Issue 49

R. Suresh Kumar et alii, Frattura ed Integrità Strutturale, 49 (2019) 526-535; DOI: 10.3221/IGF-ESIS.49.49 527 I NTRODUCTION ipings are critical systems in power plants and chemical industries. In coal-fired and nuclear power plants, these systems are subjected to many cyclic operating conditions during their service. It is known that cyclic loads exceeding specific magnitudes have a strong potential to cause crack initiation and propagation. However, in the case of Sodium-cooled Fast Reactor (SFR), where the piping system is made up of SS 316LN material, it is possible to detect sodium leakage, (i) due to the ductile nature of SS 316LN and (ii) elaborate sodium leak detection provision. These conditions made SFR design more favourable in demonstrating Leak-Before-Break (LBB) criteria [1]. In the case of SFR piping system, these conditions are respected as per the design criteria given in RCC MRx A16 [2]. The highly conservative method detailed in RCC MRx A16 poses challenges in demonstrating the LBB criteria for small-size low-pressure piping system. Conducting full-scale experiments at the required temperature on all the sizes of the piping system is expensive and time-consuming. Hence, there is a strong need for the development of a reliable numerical method for a quick and economical design of power plant components for LBB. This is the focus of the present paper wherein; benchmark analysis has been carried out towards validation of numerical Fatigue Crack Growth (FCG) simulation. It may be highlighted that the characteristics of FCG had been investigated by many researchers in the past [3-11]. In the present research, two representative geometries studied in the open literature [4-5] have been selected. The selected geometries are (i) a typical plate-type geometry with a specimen-type feature and (ii) a prototype pipe bend with the component feature. As already mentioned that an SFR piping system is subjected to cyclic bending stress variation during its service conditions [1]. The bending stress variation in the SFR piping system has a positive load ratio (R), which is defined as the ratio of the minimum stress (  min ) to maximum stress (  max ) during the cyclic load. Towards comparing the FCG behaviour of the specimen level plate-type geometry, data reported in [4] is used, and for the prototype geometric simulation, the full-scale pipe bend test data reported in [5] is used. B ENCHMARK DATA Plate specimen data hapuliot et al. [4] have investigated FCG behaviour in a plate specimen, by detailed experimentation. The geometric and loading details are given in Fig.1. The dimensions of the test specimen are 350 mm wide, 250 mm height and 20 mm thickness. An elliptical initial surface crack is provided at the centre of the plate as depicted in Fig.1. Figure 1: Geometric and loading of the plate specimen [4] The plate specimen is made up of SS 316 LN material. The essential data required for modelling the FCG behaviour of this geometry are presented in Tab. 1. P C   A   B