Fatigue studies on stainless steel piping materials and components: Indian AHWR

Abstract

As a part of component integrity test program at Bhabha Atomic Research Centre, fatigue tests on full scale pipe and pipe welds were conducted in addition to CT and TPB specimens. In this paper the outcome of this program is discussed. Specimen testing was conducted to determine the basic cyclic stress strain curve, LCF and FCGR properties. FCGR tests were conducted on CT and TPB specimens to understand the effect of different conditions: Specimen level tests result show that, for the present grade of material, the FCGR is not significantly affected by specimen type (CT and TPB), specimen thickness and notch orientation. FCGR resistance of the hot wire GTAW is superior compared to that of conventional SMAW. The effects of stress ratio are mildly significant at lower R-values for base metal but are significant for weld metal. Component tests were conducted to understand the effect of the following variables:(a)Component type and size: pipe and pipe weld, Pipe diameters 170 mm and 324 mm,(b)Pipe and pipe weld: initial notch in pipe base, and girth welded pipe, (c) Pipe welds: Conventional GTAW/SMAW and hot wire narrow gap GTAW, (d)Environment: Air and water, (e) Type of loading: Constant amplitude cyclic, vibration, Block, overload and underload. Results indicated that the fatigue life of the component is reduced under water environment compared to air environment. Fatigue life of the pipe subjected to block loading (increasing stress ratio followed by decreasing stress ratio), intermittent overloading and underloading is also decreased compared to that of constant amplitude loading. Vibration loading reduces fatigue life significantly. Crack growth in thickness direction is more compared to circumferential direction for all types of loading which is desirable for demonstration of LBB criteria. Fatigue life of the notched component has also been predicted using the Paris constants data from the specimen level tests. Fatigue crack growth and the crack shape of the growing crack have been evaluated for regular interval of loading cycles. The predictions compares well with those of experiments.