Microstructure and mechanical properties of welded joints of NPP pipelines after long-term operation

The microstructure and mechanical properties of welded joints of cuts from Du 300 and Du 500 pipelines of the Leningradskaya and Novovoronezhskaya nuclear power plants are studied after 70 and 100 thousand hours of operation. The effects of thermal aging simulating operational impact on the microstructure and properties of welded joints of the cuts and of a model coil are determined. It is shown that long-term operation can be accompanied by embrittlement and decrease in the crack resistance of the metal of welds in Du 300 and Du 500 pipelines produced from steels 08Kh18N10T and 08Kh18N12T. The discovered changes in the microstructure can lead to deterioration of the mechanical properties of the metal of welded joints in operation of Du 300 and Du 500 pipelines. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 36–42, July, 2006.