Carbon steel flange is mainly at the end of the flange body made of carbon steel metal material flanged fittings and flanges, the main production process of casting, medium plate rolling, forging, cutting the plate of various methods, such as the quality of the process made of carbon steel flanges flanges is not the same. Carbon steel flanges in China mostly according to the requirements of national standard dimensions, tolerances, such as the production of flange, if it is bad most of the carbon steel flange often obsolete technology or steel itself has cracks appear porosity will be leaking after welding up, such as in the industry for not according to the standard size production of carbon steel flanges flanges have called two standard flange, carbon steel flange pressure mark into the PN mark and Class tag, for PN tag has "PN2.5 PN6; PN10; PN16; PN25; PN40; PN63; PN100; PN160; PN250; PN320; PN400" 12 classes, the Class tag has six classes, mainly "Class150 Class300; Class600; Class900; Class1500; Class2500".

The size of the carbon steel flange according to the national standards, tolerance range, such as the production of flange, the difference in production is not according to the standard size of flange is also called second standard flange (someone called non-standard flange is not correct), usually some unscrupulous merchants will reduce two flange thickness, diameter size to achieve the purpose of saving material, and made from scrap steel and scrap steel flange, is usually the steel chemical composition and mechanical properties of substandard waste, moreover steelmaking production flange with black steel private, the private steel steelmaking technology using old, there is no guarantee that the mechanical properties and welding performance, use which may not be able to and steel pipe welding, such as cracks, porosity or steel itself will leak after welding.