to C4 (methane, ethane, propane and butane)"is correct.
-110 deg C. for eg. ethylene I come up with a vapourpressure of 0 barg,
so that is less than 1513 mbar
I can find in the Dutch edition of publication (L181/14) an alinea (2.2.1) what says an ambient temp. should also considered.(a little abstract, but do You think this temp. should be used as design?)
Is there still another reference?

 

[XL83NL]

I cant see how you could have a max design of -110 deg C. That would mean that at ambient theres nor pressurised gas, and the gas would be entered in the system when it's at -110 deg C. Think about it. Is that even real? I can't see a reason why...

Don't look for a reference. Try to think how you would defend your design to say a notified body when he asks why you haven't considered this as a gas.

 

[europipe]

We know it's a gas acc. PED.
Hmmm.. Have to convince Young processpeople that they filled in the linelist wrong.
Why shouldn't there be a reference (PED proscribes the designtemp.).
The line is a liquid transportline at -110..
Thanks for your effort.