Abstract
The nucleation mechanism of corrosion cracks in welded structures in natural seawater has been revealed through investigation on the corrosion behavior of X65-welded structures in natural seawater. The evolution laws of surface corrosion morphology, residual stress, and areas of welded structures with the most serious corrosion damage were analyzed by microstructure observation, corrosion morphology observation, residual stress detection, and magnetic field detection. The results show that the main factors of determining surface corrosion morphology evolution law of welded structures are microstructures of the weld joint, heat-affected zone (HAZ), and the fusion line. Due to the difference of corrosion rates between the weld joint, HAZ, and the coarse Widmänstatten structure in fusion line, the fusion line of welded structures receives the most serious damage while being corroded. Meanwhile, mutual reinforcement of residual stress and corrosion damage on the surface of welded structures further accelerate the nucleation of corrosion cracks. Under the influences of microstructure, residual stress, and corrosion, corrosion cracks that are parallel to weld joints generate first in the fusion line of welded structures. Therefore, it makes welded structures the source of marine steel structures’ corrosion failure.
Highlights
Due to the good connection performance and excellent air tightness, welding fabrication has been applied in the manufacturing of marine steel structures such as drilling platforms and seabed pipelines [1,2,3,4]
Corrosion crack nucleation mechanism of welded structures in natural seawater is revealed by microstructure observation and the conclusions are as follows: (1) While serving in natural seawater, microstructures of the weld joint, heat-affected zone (HAZ), and the fusion line are the main factors in determining surface corrosion morphologies and evolution process in all areas
Continuous corrosion grooves are formed, which are caused by two aspects: one is the di erence of corrosion rates between the weld joint and HAZ near the fusion line, the other is the coarse Widmanstatten structure in the fusion line
Summary
Due to the good connection performance and excellent air tightness, welding fabrication has been applied in the manufacturing of marine steel structures such as drilling platforms and seabed pipelines [1,2,3,4]. Welded structures will always be high-risk areas for the occurrence of corrosion crack in the sea and source of corrosion failure of marine steel structures [5,6,7,8]. With international investment increasing in marine projects, corrosion protection of welded structures in the marine environment has been a focus of research [9,10,11,12]. Erefore, to prevent the occurrence of corrosion failure accidents of welded structures in the marine environment, research on the corrosion crack nucleation mechanism of welded structures in the marine environment needs to be carried out. Little research is dedicated to the nucleation mechanism of corrosion cracks in welded structures. Theories such as hydrogen-induced cracking and anodic dissolution can reveal the corrosion crack nucleation mechanism of nonwelded structures to some extent [28,29,30,31], such traditional theories are not sufficient to reveal the nucleation mechanism of corrosion cracks in welded structures because of the particularities in terms of crystal structure and residual stress distribution of welded structures
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