Can anyone enlightened me the other differences between PN and ASNSI rating apart from their pressure and temperature limitations.Example(PN40 to ANSI 300)
As Biggy said: ANSI is an "imperial" Standard while "PNxx" is "metric" ... if you're trying to match an ANSI flange with a PN flange, you won't.
The common thing to do is asking the vendor (when you face a piece of machinery with "PN" flanges) to supply also the counter-flanges (as and additional ... yes, but this is less expensive that asking them to use an ANSI flange providing PN flanges is their standard)