Nuclear Engineering and Design 241 (2011) 464–470 Contents lists available at ScienceDirect Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes Evaluation of tube to collector connection by hydraulic expansion method in PGV-1000 steam generators H.G. Dashti, B. Hashemi ∗ , S.A. Jahromi Department of Material Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran article info Article history: Received 22 May 2010 Received in revised form 8 November 2010 Accepted 23 November 2010 abstract Investigations on steam generators failure due to cracking in collector ligaments at perforated parts deter- mined that connection process of the tubes to collector could be one of the main breakdown causes. The stability and strength of tube to collector joint is dependent to the geometry of tube and collector, the joining process and the operational conditions. In this research hydraulic expansion method has been considered as connection method of tube to collector. The Finite Element Method (FEM) was used to sim- ulate the hydraulic expansion process and determine stress condition of the joints. The contact stresses between the tube and collector interface were modeled using contact elements of ANSYS program. Fur- thermore, the effect of clearance between tube and collector on the residual stresses around of joints was investigated. Some specimens from collector and tube materials were tested at various temperatures and their results were used at rate-independent multi-linear Mises plasticity model for FE analysis. Required connection strength between tube and collector is estimated based on ASME rules and compared with FE results. The results show that the residual tensile stresses could be greatly increased by decreasing of initial clearance. The highest value of residual stresses was observed around of collector holes neverthe- less it was considerably lesser than obtained residual stresses in explosive method. The contact pressure and other parameters were in allowable ranges and the friction stresses were negligible. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Steam generator (SG) integrity and reliability is one of the most complicated issues of Nuclear power plants (NPP) and should be considered during design, manufacturing and operation of both horizontal (HSG) and vertical steam generators (VSG) (Bergunker, 2006; Berezanin, 2009). In the recent years this problem has been investigated from mechanical, chemical and metallurgical aspects (Bergunker, 2006; Berezanin, 2009; Bakirov et al., 2006; Trunov et al., 2008). However in this paper only certain mechanical issues are investigated. Though it is confirmed that HSGs has higher reli- ability and operability, compared with VSG, by its nature of design and recent corrections (Bergunker, 2006; Berezanin, 2009; Bakirov et al., 2006) however analysis should be performed to ensure the effectiveness of corrective actions. The damage of perforated collector ligaments (above the non- perforated zone) is one of the main HSG failures, which may occur due to fatigue, low temperature creep, strain ageing and concen- tration of admixtures in Gap of collector and expanded tubes. All mentioned parameters are in combination with high residual stress fields. The high value of residual stresses due to explosive ∗ Corresponding author. Tel.: +098 0711 6133399; fax: +098 0711 2307293. E-mail address: b hashemiz@yahoo.com (B. Hashemi). expansion process might be resulted in strain ageing and low tem- perature creep, which accelerates the subcritical crack growth in the secondary circuit environment and causes the failure of SG at connection area of tube to collector (IAEA, 1994). The replacement of explosive expansion process with hydraulic expansion method accompanied by mechanical rolling has been performed as a solu- tion to reduce residual stresses. Rolling, explosive expansion and hydraulic expansion are three connection methods of tube to collector. Among these methods, hydraulic expansion method is more convenient because of its abil- ity in measuring and controlling of the expansion pressure. In this method hydraulic pressure is exerted inside the tube walls until the tubes uniformly expands in collector holes. Many studies have been devoted to evaluate this connection method. Scott et al. (1984) investigated residual stresses and mechanical behavior of tubes in transition region of tubes (Fig. 1). Weinstock et al. (1987) presented some results about the relia- bility of expansion process. Some analytical calculation and finite element analysis have been done which mainly focused on axial strength of tubes (Yokell, 1982; Jawad et al., 1987). Recently Wang et al. (2007) performed analytical FE calculations on connection strength of hydraulic expansion connections. Strength and stability of tubes and joining especially in the transition region of connection have been considered in all of these studies. However, evidences show that some particular failures are experienced at collector 0029-5493/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2010.11.020