National standard flanges, seeking advice from experts!
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I am currently engaged in the sales of control valves. When collecting data at factory installations, I often encounter a problem, and I would like to seek advice from experts. Among the valves replaced in the factory, most are domestic valves that are quite old; the original documentation for them is no longer available. Therefore, it is possible to rely only on the process data and valve specifications provided by the workers. But problems arise when it comes to the flanges; (most factories want the valves to be delivered ready for installation, just like the original valve flanges, without any need to modify the pipes). However, whether it’s Wu Zhong, Chuan Yi, or Factory 7, they only indicate PN16 and DN50 on the valve nameplates, without specifying whether it’s HG20596 or JB/T followed by some numbers. There are many national standards for flanges as well, and just HG and JB alone already confuse me. I would like to ask experts: what is the corresponding national standard connection specification for PN16/DN50 indicated on nameplates? Is there a big difference between HG and JB? Can the flanges be used interchangeably? Can HG and JB flanges of the same size be distinguished by their appearance? Thank you very much for your reply! !
HG comes in two series; there is information on this in the forums, so take a close look. FLanges of HG and JB with the same size are generally difficult to distinguish from each other in terms of appearance
It’s not easy to tell just by looking at the appearance; it’s best to go to the site and actually measure parameters such as the bolt hole diameter, hole spacing, and hole radius. By comparing these measurements with the relevant standards, it becomes possible to determine which standard the valve conforms to.
JB/T flanges are divided into Series 1 and Series 2. According to JB/T standards, the connection dimensions of Series 1 flanges are interchangeable with those specified in national standards as well as German flange standards, while the dimensions of Series 2 flanges are interchangeable with those of the original manufacturer’s standard flanges.
Flanges according to GB and HG standards come in many different types. There are also the European and American systems. However, flanges of the same type under two different standards generally have similar dimensions, and most of them can be used interchangeably
Problems caused by inconsistent standards and lack of interoperability; support for standardization and interoperability
The pressure for PN16 should be of the HG or JB series. Currently, the SH series does not have PN16. The pressure rating of American standard flanges is the same as that of SH ； The HG series is divided into European and American styles ； The pressure for PN16 is in the European system.
It is highly recommended to abolish departmental standards and adopt **standardized ones! Otherwise, it is not conducive to design, manufacturing, use, and maintenance – it brings only harm with no benefits, and it also gives rise to many problems such as industry protection and local protectionism.
There are truly too many standards for flanges. Among GB, HB, and JB, the bolt hole positions are more or less the same, but the thicknesses and outer diameters vary, which indeed causes a lot of trouble!