Comportamento a fatica in acqua di mare di un acciaio per strutture offshore in presenza di difetti acuti

The aim of this research was to study the effect of sea water on the fatigue behaviour of a steel (API 5L grade X65) commonly used in offshore environments, in the presence of sharp defects. Experiments have been carried out in air and in synthetic sea water, under conditions of both free corrosion and cathodic protection, with the ratio sigma min/ sigma max equal to 0. 1 and 0. 6. Moreover, at the latter value, tests have been carried out in a 3. 2% NaCl solution. Besides the experiments carried out increasing the stress intensity factor range, other tests have been carried out decreasing it, in order to take measurements at low levels of the above factor. During the fatigue tests, the crack length has been measured automatically, using the rigidity method arranged for this purpose. Results have been explained on the basis of recent models suggested for the corrosion-fatigue phenomenon.