Structural aspects of the environmentally assisted cracking of WWER 440 dissimilar weld joints

• Published in: The International journal of pressure vessels and piping 1996-08, Vol.68 (1), p.23-37
• Main Authors: Ruščák, M., Keilová, E., Kočík, J., Burda, J., Chvátal, P.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Fractures; Joining, thermal cutting: metallurgical aspects; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Nuclear reactors; Q1; Welding
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/0308-0161(95)00035-6

This paper deals with the environmentally assisted cracking assessment of the WWER 440 MWe (PWR type) reactor pressure vessel safe-end; this part of the primary circuit was tested in the framework of the LBB evaluation. The basic metallographic microstructures occurring in the weldment are described in detail. Particular attention is given to the ferrite-austenite transition region, containing microstructural elements which can embrittle the material during nuclear power plant service. CT specimens were loaded in both static and cyclic regimes in a high temperature primary circuit environment to assess the stress corrosion cracking and corrosion fatigue. The stress corrosion cracking tests showed negligible susceptibility to the crack initiation. It is shown that the fusion boundary may be a barrier which can effectively prevent the crack from growing under the static loading. The crack growth rate was in the range 10 −10 ms −1 which can not lead to critical crack propagation during the nuclear power plant operation. The results of corrosion fatigue tests showed that the fusion boundary is the weakest area of the weldment. Nevertheless, the kinetics are well below those shown in the published ASME XI curve.