Effect of pitting corrosion on local strength of hold frames of bulk carriers (1st report)

Firstly, pitting corrosion observed on hold frames in way,of cargo holds of bulk carriers which exclusively carry coal and iron ore has been investigated in detail. It was shown that the shape of the corrosion pits observed on them is a circular cone and the ratio of the diameter to the depth is in the range between 8 to 1 and 10 to 1, which is different from the trend observed for the bottom shell of the oil tanker where the ratio is in the range between 4 to 1 and 6 to 1. Secondly, a series of tensile tests has been conducted to investigate the effect of pitting corrosion on tensile strength of members. It was pointed out that the tensile strength decreases gradually and the total elongation decreases drastically with the increase of the thickness loss due to pitting corrosion. The reduction of the tensile strength of the members with pitting corrosion is larger than that of members with uniform thickness loss in terms of average thickness loss. Thirdly, a series of compressive buckling tests has been performed to examine the influence of pitting corrosion on buckling behavior of members. It was found that compressive buckling strength of pitted members is smaller than or equal to that of members with uniform thickness loss in terms of average thickness loss. Finally, an elasto-plastic analysis by FEM has been carried out to simulate the compressive buckling test in order to validate the method of modeling members with pitting corrosion. An attempt has been made to simulate the compressive buckling behavior of pitted members using shell elements of which meshing size is almost the same as the original thickness of the pitted plate. (C) 2004 Elsevier Ltd. All rights reserved.