PN Designated Valves - Pressure Temperature Ratings

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.

Hope that helps.  Though, being from the wrong side of the pond, it probably doesn't.
I am working out of the UK - I am currently writing up valve and piping specifications.

Using
the ASME system in this regard is A LOT simpler in that one can simply
state - Class 150# as per ASME B16.5 Table 2..... etc. when specifying a
valve. Proof of compliance with this is then up to the manufacturer.
Also ensuring that you are specifying something that meets both the
pressure and temperature conditions you require is then taken care of.

Most
of the components that I am specifying fall into Class 0 of the PED
with a limited number falling into Class I. In other words they only
require sound engineering practice in terms of their design - with those
in Class I not requiring a CE marking as far as I understand.

So if I understand you correctly what you are saying is:
Ensuring
p/T compliance using the EN 'method' would then require specification
of a nominal rating of PN16 (for example) and going out, finding
products that comply with this spec. Then requesting p/T curves for the
product/s and ensuring that the product meets the worst case scenario
(WCS) for p/T that you are trying to cater for. Alternatively you could
state what your WCS is then go out on enquiry with that p/T information -
which means that you may end up getting a valve with a nominal pressure
rating of PN40 in order to meet the pressure requirements at elevated
temperature.
Either method requires the PN rating to be updated on
the datasheet based on the limitations of the final chosen product -
unless you get it right first time; with the first requiring
considerably more work in terms of picking the final chosen product.

Now
- before I look like one of the guys on these forums trying to get a
quick and easy solution - I am not trying to get out of doing the work
by any means - my basic problem is trying to figure out the industry
standard way of specifying the pressure rating of valves to EN
specifications so that I can ensure I get the same thing every time with
minimal trawling through the limitless number of valves available out
there.

From the originalgatevalve
.