The standard dimensions used for pipe are fairly global. The pipe dimesions are nominal and rounded. For example, NPS 20 (nominal pipe size 20 inch) has the same outside diameter as DN 500 (diameter nominal 500 mm). These simply identify the pipe, but do not necessarily correspond to precise dimensions. In the case of NPS 20, the outside diameter is 508 mm. Regarding DIN, which are German standards, I believe that most if not all of the ASME B36.10 (it is now ASME) diameters are included in the DIN standards.