Diameter (Ø) & Norminal size (DN) & Inch
1. Details about "Inch"
Inch is commonly used units of specification in the American system, applying to steel pipes, valves, flanges, elbows, pumps, tees and beyond. Its called 4 inch same as DN 100. Abbreviated as In, originally means thumb in Dutch, and one inch is the length of one thumb. Of course, peoples thumbs also vary in length. In the 14th century, King Edward II promulgated the " Standard Legal Inch". The stipulation is that we select the 3 largest wheat kernels from the middle of the barely ear and arrange them in a row and the total length will be one inch.
2. Meanings of DN
DN is a extensively used specification unit in both Chinese and European systems. It also identifies the size of pipelines, valves, flanges, pipe fittings and pumps. Its called DN 100 equal to 4 inch. It refers to the nominal size of pipelines. Note that this is neither the outer diameter nor the inner diameter but the average valve of the OD and D, known as the average outer diameter.
3. Awareness of diameter (Ø)
Ø is a general unit, which refers to the outer diameter of pipes, elbows, round steel and other materials. It can also be said to be the diameter. For example, Ø510mm means that the outer diameter is 510 mm.
INCH & DN Comparison Table
It should be noted that when you convert DN to OD under GB standard, there are two types of outere diameter sizes (a few of which have the same OD). I series basically are suitable for American system while II series is an earlier commonly used pipeline OD size in China. For instance, we called it DN100 I steel pipe or DN100 II steel pipes.
Other Instruction
(1) For water, gas transmission steel pipes (galvanized or not), cast iron pipes and plastic pipes etc, they should be marked with norminal size "DN"
(2) For seamless steel pipes, welded pipes, spiral pipes, stainless steel pipes and other materials, the pipe diameter shall be noted as OD x WT.
(3) When the nominal diameter DN is used to represent the pipe diameter in the design, there should be a comparison table between the nominal diameter DN and the corresponding product specifications.
