ВИЗНАЧЕННЯ ТЕХНОЛОГІЧНИХ ОСОБЛИВОСТЕЙ ЛАЗЕРНОГО ЗВАРЮВАННЯ СТИКОВИХ З’ЄДНАНЬ З РІЗНОРІДНИХ НЕРЖАВІЮЧИХ АУСТЕНІТНИХ СТАЛЕЙ У ВЕРТИКАЛЬНОМУ ПРОСТОРОВОМУ ПОЛОЖЕННІ

Abstract

The problem of repair of collectors of steam generators of nuclear power plants (NPPs) has become extremely urgent today. The way of pressurization of heat exchange tubes by plugs is promising, provided the quality of the joints is high. Practical experience in the use of welding to solve this problem has shown the need to find technological solutions related to increasing the depth of penetration and reducing the thermal impact area. The purpose of the work was to determine technological features of laser welding of joints of heterogeneous stainless austenitic steels in vertical spatial position with subsequent application of the results to solve the above problem. Two technological options for plugs welding in using rectilinear and annular butt joints in vertical position with different weld shape factors have been proposed. Laser welding modes have been worked out and samples of welded joints have been made. According to the results of the analysis of the data of mechanical tests, visual and radiographic control, tightness tests and metallographic studies, the appropriate modes of laser welding of plugs for each of the two options have been determined. The annular butt welded joint of the type "plate-pipe" of 10X18H10T (pipe) and 10X17H13M3T (plate) steels, made in vertical position, was the main type. Static tensile test data indicate that for welds with a joint ratio of greater than one, a fracture force of about 11% higher is achieved compared to joints of less than one. The main causes of defects in laser welding of annular welded joints of heterogeneous stainless steels are revealed and the ways of their elimination and prevention of their appearance are offered. Principal technological techniques of laser welding of annular welded joints of heterogeneous steels in different spatial positions have been developed. On the basis of the results of the conducted researches technological recommendations on laser welding of plugs in heat exchange tubes of the collector have been formulated, which will significantly improve the technology of repair of steam generators of nuclear power plants.