Main methods to prevent porosity in welding process of pressure vessel

1. Process measures

(1) Eliminate the source of various gases. Remove the oxide film or rust, dry the welding rod and flux according to the regulations and store them reasonably, and remove the oxygen, hydrogen and nitrogen in the protective gas.

(2) Strengthen protection. The coating of the electrode should not fall off, the supply of flux or shielding gas should not be interrupted, the arc should not be arbitrarily elongated, and the assembly gap should not be too large. When using a low-hydrogen type electrode, short arc and DC reverse connection should be used.

(3) Correctly master the welding operation process. Create favorable conditions for gas floating in the molten pool, and preheat if necessary.

2. The metallurgical measures are to select the electrode flux that is compatible with the base metal.

(1) The oxidant and deoxidizer in the covered flux are properly matched. Properly increasing the oxidizing property when welding low carbon steel can reduce the porosity caused by hydrogen gas; and appropriately increasing the deoxidizing property when welding high carbon steel can reduce the porosity caused by CO.

(2) Appropriate addition of alloying agent and slag-forming agent in the flux can reduce porosity, such as appropriate addition of SiO2, MnO, MgO can reduce porosity.

(3) Adjusting the viscosity of the flux, adding some CaF3 or TiO2 appropriately is an effective method to reduce the viscosity, which is conducive to the escape of gas in the weld.