What should we pay attention to when welding stainless steel pipe fittings?

　　The following items shall be noted when welding stainless steel pipe fittings:

　　1. In order to prevent eye-to-eye corrosion due to heating, the welding current should not be too large, 20% less than that of carbon steel electrode, the arc should not be too long, and the interlayer cooling should be fast, and the narrow weld bead should be preferred.

　　2. After welding, stainless steel pipe fittings have greater hardenability and are easy to crack. If the same typical stainless steel pipe fittings are accepted for welding, preheating above 300 ℃ and slow cooling treatment at 700 ℃ after welding must be carried out. If the weldment cannot be subject to post-weld heat treatment, stainless steel pipe electrode shall be selected.

　　3. For stainless steel pipe fittings, in order to improve corrosion resistance and weldability, appropriate amount of invariable elements such as Ti, Nb and Mo are added. The weldability is better than that of stainless steel pipe fittings. When the same typical chromium stainless steel electrode is accepted, it shall be preheated at above 200 ℃ and tempered at 800 ℃ after welding. If the weldment cannot be heat treated, chrome-nickel stainless steel electrode shall be selected.

　　4. Stainless steel pipe electrode has exquisite corrosion resistance and oxidation resistance, and is widely used in chemical, fertilizer, oil, medical machinery manufacturing.

　　5. The coating of stainless steel pipe fittings includes titanium-calcium type and low-hydrogen type. Titanium-calcium type can be used for AC and DC welding, but the penetration depth is shallow during AC welding, and it is convenient to turn red at the same time, so DC power supply is generally accepted.

　　6. Stainless steel pipe fittings have certain corrosion resistance (oxidizing acid, organic acid, cavitation), heat resistance and wear resistance. Generally used for power stations, chemical industry, petroleum and other equipment. The weldability of stainless steel pipe fittings is poor. Pay attention to the welding process and select the appropriate welding electrode before heat treatment.

　　7. The welding rod should be kept dry during operation. The titanium-calcium type should be dried at 150 ℃ for 1 hour, and the low-hydrogen type should be dried at 200-250 ℃ for 1 hour (it should not be dried repeatedly, otherwise the coating is easy to crack and peel off). Beware of the sticky oil and other dirt on the coating of the welding rod, so as not to increase the carbon content of the weld and affect the quality of the weldment.

　　8. During welding of stainless steel pipe fittings, carbides are precipitated by repeated heating, which reduces corrosion resistance and mechanical function.