Large-scale I-section beams were welded from A710 (HSLA-80) steel plates. There were plain welded beams, similar beams with two attachment details fillet welded to the tension flange, and similar beams with transverse groove welds. The welding procedures used produced a wide range of welding discontinuities, particularly at groove welds which intersected the longitudinal fillet welds without a cope hole. The 162 beams were fatigue tested in four-point bending in a test matrix which included various stress ranges and minimum stress levels. The discontinuities at the origin of each fatigue crack were identified. These initiating discontinuities included microscopic weld toe discontinuities, porosity, inclusions, lack of penetration and hydrogen cracks. Fracture mechanics fatigue crack growth models were used to calculate the fatigue lives based on the initial discontinuity size. Various methods of idealizing the discontinuities as initial cracks were examined.