热镀锌钢管表面黑变形成机理研究及解决方案探讨

    Research on Mechanism of Surface Blackening of Hot-galvanized Steel Pipe and Discussion on Relevant Solution

    • 摘要: 研究了镀锌钢管表面黑变的机理及成因;通过中性盐雾试验和高温高湿试验,探讨了钢管表面黑变的解决方案。结果显示,钢管表面黑变成因与表面锌层中铅元素的含量及分布直接相关。铅含量较高区域腐蚀电位较高,铅含量偏低区域腐蚀电位相对较低。当有腐蚀介质存在时,会发生电化学腐蚀,使电位较低区域加快腐蚀,从而导致该区域腐蚀产物富集,氧元素含量增加。腐蚀产物的富集造成了该区域表观色泽变暗,形成暗黑色表面斑纹。选用GDC-008 型单组份钝化液,钝化膜固化温度达到90 ℃以上、固化时间3 min 以上时,可以获得耐腐蚀性能良好的表面钝化膜层,有效解决镀锌钢管表面黑变问题。

       

      Abstract: Studied are the mechanism and contributing factors of surface blackening of the hot-galvanized steel pipe.And relevant solution proposal for the said problem is discussed via the NSS test and the high temperature/high humidity test.As a result it is revealed that the origin of the pipe surface blackening is directly related to the content and distribution of the lead in the surface zinc layer of the pipe,i.e.,in areas with high lead content,the corrosion potential is higher,whereas in areas with low lead content,the corrosion potential is relatively lower.When the corrosive medium is present,electrochemical corrosion will occur so as to,accelerating corrosion in areas with low potential,resulting in enrichment of corrosion products,and increase of oxygen content in the areas.The enrichment of corrosion products cause the apparent color of this area to become dark,and formation of black striped surface markings.When GDC-008-type one-component passivation solution is,and the curing temperature of the passivation film reaches over 90 ℃,and the curing time is over 3 min,a surface passivation film with good corrosion resistance can be obtained,and thus the problem of surface blackening of the galvanized steel pipe can be effectively solved.

       

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