Why is the nominal diameter of the flange inconsistent with the tube?
Just a nominal diameter size series, but also has the difference in the same series, such as DN200 steel, the diameter is the same, but because there are a variety of wall thickness diameter so also vary, so the pipe is not free exchange. The neck flange as an example, the same is the butt welding neck flange DN200 PN2.0, the general size is the flange body size, such as the diameter of flange, flange thickness, flange bolt hole size, hole spacing and bolt hole number, but the flange neck size is not the same, so we as a DN200 tube with time hubbed welding flange, flange and pipe to ensure the uniform size of neck size. Because the nominal diameter is 200 so the flange neck diameter is fixed as the pipe diameter, the thickness of the flange neck according to the thickness of the steel tube, only the inner diameter, after welding to ensure welding, the film does not leave the shadow. Elbows, three links and so on are the same. Is the same with the DN200 elbow, three links, and the outer diameter of tube, but the elbow and tee three diameter according to the diameter of the tube, no matter what change the diameter, flange, elbow, three square meters called DN200 to various types of pipe fittings, simple, this is the meaning of nominal diameter.
The nominal diameter of the 1. flanges does not mean any flange nominal diameter, but only the specifications of the flange. Refer to flange standard for specific dimensions. For example, DN100 does not mean that the flange diameter is 100, depending on the flange pressure, the specific size of the standard.2. nominal diameter of the pipe does not mean the specific size, the specific size should be based on the pipe number, check the standard.3.DN: dimensional identification of combinations of letters and numbers used in piping system components. It consists of letters DN and followed by dimensionless integer numbers, which are directly related to characteristic sizes such as the aperture or outer diameter (expressed in mm) of an end connector.Note 1: unless otherwise specified in the relevant standards, the figures behind the letter DN do not represent measurements or are used for computational purposes.Note 2: the standards used in the DN marking system shall give the relation between the DN and the size of the pipe element, such as DN/OD or DN/ID.
To put it simply, the inner diameter of the flange is the outer diameter of the tube
