Repair welds and welds made in close proximity are frequently found in girth welds of critical structures such as tubular trusses, wind turbine towers, pipelines, and pressure vessels, many of which commonly utilize S355 steel. Despite their widespread use, current fatigue design standards offer limited guidance on the performance of welds in close proximity, particularly when different welding procedures are used. These configurations often introduce elevated stress concentrations due to poor joint alignment, high-low misalignment, and unequal wall thickness transitions, all of which can significantly affect fatigue life. To investigate the fatigue performance of welds made in proximity, test specimens were prepared by placing two girth welds in close proximity at distances of 5, 10, and 15 mm, using two distinct welding procedures. A total of 35 small-scale tubular specimens made from S355 steel were fatigue tested under cyclic tensile loading. The mean tensile stress level applied in testing was determined based on measured residual stresses in the parent pipe, obtained using X-ray Diffraction (XRD) prior to specimen extraction, ensuring realistic representation of in-service conditions. Digital Image Correlation (DIC) was employed during testing to capture strain distributions and identify local stress concentration factors. Results indicate that the fatigue limit lies between 150 MPa and 100 MPa, and combined results fell within the design limits of DNV-RP-C203 curve F. Fatigue performance results are presented as S-N curves and stress factors specific to one-sided girth welds in close proximity. This research provides essential technical evidence to support the establishment of design classifications for proximity welds in engineering standards and offers practical guidance for improving the structural integrity and service life of repair welded components in girth-welded structures.
Englund et al. (Fri,) studied this question.