PTA装置脱水塔T403入口管线腐蚀分析

Analysis of Corrosion of Inlet Line of Dehydration Tower T403 in PTA Unit

介绍了PTA装置溶剂回收系统脱水塔T403入口管线焊缝及基材的腐蚀情况,通过宏观和低倍观察,发现入口管线焊缝区发生冲刷腐蚀及化学腐蚀;通过金相与硬度测试及材质成分分析,发现入口管基材与焊缝的成分和组织的差异;通过扫描电镜分析和电化学试验等方法分析其各自电化学性能,发现基材的耐蚀性明显地高于焊缝处,从而使得焊缝区容易发生优先腐蚀;加上流体的冲刷腐蚀,使焊缝处逐渐凹下,从而导致经过该处的流体产生湍流,最终加剧该焊缝处的冲刷腐蚀,直到焊缝穿孔。为防止焊缝的优先冲刷腐蚀,应选择耐蚀性略高于至少同于基材耐蚀性的焊缝金属,并对焊后的焊缝表面进行有效的处理,以减少流体对其的重点冲刷。实践证明,PTA装置中,在水与醋酸的环境下,钛材是最好的选择。

The corrosion in welds and base material of inlet line of dehydration tower in solvent recovery system of PTA unit was introduced. The macro inspection and low - power examination found impingement erosion and chemical corrosion at welds of inlet line. The metallography and hardness testing and metallurgy analysis found the differences in composition and structure between base material of inlet line and welds. The analysis of chemical properties by scanning electron microscope （ SEM ） and electro - chemical testing demonstrated that the corrosion resistance of base material was obviously higher than that of welds. Therefore, the welds were subject to corrosion. Under the effect of impingement of fluid, the welds were gradually becoming concave which resulted in turbulent flow of fluid and finally led to erosion corrosion and welds failure. To prevent erosion corrosion of welds, the welding metal whose corrosion resistance is equal to or greater than that of base material shall be selected, and the weld surface should be effectively treated to minimize the impingement of fluid. The practice has showed that Ti material is a good selection for acetic acid and water environment in PTA unit.