Fatigue crack growth of EH36 steel in air and corrosive marine environments

Abstract

EH36 steel used in offshore platforms is susceptible to corrosion fatigue in marine environment. The corrosion fatigue performance in EH36 steel is influenced by various factors, such as maximum applied load, loading frequency and stress ratio. To investigate such effects, fatigue crack growth (FCG) tests on compact tensile (CT) specimens of EH36 steel were carried out in three different environments, including air, immersed seawater and wet-dry cyclic environment, by considering different maximum loads, loading frequencies and stress ratios. From the experimental tests, the relation of crack development and loading cycles and the relation of fatigue crack growth rate (FCGR) and stress intensity factor (SIF) range were obtained. Constants (C and m) in Paris law were obtained through fitting technique based on experimental data. Due to corrosion of marine environment, the fatigue life of EH36 steel decreases while the FCGR increases. The corrosion fatigue crack growth (CFCG) experimental results were compared with the predictions from Paris-law recommended in BS7910. A new CFCG calculation model consisting of environmental acceleration factors was proposed and evaluated for accuracy, and such model can be used for predicting the remaining fatigue life of EH36 steel in marine corrosive environment under the specified conditions. The fracture morphology of the specimens in different environments was observed by scanning electron microscope (SEM) to analyze the fracture mechanism. The fracture morphology of the CT specimens in two corrosive environments is almost same and appears as cleavage fracture.