Abstract:

In recent years, many thermal power units in China that equipped with SCAL type indirect cooling systems have commonly encountered corrosion and leakage problems with aluminum radiators. This study conducted field research and systematic analysis on more than ten units of the same type to reveal the corrosion mechanism of pure aluminum materials. Cl^- ions destroy the passivation film protective layer on the surface of pure aluminum and undergo a secondary reaction with aluminum corrosion product Al(OH)₃ to generate OH^-, resulting in an abnormal increase in the pH of the indirect cooling circulating water. The alkaline environment accelerates the dissolution process of the passivation film, thereby further exacerbating the corrosion of the aluminum substrate. In addition, SO₄ ^2- accelerate the corrosion of carbon steel and generate corrosion product of Fe₃O₄. After the passivation film on the surface of pure aluminum dissolves extensively in an alkaline environment,Fe₃O₄ will have a significant erosion corrosion effect on the exposed aluminum substrate under the high-speed fluid. Based on the above results, this article proposes three targeted corrosion control measures: 1) adding bypass purification devices to improve the quality of circulating water; 2) Installing protective sleeves at the aluminum radiator nozzle to reduce erosion and corrosion; 3) Scientifically adding corrosion inhibitors to enhance the anti-corrosion performance of the system.

Key words: SCAL type indirect cooling system, indirect cooling circulating water, carbon steel, pure aluminum, corrosion

摘要：

近年来，我国多台采用表面式换热器铝制散热器（SCAL）型间冷系统的火电机组出现铝制散热器腐蚀泄漏问题。通过对十余台同类型机组的实地调研与系统分析，揭示了纯铝材料的腐蚀机理：Cl^-会破坏纯铝表面的钝化膜保护层，并与铝腐蚀产物Al（OH）₃发生次生反应生成OH^-，导致间冷循环水pH异常升高，而这种碱性环境又会加速钝化膜的溶解进程，从而进一步加剧铝基体的腐蚀。同时，SO₄ ^2-会加速碳钢的腐蚀并生成腐蚀产物Fe₃O₄，纯铝表面的钝化膜在碱性环境中大面积溶解后，Fe₃O₄在高速流体作用下会对裸露的铝基体产生显著的冲刷腐蚀作用。基于上述研究结果，提出了3种针对性的腐蚀控制措施：1）增设旁路净化装置以改善循环水水质；2）在铝制散热器管口加装防护套管以减轻冲刷腐蚀；3）投加缓蚀剂以增强系统防腐性能。

关键词: SCAL型间冷系统, 间冷循环水, 碳钢, 纯铝, 腐蚀

CLC Number: 

• TG174