Ural Federal University (Ekaterinburg, Russia):

G. V. Shimov, Cand. Eng., Associate prof., Dept. of Metal Forming, e-mail: g.v.shimov@urfu.ru
Al. V. Serebryakov, Cand. Eng., Associate Prof., Dept. of Metal Forming

Pervouralsk New Tube (Novotrubny) Works (Pervpuralsk, Russia):
An. V. Serebryakov, Cand. Eng., Head of he group of new types of tubes for nuclear power industry, e-mail: andrey.serebryakov@chelpipe.ru

Steam generator is one of the main elements of NPP equipment. The failure of steam generators is a big problem for nuclear power. The average service life of heat exchange tubes of steam generators in Russia is currently 30-40 years. Increasing this lifetime is a very important task, as the design life of steam generators is approaching 60 years. Periodic repairs of steam generators, consisting in a partial “jamming” of heat exchange pipes, take a long time, lead to downtime of the equipment. During the operation of steam generators, the origin and subsequent development of corrosion defects of heat exchange pipes takes place, which can lead to the depressurization of the cooling circuits of the installation. The main reason for the appearance and development of corrosion damage of heat exchange tubes of steam generators, determining their service life, is the process of corrosion cracking of metal under stress. Corrosion cracking is the destruction of metals and alloys under the simultaneous influence of corrosive medium and tensile residual stresses arising in the surface layers of metal pipes in the process of their manufacture. Increasing resistance of heat exchanger tubing against intergranular corrosion, it is possible to do this in several ways. First, it is necessary to improve the quality of the pipe surface, as surface microdefects are places of origin of corrosion ulcers and cracks. In this regard, it is necessary to consider the option of replacing the technological operation of grinding heat exchange pipes to other, providing a higher surface quality, such as electrochemical processing. Second, the transition from 08Kh18N10T type steels to more corrosion-resistant high-alloy steels is possible. However, these measures can solve the problem of stress cor rosion cracking only from a part, as an important factor affecting the development of corrosion in pipes is the presence of residual stresses. Tensile residual stresses on the surface of the pipes contribute to the emergence and further growth (disclosure) of cracks, which leads to a rapid failure of the pipe. The absence of tensile residual stresses in the surface layers of pipes can reduce the risk of accidents and significantly increase the service life of steam generators to 60 years or more. In the article the method of calculation of residual stresses in the pipe wall, which allows the prediction of the residual stresses distribution over the cross section of the pipe wall, thereby to produce a preliminary assessment of the technology from the point of view of residual stresses in the finished product.

This work was carried out in the framework of the basic part of the State Assignment No. 11.9538.2017 / 8.9, supported by Program 211 of the Government of the Russian Federation (agreement No. 02.A03.21.0006).

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