What precautions should be taken when welding stainless steel pipe fittings, stainless steel elbows, stainless steel tees, stainless steel reducers and other pipe fittings?
- To prevent intergranular corrosion due to heating, the welding current should not be too high-about 20% less than that used for carbon steel electrodes. The arc should not be too long, and the interlayer should be cooled quickly, with narrow welds being the best choice.
- Stainless steel pipe fittings become more brittle after welding and are prone to cracking. If typical stainless steel pipe fittings are used for welding, preheating above 300°C and slow cooling to about 700°C after welding must be performed. If the weldment cannot be heat treated after welding, alternative stainless steel pipe fittings should be used.
- To improve corrosion resistance and weldability, appropriate amounts of stabilizing elements such as Ti, Nb, and Mo are added to stainless steel pipe fittings. This results in better weldability compared to standard stainless steel pipe fittings. When using typical chromium stainless steel electrodes, preheating above 200°C and tempering at about 800°C after welding should be performed. If the weldment cannot be heat treated, chromium-nickel stainless steel electrodes should be used.
- Stainless steel pipe fittings have excellent corrosion resistance and oxidation resistance and are widely used in the manufacturing of chemical, fertilizer, petroleum, and medical machinery.
- Stainless steel pipe fittings come with either titanium-calcium type or low-hydrogen type coatings. The titanium-calcium type can be used for both AC and DC welding, but the penetration depth is shallow during AC welding, and the electrode may overheat. Therefore, DC power supply is preferred whenever possible.
- Stainless steel pipe fittings possess certain corrosion resistance (against oxidizing acids, organic acids, and cavitation), as well as heat resistance and wear resistance. They are generally used in power stations, chemical plants, petroleum, and other equipment. However, stainless steel pipe fittings have poor weldability, so careful attention should be paid to the welding process and the selection of appropriate welding rods before heat treatment.
- The welding rod should be kept dry during operation. Titanium-calcium type rods should be dried at 150°C for 1 hour, while low-hydrogen type rods should be dried at 200-250°C for 1 hour. (They should not be dried repeatedly, as this can cause the coating to crack and peel off easily.) Be cautious of oil and other contaminants sticking to the welding rod coating, as this can increase the carbon content of the weld and affect the quality of the weldment.
- When welding stainless steel pipe fittings, repeated heating can cause carbides to precipitate, reducing the corrosion resistance and mechanical properti
