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首页> 外文会议>Associazione Italiana Di Metallurgia;Dechema;Annual event of the European Federation of Corrosion on European Corrosion Congress;uropean Federation of Corrosion >Corrosion failure analysis of galvanized steel pipes in a closed water cooling system
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Corrosion failure analysis of galvanized steel pipes in a closed water cooling system

机译：闭式水冷系统中镀锌钢管的腐蚀失效分析

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The present study is focused on the failure analysis of water cooling systems serving a PET (polyethylene terephthalate) preform moulding plant. PET preforms have application in the field of drinking water, fresh milk and soft drink bottles.Cooling systems under examination operate at 6℃ and 20℃.When the plant was set up, the cooling circuits were made from carbon steel. Mixture of water and ethylene glycol was used as coolant. Ethylene glycol was added with corrosion inhibitor to prevent corrosion.The lack of proper control of plant management led to dramatic corrosion in the form of high dissolution rate of the base metal. This involved the risk of severe loss of functionality of the plant itself.The following critical factors were identified:1. In 2009, carbon steel pipes were completely replaced with galvanized steel ones. Nevertheless, the corrosion inhibitor was added again to the coolant.2. The plant was equipped with a water softener that didn’t operate properly, thus promoting the release of chlorides.3. Ethylene glycol was not replaced and its decomposition to organic acids brought to an increase of acidity.All these factors contributed to corrosion initiation and propagation.Chemical analysis were carried on water from both well and closed cooling circuits.Analysis of water from the circuits revealed a very high amount of metals in solution (mainly Zn and Fe) and in the sediment. High chloride content was also determined.The water pH was slightly acidic as a consequence of ethylene glycol decomposition e iron hydrolysis reactions.It is possible to say that the failure of the pipes before their expected lifetime was induced by acidic corrosion. Zinc dissolution rapidly exposed the steel surface. Moreover, the deterioration of the pipes was enhanced by the mechanical wear resulting from a substantial amount of suspended solids in the flowing water.
机译：本研究的重点是为PET（聚对苯二甲酸乙二酯）瓶坯成型厂提供水冷却系统的故障分析。 PET瓶坯已应用于饮用水，新鲜牛奶和软饮料瓶领域。正在检查的冷却系统在6℃和20℃下运行。工厂建成后，冷却回路由碳钢制成。水和乙二醇的混合物用作冷却剂。乙二醇中加入了缓蚀剂以防止腐蚀。对工厂管理的不当控制导致以贱金属的高溶解度形式出现剧烈腐蚀。这涉及到工厂本身功能严重丧失的风险。确定了以下关键因素：1。 2009年，碳钢管被镀锌钢管完全取代。但是，还是在冷却液中添加了缓蚀剂。2。该工厂配备了运行不正常的软水器，从而促进了氯化物的释放。3。乙二醇没有被取代，其分解为有机酸增加了酸度。所有这些因素都促进了腐蚀的发生和蔓延。对井和闭式冷却回路中的水进行了化学分析。溶液和沉积物中的金属含量很高（主要是锌和铁）。还测定了高氯化物含量。由于乙二醇的分解和铁的水解反应导致水的pH值呈弱酸性，可以说是在管道的预期寿命之前的失效是由酸性腐蚀引起的。锌的溶解迅速暴露在钢表面。此外，由于流动水中大量悬浮固体导致的机械磨损加剧了管道的劣化。

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