Iron-based pipe comprising anticorrosive coating

Abstract

The invention discloses an anticorrosive coating of a nodular cast iron pipe fitting and a nodular cast iron pipe comprising the coating. The anticorrosive coating comprises a ZnAlRE alloy layer and a hole sealing layer, the ZnAlRE alloy layer comprises, by weight, 4.7-60% of Al, 0.02%-5% of RE and the balance Zn, porosity of the coating is 1.0-2.0%, Ecorr is -1.26--1.17V, and Icorr is 1.0-1.1x10<-5>A.cm<2>. The anticorrosive coating and the nodular cast iron pipe have the advantages of environmental protection, low alloy consumption, high corrosion resistance and the like.

Description

technical field [0001] The invention relates to a pipeline and a coating, in particular to an iron-based pipeline, especially to the field of external anti-corrosion of ductile iron pipelines, in particular to an anticorrosion coating for ductile iron pipelines and pipe fittings. Background technique [0002] At present, Zn coating is the most widely used thermal spray coating for buried earth graphite cast iron pipes and pipe fittings. Although Zn coating has good dynamic electrochemical protection performance, on the one hand, the high porosity of Zn coating weakens its On the other hand, in the normal atmospheric environment, the corrosion products of Zn coating are mainly composed of zinc oxide, basic zinc hydroxide and basic carbonate which are difficult to dissolve in water. Such corrosion products have certain self-sealing properties. ability to block the intrusion of corrosive media such as moisture, but in environments with high content of seawater or chloride ions,...

AI Technical Summary

Problems solved by technology

[0002] At present, Zn coating is the most widely used thermal spray coating for buried earth graphite cast iron pipes and pipe fittings. Although Zn coating has good dynamic electrochemical protection performance, on the one hand, the high porosity of Zn coating weakens its On the other hand, in the normal atmospheric environment, the corrosion products of Zn coating are mainly composed of zinc oxide, basic zinc hydroxide and basic carbonate which are difficult to dissolve in water. Such corrosion products have certain self-sealing properties. ability to block the intrusion of corrosive media such as moisture, but in environments with high content of seawater or chloride ions, due to the intrusion of chloride ions, corrosion products such as carbonates that are difficult to dissolve in water on the surface of the Zn coating are quickly loosened and easily Displaced by dissolved chloride salt compounds, greatly weakening the self-healing properties of corrosion products, this reaction has a faster kinetic process

The easy solubility of corrosion products is an important reason for the low corrosion resistance of Zn coatings. At the same time, corrosion products can also cause coating blisters, reduce the adhesion of the coating, and cause the coating to be prone to pitting corrosion and uneven corrosion. Its corrosion life

In addition, environmental pollution is the biggest problem faced by thermal spraying Zn

During the spraying process, the highly atomized metal ions and the ZnO dust generated by oxidation will cause serious pollution to the environment, increasing the number of suspended particles in the air

ZnO dust has strong toxicity, a small amount of inhalation will cause dizziness, nausea, fever, and a large amount of inhalation may even cause death. The layer is changed to spraying ZnAl pseudo-alloy coating or ZnAl alloy coating. Although the corrosion products of ZnAl pseudo-alloy or ZnAl alloy coating have improved the self-sealing effect of the pores in the coating, it is still not complete, resulting in the current ZnAl pseudo-alloy coating. And alloy coatings have poor corrosion resistance

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