2023 №03 (04) DOI of Article
2023 №03 (06)

Automatic Welding 2023 #03
Avtomaticheskaya Svarka (Automatic Welding), #3, 2023, pp. 27-38

Mathematical modeling of residual stresses in a composite welded joint of the collector adapter sleeve to the branch pipe of ZPM-440 steam generator

A.A. Makarenko1, O.V. Makhnenko2

1STC of E.O. Paton Electric Welding Institute of the NAS of Ukraine, 11 Kazymyr Malevych Str., 03150, Kyiv, Ukraine.
2E.O. Paton Electric Welding Institute of the NAS of Ukraine. 11 Kazymyr Malevych Str., 03150, Kyiv, Ukraine. E-mail: office@paton.kiev.ua

Composite welded joints of dissimilar materials, usually steel of ferrite-pearlite (bainite) and austenite classes were used in elements of equipment and pipelines of operating nuclear power plants (NPP). The considerable difference in chemical composition of base material and welding consumables leads to chemical and structural inhomogeneity of metal in the joint zone, and the difference in the coefficients of thermal expansion of the materials during welding and postweld heat treatment results in formation of high unrelaxed residual stresses, which significantly influence the strength, fatigue life and corrosion resistance of equipment elements. Considerable difficulties of experimental measurement of residual stresses make it complicated to take them into account at determination of the service life of nuclear power plant elements. Damage of the Dn-1100 welded joint in the welded assembly of the coolant collector adapter sleeve from 08Kh18N10T stainless steel and the branch pipe of the steam generator body from 22K steel is one of the problems in safe operation of WWER-440 nuclear power units. In this connection, the methods of mathematical modeling were used to perform analysis of the microstructural phase composition and residual stresses, arising in this joint in welding, and of their influence on the service life of the welded assembly. Analysis of the results of mathematical modeling of the thermal processes, microstructural phase transformations and stress-strain state (SSS) in the composite welded joint showed that hardened structures in the HAZ of branch pipe metal (St22K) and lowering of the material crack resistance characteristics can be found at violation of surfacing and welding technology during steam generator manufacture, namely non-compliance with the conditions of preheating and concurrent heating (T ≥ 200 °C). Rather high residual tensile stresses were determined on the composite joint inner surface, which is in contact with the coolant corrosive medium in operation, as well as in the zone of contact (fusion) of the material of branch pipe pearlitic steel to austenitic metal of the weld, where there is a high probability of discontinuity defect formation in welding. It may have a negative influence on the strength and structural integrity of the welded assembly of branch pipe of steam generator (SG) at further long-term service. 17 Ref., 15 Fig.
Keywords: composite welded joint, PGV-440 steam generator, heat-affected zone, microstructural phase transformations, residual stresses, mathematical modeling

Received: 08.03.2023


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