Effect of Corrosion on Static Strength of Hull Structural Members (1st Report)

Influence of pitting corrosion on strength of steel ships and offshore structures

“…It has appeared that specimens with orderly located artificial pits which had a fixed diameter equal to the average pit diameter in actual corroded specimens could simulate the actual corroded specimen where the pit size and distribution are random. Results of standard static tensile tests of pitted and smooth specimens are described in [6,7,9]. Exemplary tensile diagrams (load versus displacement) for small specimens are shown in Fig.…”

“…Matsushita et al [6] realized tensile tests of specimens with different DOP from a single one-side pit up to more than 80% of two-side surfaces covered by pitting. Pitting corrosion causes not only unevenness of the material surface but reduction of the average thickness too.…”

“…If the only specimen of another type (wide specimen -type B) is not taken into account, the strength of pitted specimens for average thickness loss below 2 mm will be 527-600 MPa, while for average thickness loss above 2 mm [7] the strength will be 400-527 MPa thus it is not independent of the intensity of pitting. In spite of that, the maximum load that can be carried by a specimen can be approximately predicted by the above approach based on true fracture surface or minimum cross-sectional area [6,9]. The last conclusion concern so called small specimens.…”

“…Equivalent thickness of plates with pitting corrosion (t e ) for the tensile strength is almost equal to average thickness at the minimum cross section (t ave,min ) [10]: [6] t e = t ave,min…”

“…Web plates were pitted. It has appeared that for the following cases: (i) the ultimate strength is reached accompanying local buckling; (ii) the structural models collapse without buckling; (iii) shear buckling of web plates occurs; and (iv) web crippling occurs, equivalent thickness of the web plates can be predicted by equation (3) and the following equation: t el = 1.44 · t al (6) The above equations mean that the influence of the pittingcorrosion-induced unevenness of the plate surface on the ultimate strength of more complex structural models is more detrimental than for simple square plates.…”