I am trying to determine in which standard the p/T ratings of PN designated valves is given. Or in other words, when a valve is stated to be PN16 Rated - to which standard is is rated as such?

I am aware of BS EN standards that cover the face to face dimensions etc. but I cannot seem to find anything that allows you to look up the material, class, temperature and the corresponding pressure rating for any given PN designation. (Like one does with the tables in ASME B16.5)

I am aware that EN1092-1 covers the p/T ratings of the flanges. Do these extend automatically to the valve as the valve body and components are assumed to be always stronger than the flanges?

Or is there some other theory behind the determination of a PN designated valves p/T rating?

You don't say where you are from, but from the nomenclature, it appears you are talking about European (CE)specs?  The CE Pressure Equipment Directive is 97/23/EN (google on those terms, you should be able to find a copy of this from the CE servers, in the language of your choice).  The PED has tables that specify the pressure and temperature limits for a part to fall within a particular classification.  Moreover, the manufacturer is supposed to maintain the certification, which should include the details of the calculations done to show certification, as well as the temperature and pressure limits defined for the part, in order to comply with the PED.

In general that Paragraph of the standard covers exactly my problem by stating what the recognised codes are for valve design and what p/T ratings are applicable depending on whether you choose to specify the valve using the Class system or the PN system.

This confirms my initial assumption that the pressure rating of the flanges is assumed under EN methods as the weakest point of the valve - albeit I only have confirmation on this for Gate, Plug, Ball and Check valves as these are the valves covered by the above standard.

From a quick survey it would seem that butterfly valve standards along the same lines are still being developed.
"08/30187521 DC
BS EN 593. Industrial valves. Metallic butterfly valves"

BS EN 13397 may cover the same information for metallic Diaphragm Valves - but unless I fork out the cash to buy it I am not going to be sure. Anyone know for a fact?
 
As all EN standards are supposed to be harmonized with the PED - I am confident that the correct way to do things would be to use the method stated in BS EN 13942 to specify my valve pressure ratings/classes as per ASME B16.5 or EN1092-1.

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