Introduction: 

 Plate flat welding flange (chemical standard HG20592, national standard GB/T9119, mechanical JB/T81): convenient to obtain materials, simple manufacturing, low cost and extensive use; but poor rigidity, so it shall not be used in chemical process pipe matching systems with supply and demand, flammable, explosive and high vacuum requirements, and high and extremely harmful situations. The sealing surface type has both flat and protruding surfaces. 

 Flat welding flange standard: 

 National standardflange refers to flanges produced in accordance with the provisions of the national standard GB/T 9112~9124-2010 Steel Pipe Flange of the People's Republic of China. 

 The national standard flange standard is jointly issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China and the National Standardization Administration Commission of China on January 10, 2011 and implemented from October 1, 2011. 

 GB/T 9112~9124-2010 includes the following 13 standards: 

 Replaced the national standard GB/T9112-2000; GB/T10745-1989 standard 

 GB/T 9112-2010 Steel Pipe Flange Types and Parameters 

 GB/T 9113-2010 Integrated Steel Pipe Flange 

 GB/T 9114-2010 Neck Threaded Steel Pipe Flange 

 GB/T 9115-2010 Butt welding steel pipe flange 

 GB/T 9116-2010 Neck Flat Welded Steel Pipe Flange 

 GB/T 9117-2010 Welded Steel Pipe Flange with Neck 

 GB/T 9118-2010 Butt welding ring with neck loose sleeve steel pipe flange 

 GB/T 9119-2010 Plate Flat Welded Steel Pipe Flange 

 GB/T 9120-2010 Butt welding ring plate loose sleeve steel pipe flange 

 GB/T 9121-2010 Flat Welded Ring Plate Loose Sleeve Steel Pipe Flange 

 GB/T 9122-2010 Flanged Ring Plate Loose Sleeve Steel Pipe Flange 

 GB/T 9123-2010 Steel pipe flange cover 

 GB/T 9124-2010 Steel Pipe Flange 

 Technical conditions: 

 The pressure marking stipulated in this standard is divided into PN marking and Class marking. 

 The PN mark has 12 pressure levels. 

 They are: PN2.5; PN6; PN10; PN16; PN25; PN40; PN63; PN100; PN160; PN250; PN320; PN400 

 Class marks have 6 pressure levels. 

 Class 150; Class 300; Class 600; Class 900; Class 1500; Class 2500 

 Another meaning of the national standard flange is: flanges produced according to the size and tolerance range required by national standards. Unlike flanges that are not produced according to the standard sizes, they are also called two-standard flanges (some people call non-standard flanges incorrect). Usually, some unscrupulous merchants will reduce the thickness and outer diameter of the flange to save materials. There are also use waste steel or corner steel to process flanges. Usually, this kind of steel is waste that does not meet the standard chemical composition and mechanical properties. What's more, the steelmaking technology used in black steel mill is old and cannot guarantee mechanical performance and welding performance. When used, it may not be possible to weld with the steel pipe when used, or the steel itself has cracks, pores, etc. Therefore, try to choose the national standard flange when buying a flange. If you have limited funds to choose a two-standard flange, you must carefully observe and measure the size of the flange to avoid being deceived.