铜管不锈钢管腐蚀性能及铁牺牲阳极保护研究

铜管一直是电厂凝汽器的主要应用管材，但由于其抗冲刷和抵御污染物腐蚀的能力差，特别不耐氨蚀，美国和欧洲大量使用不锈钢管替代铜管作为冷凝管，然而不锈钢管在我国的运用仅处于初步阶段。 常使用锌、铝阳极对铜管进行牺牲阳极保护，然而存在着电位差过大、阳极溶解过快的问题。铁基牺牲阳极与铜电位差适当、来源广泛、价格便宜，在一些工程上有所应用，但是目前针对铁基牺牲阳极的理论研究报道很少。 本文选用紫铜管、304不锈钢管作为实验用管材，首先运用实验室全浸实验、极化曲线和电化学阻抗研究了二者在海水和淡水中的腐蚀性能以及CO2、溶解氧对其腐蚀的影响。结果表明：CO2会加速二者的腐蚀，溶解氧却对它们的腐蚀影响不同，促进铜管的腐蚀却抑制不锈钢管的腐蚀；随浸泡时间的延长，紫铜管由于表面产物膜的生成耐蚀性提高，304不锈钢管的耐蚀性却降低；淡水中，304不锈钢管和紫铜管都具有很好的耐蚀性能。随后，运用失重法和极化曲线对比研究了紫铜管、304不锈钢管的氨蚀性能，运用SEM分析和电化学阻抗研究了紫铜在不同浓度氨溶液中的腐蚀机理。发现，304不锈钢管的耐氨蚀能力远远好于铜管；溶解氧是影响氨蚀的关键因素，其对二者氨蚀的影响也不同；紫铜管在低氨浓度和高氨浓度溶液中腐蚀机理和产物不同，低氨浓度时形成保护性的产物膜（CuO 和Cu(OH)2），高氨浓度时由活化溶解控制，生成可溶的[Cu (NH3)4]2+。 选用工业纯铁、35钢为牺牲阳极材料。恒电流实验结果表明它们具有良好的牺牲阳极性能；通过极化曲线和自腐蚀电位测试分析，认为将二者用于铜管牺牲阳极保护是可行的；实验室阴极保护效果测试表明，工业纯铁和35钢对紫铜管具有良好的保护效果，保护度达90%以上。

Copper tubes are the main applied pipes of condensers at all times. However, because of their weak resistance to erosion and corrosion from pollutants and ammonia, copper tubes are replaced largely by stainless steel tubes in Europe and America. But in our country the application of stainless tubes is only at beginning stage. Zinc and aluminum are usually used as sacrificial anodes to protect copper tubes. But the potential gap between copper and zinc (or aluminum) is too large, so that anodes dissolved too rapidly. Iron-based anodes have a proper potential, a wide source and a low cost, so they have been applied in some projects. However, theoretical studies and reports on iron-based anodes are very few now. In this paper, copper tube and 304-stainless steel tube were chosen as the specimen tubes. Firstly, their corrosion performance and the impacts of CO2 and O2 on it were studied by immersion test. It showed that, CO2 accelerated their corrosion, whereas dissolved oxygen (DO) had different impacts on them, accelerating corrosion of copper but restraining corrosion of 304-stainless steel. As time went, corrosion resistance of copper tubes improved because of the corrosion product scale, but corrosion resistance of 304-stainless steel tubes declined. In freshwater, both of them have very good corrosion resistance. Subsequently, corrosion performance of copper tubes and 304-stainless steel tubes in ammonia solution were studied contrastively by weight-loss method and electrochemical polarization, and then corrosion mechanism of copper tubes in ammonia solution with different concentration was studied by SEM and EIS. It showed that, 304-stainless steel tubes have much better corrosion resistance in ammonia solution. DO was the key factor which affected ammonia corrosion and it also had different impacts on copper and 304-stainless steel. Corrosion mechanism and products of copper tubes were different in ammonia solution with high or low concentration. When less than 2000mg/L, protective corrosion scale (CuO and Cu(OH)2) formed on copper tubes; when more than 2000 mg/L, copper tubes dissolved, and the product was [Cu (NH3)4]2+. Industrial pure iron and 35-steel were chosen as the sacrificial anodes. Results of invariable current experiment showed they had good performance of sacrificial anodes. It was considered feasible to apply them to protect copper tubes after analyzing their polarization curves and free potentials. Cathodic protection in laboratory showed that they had good protective effect on copper tubes, and protective degrees could achieve above 90%.