In order to select correct types of valves, flange, fittings, we need figure out the pipeline specification. Here we discuss abot the definition of De, DN, D, d, Φ

1.   DN (Nominal Diameter) means the nominal diameter of the pipe, which is the average of the outer diameter and the inner diameter. The value of DN = the value of De - 0.5 * wall thickness. Note: This is neither the outer diameter nor the inner diameter.

Pipes such as water and gas transmission steel pipes (galvanized steel pipes or non-galvanized steel pipes), cast iron pipes, steel-plastic composite pipes and polyvinyl chloride (PVC) pipes shall be marked with the nominal diameter "DN" (such as DN15, DN50).

2.   De (External Diameter) means the outer diameter of the pipe, PPR, PE pipe, polypropylene pipe outer diameter, generally marked with De, all need to be marked as the outer diameter * wall thickness form, for example De25 × 3.

3.   D generally refers to the inner diameter of the pipe.

4.   d generally refers to the inner diameter of the concrete pipe. For reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, cylinder pipes, etc., the pipe diameter should be expressed by the inner diameter d (such as d230, d380, etc.).

5.   Φ indicates the diameter of the ordinary circle; it can also indicate the outer diameter of the pipe, but at this time it should be multiplied by the wall thickness. For example: Φ25×3, which means a pipe with an outer diameter of 25 mm and a wall thickness of 3 mm. For seamless steel or non-ferrous metal pipes, “outer diameter × wall thickness” shall be marked. For example, Φ108×4, Φ can be omitted. China, ISO and Japan's partial steel pipe standards use wall thickness dimensions to indicate the wall thickness of steel pipes. The specification for the specifications of such steel pipes is the pipe outer diameter x wall thickness. For example, Φ60.5×3.8.

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