The AWS-X “hotspot stress-load cycle” curve used at present for designing tubular joints is based mainly on the fillet-welded plate test data and some more data from small-scale tests on tubular joints, which were available in the early 1970s. A review of further tests carried out in the recent years, including those by the authors, leads to the conclusion that the influence of the diameter and thickness of the tubes plays a significant role in the joint fatigue behavior. Hence, they must be taken into consideration while designing tubular joints accurately and more economically. A modified design method is proposed here with design curves for four diameter values. Further, the results of fatigue tests on K-type joints investigating the effect of stress ratio R and of post-weld heat treatment on the joint fatigue strength are described in this paper.

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