Zirconium alloy has good welding performance, stable chemical performance at room temperature, outstanding corrosion resistance, but its high temperature chemical performance is very active, has a strong affinity to environmental gases in oxygen, nitrogen, hydrogen, dust, humidity and other pollution in the operating environment. With the increase of temperature, its chemical activity increases sharply and forms ZrH2 with hydrogen at 200℃.ZrO3 can be formed with oxygen at 300℃.Above 550℃, porous brittle oxidation film was formed by reaction with oxygen in the air. At 600℃, zirconium absorbs nitrogen to form ZrN. Above 700℃, the absorption of oxygen leads to severe embrittlement of the material. With the increase of temperature, its absorption capacity and reaction speed increase. Therefore, the high temperature environment and welding seam produced by welding are the key to restrict chemical equipment.
The excellent corrosion resistance of zirconium alloy comes from the oxidation film formed on its surface, and depends on the integrity and firmness of the oxidation film. When the zirconium alloy absorbs a certain amount of oxygen, nitrogen, hydrogen and other gas impurities, its mechanical properties and corrosion resistance will decline sharply. The reaction generates porous brittle oxidation film. Therefore, the key factor of quality control in the welding process is to strengthen the protection of the surface of environmental dust, humidity and heat affected zone and the back of welding seam.
