Questions about whether European standard flanges can connect metric and imperial pipes?

A comrade asked me about this question before; I think it’s not possible to connect them directly – metric units should be connected using metric connections, and imperial units should be connected using imperial connections

The inner diameters of the flanges for metric pipes and imperial pipes are different, so they cannot be used interchangeably.

Flanges are only divided into European and American standards; there is no such thing as metric or imperial standards

Flanges are only divided into European and American standards; there is no such thing as metric or imperial standards

Flanges are divided into European standards and American standards. European standard flanges are further divided into Series A and Series B. European standard flanges of Series A can be used to connect pipes with imperial dimensions

At present, there are four types of flange standards in use in our country: **national standards (GB/T9112~9124-2000), chemical industry standards (HG20592~20635-1997), petrochemical industry standards (SH3406-1996), and machinery industry standards (JB/T74~86.2-1994).** Although the four types of flanges mentioned above differ in terms of standard grades and industries to which they are applied, the standards they follow are all ISO 7005-1, DIN flange standards, and ANSI B16.5 (petrochemical standards include ANSI 16.47). Only the mechanical flanges use the former Soviet Union’s ГОСТ flange standards, yet these also belong to the European flange system. Therefore, the interchangeability between these different standards and between standard flanges is quite significant. The GB/T9112~9124-2000 series of standards for **steel pipe flanges are based on the use of the HG20592~20626-1997 standards in the chemical industry, which deal with steel pipe flanges, gaskets, and fasteners. The advantages of those standards have been incorporated into these new standards, whose overall structure has been improved to be consistent with or equivalent to that of the standards used in the chemical industry. Interchangeability of flange dimensions between petrochemical industry standards and national standards for flanges belonging to the American system. Flange dimensions belonging to the European system (Series II) in mechanical industry standards and national standards are interchangeable, but there are three flanges in mechanical industry flange standards that cannot be interchanged with national standards: PN0.25MPa–DN500, PN0.6MPa–DN500, and PN1.0MPa–DN80, due to differences in the number of bolts. It can be seen that the standard levels and dimensions of chemical industry standards are basically consistent with those of national standards, allowing for interchangeability of dimensions. Therefore, it is entirely feasible to manufacture valves according to national standard flanges and to use flanges specific to the chemical industry during installation. The so-called national standards refer to the flanges specified by the Ministry of Machinery, or GB flanges such as HG20592~HG20635. The flanges specified by the Ministry of Chemical Industry are revised with reference to ISO7005, ANSI B16.5, and DIN standards; they are not directly based on those standards, and some of their dimensions differ

HG/GB flanges are divided into European standards and American standards. 1. American standard flanges are used for connecting pipes with imperial measurements. 2. European standard HG flanges are further divided into Series A and Series B; flanges of Series A are used for connecting pipes with imperial measurements. 3. European standard GB flanges are divided into Series I; flanges of Series I are used for connecting pipes with imperial measurements

So-called European standard flanges can be used with both imperial and metric pipes. It does not mean that a specific European standard flange is suitable for both metric and imperial pipes; rather, for the same DN, there are flanges that are suitable for metric pipes and those that are suitable for imperial pipes. Apart from the inner diameter, these two types of flanges have the same dimensions and can be connected directly to each other.