Pressure Class #150 / #300 vs NP20 / NP50

Strange question, are you designing acc. EN (DIN) or ASME ?
In general companies have only one of the two.
NP20 and NP50? where did you get that?
Don't you have pipespecs with temp. and press. ratings over there?

Greetings

Hello Europipe,

Thank for your reply, the story is as follows:

The design is according EN (DIN) and the application is related to an offshore electrical platform (not oil & gas).

The highest pressure in the whole system is not more than a few bars (<5bars) and the temperature is ambient (<40dgrs).

Since the application is offshore, there are a number of "engineering comments" suggesting to use Class 150 (PN20) flanges in general and Class 300 (PN50) for instrument flanges. From the technical point of view PN10 should be enough for the whole system.

Of course I can find flanges and piping for whatever pressure I want, however, I see offshore norms starting with Class 150 as lowest and 300 for instrumentation. I see the same in instrumentation (just level measurement). May be paranoid reading from my side.

I do not want to overdimension things, that is not good practice. I just wonder if there are regulations requiring min pressure design and particular requirements for instrumentation.

Thanks in advance for your advices.

Best Regards/ Choromo

As far as I know there is not a rule, but instrument connections are sometimes with higher rating in the small bore range only, for two reasons: the first is to have a stronger assembly. Expecially if you have a flanged nozzles on tanks the use of 600lb. or 300 lb. can avoid further supports on the assembly, like bracing to withstand the instrument. The second is to reduce the number of connection types, expecially because 300 and 600 have the same connection up to dn40.
Be careful that normally instruments on the same equipment have the same piping class
Greetings
Rob