In the pre-fabrication stage of a large number of welding joints, it is necessary to set up a special enclosed clean site and strictly control the dust pollution and air humidity in the environment. For example, clean labor protection shoes should be changed when entering the construction site to ensure the cleanliness of the welding environment. In the outdoor installation environment, make temporary operation room to achieve clean conditions. It is an important factor to ensure the welding quality to strengthen the requirements of welding joint groove, groove on both sides within 70mm and the cleanliness of welding wire surface.
Porosity is the most common defect in zirconium alloy welding. The pores are mostly concentrated near the fusion line and the center line of welding seam. The key to prevent welding porosity defects is to strengthen the control of welding environment cleanliness and humidity, to strengthen the cleaning of groove and welding material surface, and to improve the internal and external protection quality of high purity argon in the welding zone.
Due to the low thermal expansion coefficient of zirconium alloy, small thermal deformation and volume change during phase change, low content of sulfur, phosphorus, carbon and other impurities in zirconium alloy, no obvious tendency of crack formation in the welding process. However, when the welding seam absorbs a certain amount of oxygen, nitrogen and hydrogen gas impurities during the welding process, the properties of the welding seam and the heat-affected zone will become brittle. If there is stress in the peer links of the welding seam, cold cracks will occur. At the same time, hydrogen atoms have the property of diffusing and accumulating to the high-stress parts in the heat-affected zone of lower temperature, which promotes the formation of relatively weak links in these parts, and thus may lead to the generation of delayed welding cracks.
In the welding test, the manual tig welding with low welding line energy and convenient welding seam gas protection should be selected. In order to prevent the welding seam from being oxidized and absorbing the harmful gas, air isolation is carried out by using the welding nozzle with larger diameter, the outer surface protection cover of welding seam and argon filling inside the pipe. The filler wire used in zirconium alloy welding should be selected according to the principle of matching with the base material composition. The surface of welding wire shall be free from defects such as heavy skin, crack, oxidation and metallic or non-metallic inclusion. The wire should be cleaned and dried before use.
