Influence of weld reinforcements on corrosion behavior of Cu-Ni alloy pipe
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摘要: 海水管道焊缝下游区是发生腐蚀的热点区域. 为探究B30管道焊缝余高对与其下游区腐蚀行为的影响，利用原位电化学测试装置和自制循环海水冲刷装置，在3 天、7 天、15 天、30 天4个冲刷节点进行试验. 测试了3种模拟焊缝余高(0 mm；0.5 mm；1.5 mm)在紧邻热影响区和下游30 mm处母材区的电化学阻抗谱，用扫描电镜观察了试样表面的腐蚀形貌，结合COMSOL软件建立了有限元仿真流态模型，探讨了余高对介质流态的影响. 结果表明, 在有焊缝情况下，热影响区和母材区阻抗值均小于无焊缝结构，焊缝结构会加速下游区的腐蚀，且余高越大，腐蚀倾向也越大；热影响区腐蚀速率均大于母材区；流态模型显示出在热影响区位置出现了涡流，涡流加速了热影响区的腐蚀.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.
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图 2 在不同时间、模拟焊缝余高为1.5 mm时的热影响区的SEM形貌
Figure 2. Surface SEM morphology of HAZ with the simulated 1.5 mm weld reinforcement. (a) 3 day; (b) 7 day; (c) 15 day; (d) 30 day
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图 3 在不同时间、模拟焊缝余高为1.5 mm时的母材区
Figure 3. Surface SEM morphology of BM with the simulated 1.5 mm the weld reinforcement at different time. (a) 3 day; (b) 7 day; (c) 15 day; (d) 30 day
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图 4 模拟焊缝余高为1.5 mm时的热影响区和母材区的电化学阻抗谱
Figure 4. Electrochemical impedance spectroscopy of HAZ with the simulated 1.5 mm weld reinforcement and the BMZ. (a) Nyqusit diagram of HAZ; (b) Bode diagram of HAZ; (c) Nyqusit diagram of BMZ; (d) Bode diagram of BMZ
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图 5 模拟焊缝余高为0.5 mm时的热影响区和母材区的电化学阻抗谱
Figure 5. Electrochemical impedance spectroscopy of HAZ with the simulated 0.5 mm weld reinforcement and the BMZ. (a) Nyqusit diagram of HAZ; (b) Bode diagram of HAZ; (c) Nyqusit diagram of BMZ; (d) Bode diagram of BMZ
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图 6 无模拟焊缝的热影响区和母材区的电化学阻抗谱
Figure 6. Electrochemical impedance spectroscopy of HAZ without a simulated weld reinforcement and BMZ. (a) Nyqusit diagram of HAZ; (b) Bode diagram of HAZ; (c) Nyqusit diagram of BMZ; (d) Bode diagram of BMZ
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图 7 在第30天时、不同余高的模拟焊缝的热影响区和母材区的阻抗值
Figure 7. Electrochemical impedance spectroscopy of HAZ with different simulated weld reinforcements and BMZ at 30 day
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图 9 余高为0.5 mm的流场仿真图
Figure 9. Flow field simulation diagram with the 0.5 mm weld reinforcement
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图 10 余高为1.5 mm的流场仿真图
Figure 10. Flow field simulation diagram with the 1.5 mm weld reinforcement
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