For the heat exchangers of DN325 and DN400, do the numbers 325 and 400 refer to the inner diameter or the outer diameter?
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For the heat exchangers of DN325 and DN400, do the numbers 325 and 400 refer to the inner diameter or the outer diameter?
For cylinders rolled according to standards, the nominal diameter refers to the inner diameter; for steel tube cylinders, it refers to the outer diameter. Generally, those with smaller diameters are made of steel tubes. According to JB-T 4715-92, which specifies the types and basic parameters of fixed-plate heat exchangers, 325 indicates cylinders made of tubes, while 400 indicates those rolled. This post was last edited by LTY on 2009-3-21 10:09]
We generally follow this convention: for seamless steel pipes, we use sizes such as φ325, φ426, etc., while for welded pipes, we use DN designations, such as DN300, DN400, etc
DN400 inner diameter; DN325 outer diameter.
DN325 is the outer diameter, while DN400 is the inner diameter.
The identifier is wrong! There is no DN325 specification; it should be φ325. DN400: It is coiled, referring to the inner diameter; the outer diameter is φ(400+2δ). If it is a seamless tube, it should be φ426.
DN400 pipes are generally difficult to roll into cylindrical form, and due to limitations in sheet size, it is hard to grind the inner surface of the welds after the cylinders are joined. It is possible to purchase pre-formed DN400 pipes, which are available in specific lengths; φ325 represents the outer diameter of such pipes.
DNxx is definitely the nominal diameter; if it’s larger than that, it’s the outer diameter, and if it’s smaller, it’s the inner diameter
Generally, DN400 refers to the inner diameter when it is in coiled form; 325 usually refers to tubes, and that is the outer diameter!
I think it refers to the nominal diameter; it indicates a specific specification for the pipe. This denotes the pipes in this series. The inner and outer diameters of DN400 pipes depend on the specific size of the pipe chosen, and the wall thickness varies as well.
Nominal diameter
For heat exchangers with steel tubes as the shell, the outer diameter is referred to; when the shell is made by rolling, the inner diameter is what is considered
DN325 refers to the outer diameter of the cylinder; in this case, a steel pipe with an outer diameter of 325 should be used. The cylinder for DN400 can be either a rolled cylinder or a steel pipe; when it is a rolled cylinder, the inner diameter is 400, while when it is a steel pipe, the outer diameter is 426.