Estimating Long-Endurance Fatigue Strength of Girth-Welded Pipes Using Local Stress Approach

Nominal and hot spot stresses are conventionally used for fatigue design of welded joints. In this paper, use of local stress approaches was attempted to estimate the long endurance fatigue strength of girth welded pipes. Finite element modelling was carried out to determine the dependence of the stress concentration and through-wall stress distribution on weld root bead profile, with hi-lo values ranging from 0.25 up to 1.0mm. Two local stress approaches, critical distance and reference radius, were used to estimate the fatigue strength of girth welds at 5×10⁶ and 10⁷ cycles, which were then compared with available full-scale fatigue test results. To use the critical distance approach, the relevant material properties, such as threshold stress intensity factor range and fatigue limit for flush ground welds, were determined experimentally. This paper presents the results of the fatigue strength estimates and draws conclusions about the applicability of the local stress approaches to girth welds.