130℃热网循环水中316L和317L不锈钢换热板点蚀临界条件实验研究

Experimental study on critical conditions for pitting corrosion of 316L and 317L heat exchange plate used in 130℃circulating water in heating network

随着城市集中供热规模不断扩大,热网循环水温度已经从95℃升至130℃,温度升高后不锈钢换热板的点蚀穿孔现象加重,因此研究130℃热网循环水中不锈钢点蚀的临界条件对于建立热网循环水水质控制标准具有重要的指导意义。本文根据宁夏某供热公司热网循环水水质特点,在实验室通过电化学测试及静态模拟实验研究了316L和317L 2种不锈钢材质的点蚀临界条件。结果表明:该热网二次侧循环水具有pH值8.3~8.4,且SO42–与Cl^-质量浓度之比≥1的水质特点;在该水质特点环境中130℃时316L不锈钢发生点蚀的临界Cl^-质量浓度在15.44~21.45 mg/L之间,使用316L不锈钢换热板的热网系统应控制循环水中Cl^-质量浓度小于15 mg/L;317L不锈钢发生点蚀的临界Cl^-质量浓度在42.90~53.62 mg/L之间,使用317L不锈钢换热板的热网系统应控制循环水中Cl^-质量浓度小于40 mg/L。

With the expanding of central heating scale in city,the temperature of circulating water in primary heating network has raised from 95℃to 130℃.With the temperature increasing,pitting corrosion becomes more serious on stainless steel heat exchange plate.Thus,investigating the critical conditions for pitting corrosion of stainless steel in this case is instructional for establishing the water quality criterion of circulating water.In this work,the characters of water quality of circulating water in heating network from a heating supply company in Ningxia was analyzed firstly.Then,electrochemical tests and simulated experiments were conducted to clarify the critical conditions for pitting corrosion of 316L and 317L.The results indicates that,the pH value of the water is 8.3~8.4 and the ratio of mass concentration of SO42–to Cl^-is greater than or equal to 1.In the environment at 130℃with this characters,the critical mass concentration of Cl^-for pitting corrosion of 316L is 15.44~21.45 mg/L,and the critical concentration of Cl^-for pitting corrosion of 317L is 42.90~53.62 mg/L.Therefore,the mass concentration of Cl^-needs to be controlled below 15 mg/L in the heating network with 316L heat exchange plant and below 40 mg/L in the heating network with 317L heat exchange plant.