The pores of CO2 gas shielded arc welding are mainly caused by the cleanliness (oil, oxide) of the welding surface of the parent metal. There is also the purity of the gas, and there may be too much moisture in the gas. The purity of the gas may also be CO. The pores are mainly intensive and columnar because the CO2 gas used to protect the welding area from the air is mostly a byproduct of a winery or an alcohol plant and inevitably contains more or less moisture or other hydrogen. Substances, as well as argon in the gas mixture, also often contain moisture. If the total content of moisture and other hydrogen-containing substances in the shielding gas exceeds a certain limit, the generation of hydrogen pores in the weld metal will be inevitable.