Fatigue Crack Propagation Properties of Cathode Potential Charged Ti-6Al-4V Alloy in Seawater-1st Report: Study on Materials Selection of Marine Riser for Deep Sea:—1st Report: Study on Materials Selection of Marine Riser for Deep Sea

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The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) is planning scientific riser drilling for 4, 000 meters depth class risers in the future by utilizing the riser drilling vessel "Chikyu". There are many technological problems in order to realize this plan, and it is very important to reduce the self weight for riser pipes in the deep sea. Titanium alloy with high specific intensity is considered to be a potential material of marine riser for the deep sea. Not much is known about the mechanical properties of titanium alloy as it is an industrially new material for marine riser, and in particular fatigue crack propagation properties are not enough.<BR>In this study, by using center notched specimens of Ti-6Al-4V alloy (ASTM Grade 5), fatigue crack propagation tests were carried out under constant amplitude loading in the air, seawater and seawater for charging the cathode potential of -0.8V (vs. SCE) and -1.2V (vs. SCE) on specimens. As a result, it became clear that fatigue crack propagation rate is influenced by the stress ratio and the cathode potential, though Ti-6Al-4V alloy shows a superior corrosion resistance in seawater.