Markings on the flange

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The current flange standards in China include **general standards, chemical industry standards, mechanical standards, petrochemical standards, etc.** There are so many of these standards that it can be confusing, and each standard sets requirements regarding the markings on flanges. Here, we will take the chemical industry standards (PN series) as an example to explain the markings on flanges. I. The standard number “HG20592-2009” is the standard applicable to this flange. Here, HG/T 20592-2009 corresponds to the “PN series” of standards in the chemical industry, while the “Class series” standards are represented by HG/T 20615-2009. Due to the large number of flange standards, to make identification easier, remember that those starting with HG are chemical industry standards, those starting with GB are national standards, those starting with JB are mechanical industry standards, those starting with SH are petrochemical industry standards, and those starting with CB are marine standards. As for foreign standards, those starting with ANSI are American standards, those starting with DIN are German standards, those starting with EN are European standards, and those starting with JIS are Japanese standards. Are there any other commonly used standards? Feel free to add more. II. Nominal size: The “DN25” in the figure represents the nominal size of the flange, which may be followed by the outer diameter series of the applicable steel pipe. According to current chemical industry standards, for integral flanges, flange covers, lined flange covers, and threaded flanges, the marking indicating the applicable series of outer diameters of steel pipes may be omitted. For flanges applicable to steel pipes in Series A of this standard, the marking indicating the outer diameter series of the steel pipe may be omitted ； Flanges for steel pipes of Series B conforming to this standard are marked as “DNXXX(B)”. Additional note: The outer diameters of steel pipes covered by chemical industry standards include Series A and Series B. Series A is the internationally standard series (commonly known as imperial pipes), while Series B is the series used in China (commonly known as metric pipes).