In general, the diameter can be divided into seamless steel pipe outside diameter (De), the inner diameter (D), nominal diameter (DN).

DN is Nominal diameter, refers to the nominal diameter seamless steel pipe, is the average of outer and inner diameter.

It is neither nor is the inner diameter of the outer diameter. Water, gas transport pipe (galvanized seamless steel or galvanized steel), cast iron pipe, plastic composite pipe and polyvinyl chloride (PVC) pipe and other seamless steel pipe, nominal diameter should be marked “DN” (such as DN15, DN50 ).

De to external diameter, mainly refers to the seamless steel pipe diameter, PPR, PE pipe, polypropylene pipe diameter, the general De labeling are marked as required in the form of an outer diameter * thickness.

D general seamless steel pipe inside diameter.

d inner diameter concrete pipe. Reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic tubes, cylinder tile seamless steel tubes, diameter to the inner diameter d should be expressed (eg d230, d380, etc.)

Φ representing an average diameter of the circle; may also represent an outer diameter seamless steel pipe, but this should be multiplied by the thickness thereafter. Seamless steel pipe seamless steel or non-ferrous metals, should be marked “OD × wall thickness.”