PSI - Issue 14

S. Vishnuvardhan et al. / Procedia Structural Integrity 14 (2019) 482–490 S. Vishnuvardhan / Structural Integrity Procedia 00 (2018) 000–000

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Keywords: Fatigue crack growth; corrosive environment; piping materials; ESE(T) specimen; fatigue damage

1. Introduction Structures such as offshore structures, bridges, power plant structures and aircraft which are subjected to repetitive environmental and operational loads are also exposed to corrosive environment during their service life. Estimation of corrosion fatigue crack growth rate is of great importance in life prediction and safety assessment of these structures. Horstmann et al (1995) studied the influence of environment and specimen geometry on fatigue crack growth in offshore structural steels with differing strength levels. The studies were carried out in air and in synthetic sea water under freely corroding and cathodically polarized conditions. The effect of frequency under cathodic polarization was found to be more pronounced in an aggressive environment. Fatigue crack growth (FCG) behaviour of two varieties of high strength low-alloy (HSLA) steels used in naval structural applications was evaluated in air and 3.5% NaCl solution by Sivaprasad et al (2006). The effect of stress ratio on air fatigue and corrosion fatigue crack growth (CFCG) behaviour was rationalised by the concept of crack closure and the effect of cyclic frequency on corrosion fatigue behaviour was also examined. Chinnaiah and Raghu Prakash (2010) conducted CFCG studies on Ni-Cr-Mn steel under 3.5% saturated NaCl aqueous environment. An increase in the crack growth rate and reduction in the threshold stress intensity for the material was observed in aqueous environment in comparison with that under laboratory air environment. Dong-Hwan Kang et al (2011) investigated fatigue and corrosion fatigue crack propagation (CFCP) behaviours of high-strength steel in air and seawater environments. Three-point bending fatigue tests were conducted under various loading conditions at different levels of loading frequency and load ratio. The CFCP rates in the seawater environment were higher than those in air condition under different loading conditions; the higher corrosion fatigue crack propagation rates was expected to be due to the mechanisms of hydrogen embrittlement together with anodic dissolution. Corrosion fatigue behaviour of a medium strength structural steel was studied in air and in 3.5% NaCl solution by Shu-Xin Li and Akid (2013). When compared to air, fatigue life in a corrosion environment was found to significantly reduce at low stress due to pitting damage, indicating a dominant role of corrosion over that of mechanical effects. The corrosion fatigue model proposed showed good agreement with the experimental test data at lower stress levels but predicted more conservative lifetimes as the stress increases. Huang et al (2008) carried out fatigue crack growth studies on compact specimens [C(T)] of A533B3 steels with four levels of sulfur content at different temperatures in air and high temperature water environments under constant amplitude cyclic loading. Fatigue crack growth tests under constant amplitude load were performed with a 100 kN closed loop servo-hydraulic machine at room temperature, 150 ºC, 300 ºC and 400 ºC. It was concluded that the fatigue crack growth rates in oxygen-saturated water environment were faster than those obtained in air. There was no significant difference between the fatigue crack growth rates for the steels with various sulfur contents and the fatigue crack growth rate at 400 0 C was about two and half times faster than those tested in room temperature, 150 ºC, and 300 ºC. Jamasri et al (2011) conducted fatigue crack growth studies on resistance spot-welded dissimilar material with significant difference in thickness between carbon steel and austenitic stainless steel. Carbon steel SS 400 with thickness of 3 mm and austenitic stainless steel SUS 304 with thickness of 1 mm were lap joined using resistance spot welding. Corrosion fatigue crack growth studies were carried out in air and seawater environments at a frequency of 8 Hz and salinity of 34.5 g/L. Results showed that corrosion fatigue strength of resistance spot-welded specimen in sea water environment was less than fatigue strength in air. The endurance limit in air was 32 MPa, whereas corrosion fatigue samples at this stress failed at about 400,000 cycles. Raghava et al (2014) and Vishnuvardhan et al (2015) carried out corrosion fatigue crack growth experiments on eccentrically-loaded single edge notch tension [ESE(T)] specimens made of IS 2062 Gr. E 300 steel. The corrosion process was accelerated using an external current source by applying constant Direct Current (DC) of 0.1 A, 0.2 A and 0.3 A. At each level of corrosion current three specimens were tested at a loading frequency of 0.25 Hz, 0.50 Hz and 0.75 Hz. Results showed that decrease in fatigue life varied from 14% - 42% when applied current increased from 0.1 A to 0.3 A. The effect of corrosion current on fatigue life was observed to be more predominant at higher frequencies, i.e., 0.50 Hz and 0.75 Hz when compared with 0.25 Hz. In the present studies, fatigue crack growth (FCG) experiments