Slip-On Flange to Pipe Welding

DN represents a size as NPS and not means DIN. Also, PN means flange Class or Rating.

Example: Flange with DN 50 & PN 20 (not PN 25) means flange with NPS 2 & Class 150.

Please see the attached file: ASME_Flanges_Class (PN) & NPS (DN).

when you have a flange specification given by DN and PN then its DIN standard where ASME standard is given by NPS and class.

Are you saying they are same!!

NPS, followed by a dimensionless number, is the designation for nominal fitting size. NPS is related to the reference nominal diameter, DN, used in international standards and not DIN. Please don't mix between DIN and DN.

See Para. 3 of ASME B16.11:

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Thanks for the useful table

Can you please tell me how to know if a pipe flange is manufactured as per ASME or DIN standard based on specification. what i know is that ASME and DIN flanges will not have same dimensions and thus will not fit together.

Best regards

Yes, you are wright where the ASME and DIN flanges will not match each others from the dimensions. And a very easy way to recognize the ASME flange is to find that the words of NPS (4), Class (150) and Material in ASME (SA) or ASTM (A) like that figure: