DN (Diameter Nominal) mm and inch are used often as well Is it true that for DN XX pipe, pipe outer diameter (O.D.) is XXmm? D.I. pipe size is different from pipe O.D. in any size.

DN (Diameter Nominal) mm and inch are used often as well Is it true that for DN XX pipe, pipe outer diameter (O.D.) is XXmm? Not always. For instance, pipe O.D. of DN15 1/2" pipe is not 15mm; while for size DN350 14" and above, size equals to pipe O.D. AMSE standard is for seamless steel pipe and seamless pipe fitting

No. Outer diameter would not affect bolts going through two flanges, only PCD would. Difference in outer diameter will only affect how it looks.

To choose the right flange, below information is needed: Pitch Circle Diameter (PCD) Number of Bolt Holes Pipe Size Pitch Circle Diameter (PCD) is the diameter of a circle that goes through all bolt holes. Number of Holes matters. Different flanges can have the same PCD with different number of bolt holes. 

Flanges in different standards cannot be used together in most of the sizes. Yet, for some sizes, different standards share the same PCD and number of bolt holes. In this case, they can be used together. Sometimes, people use smaller bolt for flanges with PCD difference less than 5mm to avoid fixing the pipe.

Pressure Gauge 15 PSI = 100 KPA 1 BAR = 1 KG/CM^2 = 100 KPA = 0.1 MPA 50 PSI / 350 KPA / 3.5 KG/CM^2 / 3.5 BAR 100 PSI / 700 KPA / 7 KG/CM^2 / 7 BAR 150 PSI / 1000 KPA / 10 KG/CM^2 / 10 BAR 200 PSI / 1500 (1600) KPA / 15 KG/CM^2 / 15 BAR 300 PSI / 2000 KPA / 20 KG/CM^2 / 20 BAR

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