National standard pipe and fitting outer diameter
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The outer diameter of the pipe fittings in the national standard pipe fitting standard GB/T 12459 is as follows. The Series 1 outer diameter of the DN65 and DN125 pipe fittings is different from the Series 1 outer diameter of the pipe in GB/T 17395. If Series 1 is used, there will be problems in welding. They are both national standard systems. Why does one use ISO 4200 and the other uses American standards for the outer diameter system? Please give me some advice, thank you!
National standards are all translated from foreign countries, and the standards of different industries are translated into different foreign standards. National standards have always been confusing in terms of customization of sizes.
Generally speaking, the key engineering diameter is not directly related to the outer diameter. It is a value that intervenes between the outer diameter and the inner diameter. This nominal value is more used to facilitate unification with other accessories, such as elbows, flanges, etc. Under normal circumstances, no matter how thick the wall thickness of the pipe is, its outer diameter is the same, and no matter how high the pressure is, the inner diameter of the flange is basically the same, so as to facilitate the connection with the pipeline.
GB/T12459-2017 is the latest version. 73 refers to the American system and 76 refers to the European system. The difference between 141.3 and 139.7 is also caused by the issue of standard updates and the numerous domestic standards. In fact, the problem is not that big.
In fact, to put it bluntly, the national standard is the fusion of the European standard and the American standard.