Low Design Temp for Piping 3

[Krausen]

I'm in the process of writing oil & gas facility piping specs for cold weather regions in ND & MN. My question has to do with API/ASME's treatment pipe & fittings with design temperatures below -20 F. I know many of their specs address higher temperatures, but often they seem to be capped to -20 F on the low end. For example, flange connections under ASME B16.5 only have pressure class ratings down to -20 F for their materials.

How does a guy write a piping spec if his minimum design temp is -35 F?

Thank you in advance.

 

[Krausen]

Like I say BigInch, just leaning to go with the low temp CS route as of now. It appears to be the correct move, even though it's rare in the US. There will be no demands on my end though.

standweld - you bring up a good point and it's understood the crude oil will never actually reach -35 F while being pumped through the system. But a unit shutdown event in a -35 F ambient environment (outdoor, above ground piping) for an indeterminate amount of time is a definite possibility, as I understand. So, I'm subjected to the client's conservative design standard here. Whether or not this specific crude oil would solidify inside the pipe at -35 F I can't say for sure.

 

[SNORGY]

Can you take advantage of ASME VIII D-1 UCS-66 or B31.3 323.2.2 to see what MDMT reduction you might be able to rationalize before necessitating A-333-6? It does force some pipe and equipment stress analysis to be done up front, but it's worth a shot.

 

[BigInch]

I don't know of a crude that won't freeze solid at that temp.
You are way below the pour point of diesel (lowest around -18C).
If freeze is a possibility, say due to loss of circulation, there should be some contingency plans, double, or tripple pump configuration, steam, or heat tracing, tank heating, replacing line pack with gasoline, etc., something, if you want to have a chance to restart again before summer comes.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[stanweld]

If a unit shutdown occurred, would the line be pressurized? If so heat trace as Big/Inch recommended; even if not, heat trace. It appears to be a moot point anyway, since your Client has dictated the low temp design.

I had a similar case when the seawater injection piping at Prudhoe Bay was required to be designed at -50F. Because it was impossible for the pipe system to be operated at this temp or even near it, the Client changed its design criteria and saved millions.