[en] Full text: In October 2016, MHI completed the replacement of pressurizer safe end weld in Ringhals unit 3, which was the first maintenance work for main component of PWR plant in Europe. For higher reliability and longer lifetime of PWR plant, MHI has conducted many kinds of maintenance works of main components of PWR plants in Japan against stress corrosion cracking due to aging degradation. MHI has completed this work in 21 PWR units in Japan. That of Ringhals unit 3 was planned and conducted based on the experiences. It was proved that the replacement of pressurizer safe end weld can be applied to overseas plants in the same way for plants in Japan. In this work, the nickel-base alloy 600 used for nozzles of pressurizer was replaced to nickel-base alloy 690. The nickel-base alloy 690 is more corrosive-resistant than nickel-base alloy 600. So that, the risk of stress corrosion cracking due to the aging degradation of the nickel-base alloy 600 is reduced by this work. The following two technologies are critical to establish replacement of pressurizer safe end welds. -Buttering weld of alloy 690 on site -Post weld heat treatment for buttering weld on site These two technologies are introduced through the application of Ringhals unit 3. The procedure of buttering applied to Ringhals unit 3 was established following process: 1) Planning of welding procedure and acquisition of welding procedure certification 2) Qualification for applicability of welding procedure by using mock-up 3) Training for welders The procedure of post weld heat treatment applied to Ringhals unit 3 was established following process: 1) Feasible study with thermal analysis 2) Qualification for applicability of post weld heat treatment using mock-up 3)Traing for heat treatment personnel. (author)