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Fatigue Crack Growth Assessment in Underwater Wet Welds

Content Provided by: Welding Journal, An American Welding Society Publication (AUGUST 2017)

Abstract: The characteristics of fatigue crack propagation of welds produced with underwater wet welding were evaluated out of water. Butt joints were produced in a hyperbaric chamber at simulated depths of 10, 60, and 90 m. A gravity welding system was used to deposit a AWS E6013 commercial electrode coated with vinylic varnish. Welding joints were prepared from an A­36 plate, 19 mm thick, with 45­deg V­grooves filled with an average of 18 passes. The fatigue crack growth rate properties in the near threshold and Paris regimes for the weld metal were determined by using compression precracking followed by load reduction and constant amplitude test procedures. Mechanisms of crack propagation were investigated on the fracture surface by means of a scanning electron microscope and confocal laser scanning microscopy. Lateral surface observations, considering different loading conditions, were made using optical microscopy. The resulting fatigue crack growth rates were shown to depend on pore density that varies with the depth at which underwater wet welding was performed. The fatigue crack growth path showed a branched morphology, which is a consequence of the interaction between cracks and pores. The results of this study show that underwater wet welding procedures produced fatigue­resistant weld metal that is adequate for use at low applied stresses in structures, in agreement within design codes.

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