Causes of weld blackening of stainless steel pipe

During the use and production of stainless steel pipe, the weld position will be blackened. The weld blackening is one of the common welding defects. Why is the weld of 304 stainless steel pipe black? What causes it? How to deal with this situation?
The main reasons for the blackening of stainless steel pipe welds are: oxidation of the weld surface and high temperature oxidation of surrounding materials. The specific reasons are as follows:
1. The stainless steel pipe is not cleaned before welding, and there are oil and other impurities on the stainless steel pipe, resulting in welding blackening;
2. The argon protection is insufficient, the protective gas is impure, and the gas contains oxygen and water. And argon supply is insufficient;
3. Long-time welding;
4. Excessive current,
5. Improper distance between welding tungsten needle and weldment;
6. Improper selection of tungsten needle;
7. The temperature of molten pool is high, and there is no continuous protection after welding;
8. The welding back of stainless steel pipe is not protected properly (the back is blackened).

Stainless steel pipe
Stainless steel pipe