V. I. Kravchenko

Stress-Strain State Evaluation of a Welded Joint of Hot Collector to Nozzle of NPP Steam Generator PGV-1000

The paper describes a method and main results of a refined stress-strain state evaluation for a welded joint of the hot collector to steam generator nozzle of a nuclear power plant with a WWÉR-1000 reactor, which takes into account a fuller range of the actual loading conditions in operation. In calculations, we considered the stresses induced by uncompensated thermal expansion of the reactor elements. The results of 3D finite element calculations suggest that the level of local stresses in the area of the joint exceeds the metal yield stress. The calculated stresses for the outer nozzle surface agree satisfactorily with the in-situ strain measurement data.

Stress-Strain State of the Coolant Collector-to-Nozzle Welded Joint in the PGV-1000M Steam Generator Under the Operating Loads with Consideration of Residual Manufacturing Stresses

Results are presented for both the calculated assessment of the residual manufacturing stress fields in the simulation of the heat treatment in the vicinity of welded joint No. 111, and the calculation analysis of operating stresses and the fracture resistance of the collector-to-nozzle welded joint in the PGV-1000M steam generator in the simulation of the operating loading cycle.

Peculiarities of the Fracture Strength Design of the Branch Pipe Zone of the Nuclear Reactor Vessel

The main methodological principles and the procedure of the refined calculation of the stress-strain state and fracture strength of the branch pipe zone of the reactor vessel under thermal shock have been formulated. A mixed scheme of the finite element method was taken as a basis of finite element analysis; it ensures continuous approximation both for displacements and for stresses and strains, which allows the fracture mechanics parameters to be determined with a high degree of accuracy. The paper presents the results of an elastic-plastic analysis of the fracture strength of the inlet branch pipe zone with an underpad crack in the simulation of the typical emergency core cooling conditions of a WWER-1000 reactor. The location and orientation of the postulated crack are substantiated to obtain the most conservative estimate of the fracture strength of the branch pipe. The calculations were performed with including the postulated crack in the finite element model of a fragment of the inlet branch pipe zone using the procedure of successive mesh thickening in the crack region. To determine the allowable critical temperature of brittleness of the branch pipe base metal, the tangent point, thermal crimping and descending branch approaches were used. According to the obtained results, the elastoplastic deformation of the metal and stress history affect the calculated estimate of the fracture strength of the branch pipe zone of the reactor vessel. It has been shown that the traditional linear elastic calculation, which is used to evaluate the fracture strength of the branch pipe, does not have sufficient degree of conservatism, which results in an exaggerated estimate of its strength.

Improving the Computational Analysis of Stress-Strain State and Fracture Resistance of Welded Joints Between Coolant Headers and PGV-1000M Steam Generator Vessel of Nuclear Power Station

The authors have outlined methodological principles and a procedure of performing the updated analysis of stress-strain state and fracture resistance of welded joints between coolant headers and PGV-1000M steam generator vessel. The paper gives the results of the elastic-plastic fracture resistance analysis of a welded joint containing variously shaped surface defects, in modeling a design operation cycle and an accident situation. According to the data obtained, the deformation loading history, residual technological stresses, and inclusion of surface damages have a significant effect on the design assessment of fracture resistance of a welding joint. It has been shown that the conventional linearly elastic calculation of fracture resistance of welded joints has an inadequate degree of conservatism and thus overestimates strength of the joints.

Stressed state of equal-diameter T-joints of pipelines under the action of torques and bending moments

We analyze the stressed state of pipeline T-joints in which the connecting pipe makes an angle of 90° or 45° with the main pipe under the action of torques and bending moments causing the out-of-plane torsion and bending of the T-joint. The influence of the angle of orientation of the connecting pipe on the behavior of the stress tensor is studied for various loading modes. For all investigated loading modes, we determine the stress concentration factors according to the Maxell-More theory of specific distortion strain energy.

Analysis of the stressed state in equal-diameter T-joints of pipelines. Part 1. Action of internal pressure and bending moments in the plane of a T-joint

We analyze the stressed state of two types of T-joints in which the union makes angles of 45° and 90° with the main pipe. The character of the distribution of stresses in a T-joint illustrates the distinctive features of its operation under the action of internal pressure and bending moments applied in the plane of the T-joint. On the basis of the theory of strength for specific distortion strain energy, we determine the stress concentration factors for all considered loading modes. The numerical values of the stress concentration factors are compared with the experimental data obtained by other authors.

Stress concentration in sloping cooling circuits of a disk of a gas-turbine engine

The stressed state and stress concentration in sloping cooling circuits of the rim part of a disk of a gas-turbine engine are studied by using a three-dimensional finite-element model. It is shown that the numerical values of the stress concentration factors do not exceed their designed values.