PSI - Issue 60

Vivek Srivastava et al. / Procedia Structural Integrity 60 (2024) 233–244 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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CFCGR studies were conducted for this hull steel on machined compact tension (CT) specimens in accordance with the ASTM standard E647 (ASTM E647−13, 2014) . The sample was first pre-cracked to an additional crack growth of 2 mm in air at 15 Hz. Further this specimen was again pre-cracked with an additional growth of 1 mm in the corrosion medium (3.5 wt.% NaCl solution) at the test frequency of 0.1 Hz using sinusoidal fatigue loading waveform. Next, CFCGR test was carried out at the load ratio of 0.1 and test frequency of 0.1 Hz and, which typically depict the sea wave loading conditions on a ship hull structure. CFCGR experiments were conducted both under unprotected FC condition as well as under ICCP condition. ICCP condition was applied at a protection potential of (-) 800 mV. Load ratio (R), the ratio of minimum to maximum load in a corrosion fatigue cycle, was 0.1. These tests were carried out using a CORTEST-make electro-mechanical motor based horizontal corrosion fatigue test equipment. ICCP setup was deployed using a GAMRY Ref 3000 model Potentiostat, its electrode terminals and a control PC. A wire was soldered to CT specimen and connected to the first terminal of the potentiostat. CT specimen acted as working electrode. An external platinum electrode was connected for pumping current and acted as counter electrode. A standard calomel electrode (SCE) was also connected, which acted as a reference electrode. Fig. 3(a) shows the photographs of CT specimens for FC (unsoldered) and ICCP (soldered) tests. Fig. 3(b-c) shows the corrosion fatigue test and ICCP setups used to conduct CFCGR studies. Ambient (air) test temperature was 27 o C and that for corrosion medium was 25 o C. Compliance method was adopted for crack length (a) measurement from the slope of unloading part of the load displacement raw data of cycles. The slope was normalized with modulus of elasticity (E) and thickness (B) and converted to crack value using equations described in ASTM E647 standard (ASTM E647−13, 2014) . Stress intensity ranges (∆K) was calculated from applied load range (∆P) and crack using relevant equations in the standard.

Fig. 3(a). CT specimens used for CFCGR test in FC and ICCP conditions

Fig. 3(b): Corrosion fatigue test setup with CFCGR test specimen (CT) and ICCP system