Corrosion Fatigue-Cracking Behaviors of Low Alloy Steels in Seawater for Offshore Engineering Structures

Abstract

The fatigue crack growth (FCG) properties of offshore engineering structural steel DH36Z35 were studied in air and an artificial seawater environment. Results show that the FCG rate in seawater is up to 134.5 pct higher than in air. The test results of FCG rate in air and seawater at different frequencies show that FCG in seawater is accelerated compared with that in air at frequencies below 7 Hz. The lower the frequency, the more obvious the acceleration. It is found that the larger the seawater flow rate, the larger the corrosion fatigue crack growth (CFCG) rate. Compared with static seawater, when the flow rate reaches 180 L/h, the average increase of CFCG is about 55.6 pct. In addition, the mechanism by which corrosion accelerates fatigue crack propagation is analyzed from three different perspectives: corrosion product morphology, crack propagation path and corrosion electrochemistry.

Effect of corrosion on the fatigue crack propagation properties of butt weld with G20Mn5QT cast steel and Q355D steel in 3.5‐wt% NaCl solution

“…Zhao et al 3 studied the corrosion fatigue crack initiation mechanism of X80 steel in the marine environment and showed that, in addition to the influence of stress concentration caused by corrosion pits, corrosion products attached to the metal surface will also promote the initiation of corrosion fatigue cracks. Liu et al 4 studied the FCP performance of offshore engineering structural steel DH36Z35 in air and artificial seawater environments. The results indicated that the FCP rate in seawater is 134.5% higher than that in air.…”