| Popis: |
New structural materials that are light and durable are anticipated to reduce the running and maintenance costs of structures exposed to harsh marine environments, such as offshore oil production facilities, thereby reducing their lifecycle cost. This study aims to investigate the applicability of new materials to marine structures, focusing on their durability. To this end, a 5-year exposure test has been conducted from 1999 on 3 types of specimens (for corrosion observation, tension testing, and joint strength testing) made of 21 selected materials (6 nonferrous metals, 8 steels, 4 composite materials, and 3 rope materials). The specimens are exposed at 3 sites: Okinotori-shima and Miyako-jima, corrosive environments with high temperature and humidity, and a thermo-hygrostatic room in a laboratory. In 2004, the fifth and the last year of the ongoing exposure testing, the results of the observation and experiments of specimens recovered in 2003 after exposure for 4 years are subjected to analysis. The authors have already reported the detailed plan of the exposure test, initial performance of the specimens, and findings obtained each year from observation and testing. This paper primarily reports on the results of appearance observation of specimens at Okinotori-shima and Miyako-jima carried out in 2002, as well as the findings from observation and experiments on specimens exposed for 3 years at Miyako-jima. The state of corrosion at each site was grasped during the appearance observation. No appreciable difference was observed between the specimens exposed to natural environments at Okinotori-shima and Miyako-jima. Specimens recovered from Miyako-jima were subjected to appearance observation and experiments to grasp the state of corrosion. The strength of metal specimens that had shown strength losses a year earlier became even lower. Pitting corrosion increased on specimens on which surface corrosion had been found a year earlier. Also, surface corrosion was newly recognized on specimens of certain types on which no corrosion had been observed before. These phenomena indicate progress of corrosion due to exposure to natural environments. Comparison of these data with existing data of exposure to other natural environments revealed particular fierceness of the environments adopted for this study. |
