热网换热站不锈钢换热板点蚀的临界条件

热网二级换热站一般采用板式换热器,在其使役过程中不锈钢换热板一旦出现腐蚀穿孔,不但影响一次水水质,而且干扰换热器稳定运行,甚至影响居民供热,因此阐明换热板发生点蚀的临界条件对于科学设定水质控制标准和防止点蚀发生具有重要意义。为此,通过材料化学分析、XRD、SEM及电化学测试等方法对这一问题进行研究。结果表明:在65℃条件下,304不锈钢点蚀的临界Cl;浓度为125 mg/L,316L不锈钢点蚀的临界Cl;浓度为230 mg/L;不锈钢表面一旦形成垢层,表面会发生局部酸化,此时不锈钢更容易发生点蚀;运行过程中为了防止不锈钢换热板点蚀,不仅要严格控制循环水中Cl;浓度,还应防止换热板表面结垢或附着腐蚀产物。

Critical Conditions for Pitting Corrosion of Stainless Steel Heat Exchange Plate in the Heat Exchange Station of Heat-Supply Network

Plate heat exchangers are always employed in the secondary heat exchange station of heat-supply network. If corrosion perforation took place on stainless steel heat exchange plate during its service, it might not only contaminate the circulating water in primary side, but also disturb the steady running of heat exchangers, or even affecting the heat-supply to resident. Thus, investigating the critical conditions for pitting corrosion of heat exchange plate in this case was instructional for establishing the water quality criterion and preventing pitting corrosion. In order to clarify this issue, material chemical analysis, XRD, SEM and electrochemical tests were conducted. Results indicated that the critical concentrations of Cl;for pitting corrosion of 304 stainless steel and 316 L stainless steel under 65 ℃ were 125 mg/L and 230 mg/L, respectively. Once the scale layer was formed on the stainless steel surface, local acidification would occur on the surface, and the stainless steel was more prone to pitting corrosion at this time. In order to prevent pitting corrosion of stainless steel heat exchange plate during operation, the concentration of chloride ions in circulating water should be controlled strictly, and meanwhile the methods to prevent scale and reduce the amount of corrosion products in the surface of hear exchange plate should be taken as well.