Russian nuclear goiant ROSATOM announced that welding of the main coolant pipeline has commenced at Kudankulam NPP Unit 3 in India. This stage continues construction of the power unit after installation of the reactor pressure vessel (April 2022) and dome closing (November 2022). MCP welding is a complex process operation which covers 16 pipe units and includes several stages: preparation, welding-up, heat treatment, non-destructive testing, austentic surfacing, performed by the highly-qualified personnel. The total MCP length is about 140 m, pipe wall thickness is 70 mm, the total length of 28 welded joints is over 87 m.MCP is a part of the primary coolant circuit along with the reactor and four circulation loops, each of which, in its turn, includes the steam generator, reactor coolant pump set and main coolant pipelines connecting the loop equipment with the reactor and steam generator. The design service life of MCP in tough environment (pressure 160 atm., temperature 3500С) is 60 years.Timely completion of MCP welding in conjunction with the installation of thermal and mechanical equipment determines the commencement of flushing to the open reactor and the stage of hydraulic tests and circulation flushing of the primary circuit.