Introduction of precautions when using flat welding flanges

Flat welding flange refers to a flange that is connected with a container or pipeline by fillet welds. It is an arbitrary flange. When designing, according to the integrity of the connection between the flange ring and the straight cylinder section, check the integral or loose flange respectively. Flat welding flange not only saves space and weight, but more importantly ensures that no leakage occurs at the joint and has good sealing performance. The reduced size of the compact flange is due to the reduced diameter of the seal, which will reduce the cross-section of the sealing face. Compared with the butt welding flange with neck, the flat welding flange has a simple structure and saves materials, but the rigidity and sealing performance are not as good as that of the butt welding flange with neck. Flat welding flanges are widely used in the connection of medium and low pressure vessels and pipelines.
Precautions for the use of flat welding flange products:
1. In order to prevent the corrosion between the eyes due to the heating of the flange cover, the welding current should not be too large, less than about 20% of that of the carbon steel electrode, the arc should not be too long, and the layers are cooled quickly, and a narrow weld bead is appropriate.
2. The electrode should be kept dry when using it. The titanium calcium type should be kept dry at 150 °C for 1 hour, and the low-a hydrogen type should be kept dry at 200-250 °C for 1 hour to prevent the coating of the electrode from sticking to oil and other dirt, so as not to cause welds. Increase carbon content and affect weldment quality.
3. When the flat welding flange pipe fittings are welded, carbides are precipitated by repeated heating, which reduces the corrosion resistance and the mechanical properties of the product.
4. The chrome flat welded flange pipe fittings have large hardening American standard flanges after welding, and are prone to cracks. If the same type of chromium stainless steel electrode is used for welding, preheating above 300°C and slow cooling after welding at about 700°C are required. If the weldment cannot be subjected to post-weld heat treatment, the flat welding flange pipe fitting electrode should be used.
5. For flat welding flanges, appropriate amount of stable elements such as Ti, Nb, Mo, etc. are appropriately added to change the corrosion resistance and weldability. The weldability is better than that of chrome flat welding flanges. When using the same type of chrome flat welding flange electrode, it should be preheated above 200°C and tempered at about 800°C after welding. If the weldment cannot be heat treated, the flat welding flange pipe fitting electrode should be used.