Abstract: The downstream area of seawater pipeline welds is a hot spot for corrosion. In order to explore the influence of weld reinforcements on the corrosion behavior of B30 pipes in the downstream area, the in-situ electrochemical testing device and the home-made circulating seawater-scouring device were used in four scouring-test nodes at 3 d, 7 d, 15 d, 30 d. The impedance spectra were tested with three simulated weld reinforcements (0 mm; 0.5 mm; 1.5 mm) in the adjacent heat-affected zone (HAZ) and 30-mm-downstream base-metal zone (BMZ). The corrosion morphology of the sample surface was observed by the scanning electron microscope (SEM), and the finite-element-simulation flow-model was established by using COMSOL software. The influence of weld reinforcements on the flow state of the medium was discussed. Results show that the impedance values in the HAZ and BMZ were smaller than those of the no-welding in the case of welding. The weld structure would accelerate the corrosion in the downstream zone. The larger the reinforcement, the greater the corrosion tendency. The corrosion rate in the HAZ was larger than that in the BMZ. The flow model showed that an eddy current appeared in the HAZ and accelerated the corrosion there.