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

• 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.

#### File

Fig. 1 System analysis phase in the system life cycle

Fig. 2 V-model for SG life cycle

Fig. 3 IDEF0 diagram

Fig. 4 N2 diagram

Fig. 5 EFFBD diagram

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

Fig. 7 Tube-tubesheet geometry configuration

Fig. 8 2D axisymmetric model

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

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

Fig. 11 Contact pressure distribution

Fig. 12 Expansion pressure optimization

Table 1 Tube and tubesheet geometry specifications (1)

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

#### Acknowledgement

Supported by : Kepco International Graduate School (KINGS)

#### References

1. Korea Electric Power Research Institute (KEPRI), 2014, APR1400 SSAR - Chapter 5. Reactor coolant system and connected system, Korea.
2. INCOSE-TP-2003-002-04, 2015, System Engineering Handbook, Guide for System Life Cycle Process and Activities, 4th edition. John Wiley and Sons. Inc., Hoboken New Jersey, USA.
3. Kossiakoff, A., Sweet, W. N., Seymour, S. J. and Biemer, S. M., 2003, Systems Engineering Principles and Practice, A John Wiley & Sons, Inc. Publication, New Jersey, USA.
4. Harvey J. F., 1987, Theory and design of pressure vessels, Van Nostrand Reinhold Co., New York.
5. ASME Boiler and Pressure Vessel Code, Sec. II, 2010, "Material Properties", American Society of Mechanical Engineers, New York.
6. Kweon H.D., Heo E.J., Lee H.D., and Kim J.W., 2018, "A methodology for determining the true stress-strain curve of SA-508 low alloy steel from a tensile test with fine element analysis," Journal of Mechanical Science and Technology., Vol. 32, No. 7, pp. 3137-3143. https://doi.org/10.1007/s12206-018-0616-8
7. Bouzid A. H., Mourad A. I. and Domiaty A. E., 2016, "Influence of Bauschinger effect on the residual contact pressure of hydraulically expanded tube-to-tubesheet joints," International Journal of Pressure Vessel and Piping., Vol. 146, pp. 1-10. https://doi.org/10.1016/j.ijpvp.2016.07.002
8. Allam M. and Bazergui A., 2002, "Axial Strength of Tube to Tubesheet Joints: Finite Element and Experimental Evaluations," Journal of Pressure Vessel-Technology, ASME, Vol. 124, No.1, pp.22-31. https://doi.org/10.1115/1.1398555
9. Kohlpaintner W. R., 1995, "Calculation of Hydraulically Expanded Tube-to-Tubesheet Joints," Journal of Pressure Vessel-Technology, ASME,, Vol. 117, No.1, pp. 24-30. https://doi.org/10.1115/1.2842086
10. Bergant, M., Yawny, A. and Perez-Ipina, J., 2017, "J-resistance curves for Inconel 690 and Incoloy 800 nuclear steam generators tubes at room temperature and at $300^{\circ}C$," Journal of Nuclear Materials, Vol. 486, pp. 298-307. https://doi.org/10.1016/j.jnucmat.2017.01.040