Pipe design - metric vs NPT

[dahar]

I'm about to get involved in doing piping design for a German customer. Am I correct in assuming that the DN nominal pipe sizes (e.g. 100 sch 40 is the same as 4" sch 40 NPT) are the same as we use in the US?

If that's true why are the pipe flanges different?

 

[JLSeagull]

The ASME B36.10M nomenclature for piping in traditional English units is nominal pipe size. The format of the description is NPS 4 for four-inch nominal pipe size. As 100 mm is nearly the same as 4-inches, NPS 4 corresponds to DN 100. This is reflected on the same table within ASME B36.10M with NPS on the left side and DN on the right side.
The notes reflect that -
“NPS (Nominal Pipe Size) is a dimensionless designator that has been substituted in the customary units section for the previous term Inch Nominal Size.
” DN (Nominal Diameter) is a dimensionless designator used in the SI (metric) system to describe pipe size.