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Evaluation of APR1400 Steam Generator Tube-to-Tubesheet Contact Area Residual Stresses

  • Received : 2018.11.26
  • Accepted : 2019.06.17
  • Published : 2019.06.30

Abstract

The Advanced Power Reactor 1400 (APR1400) Steam Generator (SG) uses alloy 690 as a tube material and SA-508 Grade 3 Class 1 as a tubesheet material to form tube-to-tubesheet joint through hydraulic expansion process. In this paper, the residual stresses in the SG tube-to-tubesheet contact area was investigated by applying Model-Based System Engineering (MBSE) methodology and the V-model. The use of MBSE transform system description into diagrams which clearly describe the logical interaction between functions hence minimizes the risk of ambiguity. A theoretical and Finite Element Methodology (FEM) was used to assess and compare the residual stresses in the tube-to-tubesheet contact area. Additionally, the axial strength of the tube to tubesheet joint based on the pull-out force against the contact joint force was evaluated and recommended optimum autofrettage pressure to minimize residual stresses in the transition zone given. A single U-tube hole and tubesheet with ligament thickness was taken as a single cylinder and plane strain condition was assumed. An iterative method was used in FEM simulation to find the limit autofrettage pressure at which pull-out force and contact force are of the same magnitude. The joint contact force was estimated to be 20 times more than the pull-out force and the limit autofrettage pressure was estimated to be 141.85MPa.

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Fig. 1 System analysis phase in the system life cycle

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Fig. 2 V-model for SG life cycle

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Fig. 3 IDEF0 diagram

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Fig. 4 N2 diagram

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Fig. 5 EFFBD diagram

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Fig. 6 Elastic and plastic regions in thick-walled cylinder

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Fig. 7 Tube-tubesheet geometry configuration

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Fig. 8 2D axisymmetric model

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Fig. 9 SA-508 Gr.3 Cl.1 plastic stress-strain curve (6)

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Fig. 10 Alloy 690 stress-strain curve (10)

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Fig. 11 Contact pressure distribution

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Fig. 12 Expansion pressure optimization

Table 1 Tube and tubesheet geometry specifications (1)

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Table 2 Material properties of Inconel 690TT and SA-508 Grade 3 Class 1 (5) (6)

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Acknowledgement

Supported by : Kepco International Graduate School (KINGS)

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