Flat welding flange refers to a flange that is connected to a container or pipeline by a fillet weld. It is an arbitrary flange. During design, it is checked as an integral or loose flange according to the degree of integrity of the connection between the flange ring and the straight section. The flange ring has two types: with neck and without neck. Compared with the necked butt welding flange, the flat welding flange has a simple structure and saves materials, but its rigidity and sealing are not as good as the necked butt welding flange. Flat welding flanges are widely used in the connection of medium and low pressure containers and pipelines.

The standards for slip-on flanges mainly include chemical standard HG20592, national standard GB/T9119, and mechanical JB/T81. These standards cover all aspects of the design, manufacture, and use of slip-on flanges, ensuring the quality and safety of the products. Specifically: 

Chemical standard HG20592 provides specific specifications for the manufacture and use of slip-on flanges, ensuring the applicability and safety of flanges in chemical process piping systems. 

National standard GB/T9119 makes detailed provisions on the size, material, and performance of slip-on flanges to ensure their wide application needs. 

Mechanical JB/T81 provides guidance and specifications for the design and manufacture of slip-on flanges from the perspective of mechanical design.

The dimensions of the slip-on flange mainly include the inner diameter, outer diameter, screw hole diameter and the number of screw holes. Specifically:

Inner diameter (ID): The inner diameter of the slip-on flange varies according to the pipe size of the specific application. Common inner diameter sizes are 1/2 inch, 3/4 inch, 1 inch, etc.

Outer diameter (OD): The outer diameter of the slip-on flange is usually larger than the inner diameter. Common outer diameter sizes are 1 inch, 1.5 inches, 2 inches, etc.

Screw hole diameter: The screw hole diameter of the slip-on flange is usually determined according to the required connection strength and thread size. Common screw hole diameters are 1/4 inch, 3/8 inch, 1/2 inch, etc.

Number of screw holes: The number of screw holes on the slip-on flange usually depends on the size of the flange and the required connection strength. Common numbers of screw holes are 4, 6, 8, etc.

Carbon Steel：ASTM A105,20#、Q235、16Mn、ASTM A350 LF1,LF2 CL1/CL2,LF3 CL1/CL2、ASTM A694 F42,F46,F48,F50,F52,F56,F60,F65,F70；

Stailess Steel：ASTM A182 F304、304L、 F316、316L、1Cr18Ni9Ti、0Cr18Ni9Ti、321、18-8；

Alloy Steel：ASTM A182 F1、 F5a、 F9、 F11、 F12、 F22、 F91、A182F12、A182F11、16MnR、Cr5Mo、12Cr1MoV、15CrMo、12Cr2Mo1、A335P22、St45.8/Ⅲ；

Flat welding flanges are widely used in chemical, construction, water supply, drainage, petroleum, light and heavy industries, refrigeration, sanitation, plumbing, fire protection, electricity, aerospace, shipbuilding and other basic projects.

The main advantage of the flat welding flange design is that its cost is relatively low and it is suitable for situations where the medium conditions are relatively mild, such as low-pressure non-purified compressed air and low-pressure circulating water. This flange connection method is to insert the pipe fitting into the flange and adjust it to the appropriate position before welding. Its sealing effect depends entirely on the application of flange gaskets and is fixed with bolts. In order to prevent the flange from deforming under the action of bolts, the inner wall of the flange is generally thickened during manufacturing, which makes the weight of the entire equipment relatively large. In order to improve this, the flat welding flange design abandons the use of traditional gaskets and adopts the design of sealing rings, which not only improves the sealing performance, but also reduces the weight of the entire device, making it more convenient to use.