The reduction in fatigue strength of welded joints in sea-water, as compared to air, found in various National test programmes has been shown to vary quite widely. The results have therefore been examined, and additional tests have been carried out, to try to determine the reasons for the variability. As a result some correction factors have been derived and the results have been re-analysed, on the basis of which revised environmental reduction factors are proposed.
The current Department of Energy design guidance for offshore structures (Dept. Energy, 1990) indicates that, for unprotected steel joints in sea-water» the fatigue life is reduced by a factor of 2·0, whilst cathodic protection at the optimum potential restores the life to that measured in air. These recommendations are based on extensive fatigue tests conducted on plate specimens, within the United Kingdom Offshore Steels Research Programme UKOSRP 1 (Dept. Energy, 1988). Further tests have been conducted since the Guidance Notes were drafted in the early 1980's, and a Review Panel has been examining these to establish whether the guidance should be modified. A compilation of data obtained in a number of studies, including UKOSRP, has recently been prepared by Sharp and Thorpe (1988) and is shown in Fig. 1. Since the UKOSRP tests were carried out in two separate laboratories, whose results were in broad agreement with each other, it is clear that the differences outlined above are not attributable to testing techniques in a single laboratory. The results are given in a slightly different form to that used by Sharp and Thorpe. They compared the lives corresponding to particular stresses and presented the results in terms of the environmental reduction factor (ERF), which was defined as (life in air/life in sea-water) for a particular stress range.
