Heat and corrosion resistant steel pipe having multi-layered coating

Abstract

A heat and corrosion resistant steel pipe having multi-layered coating comprising a steel pipe, a Zn-Ni alloy plating layer deposited to the outer surface of the steel pipe and a polyvinyl fluoride layer formed on the Zn-Ni alloy plating layer with an epoxy resin being intervened therebetween as an intermediate layer. A metal plating layer comprising Zn-Ni plating layer and Ni-plating layer may be used instead of the Zn-Ni plating layer. A chromate layer may be formed on the metal plating layer.

Description

[0001] 1. Field of the Invention[0002] The present invention concerns a pipe of relatively small outer diameter such as less than about 20 mm disposed as a fluid transportation pathway to automobiles or like outer various machineries and, more in particular, it relates to a heat and corrosion resistant steel pipe having multi-layered coating with a protection layer capable of withstanding severe corrosive circumstance.[0003] 2. Description of the Prior Art[0004] As pipeways used for automobiles or other machineries, those products having Zn-plating layer formed to the outer surface of a steel pipe and applied with chromate treatment to the Zn-plating layer have generally been used.[0005] However, working conditions are severe, for example, in braking or fuel pipeways of automobiles and there have been demands for heat resistance under high temperature circumstance such as at the periphery of engines, resistance to external mechanical forces such as scratch resistance and impact shoc...

AI Technical Summary

Problems solved by technology

However, working conditions are severe, for example, in braking or fuel pipeways of automobiles and there have been demands for heat resistance under high temperature circumstance such as at the periphery of engines, resistance to external mechanical forces such as scratch resistance and impact shock resistance in underfloor pipeways that easily suffer from external injuries as well as higher corrosion resistance.

However, in the protection layer formed by the above-mentioned method, it is necessary to increase the Zn-plating layer as greater than 25 um in order to improve the corrosion resistance of the metal plating layer, which brings about a problem that the productivity is remarkably worsened Further, for attaining a tight bonding with the fluoro resin, it is necessary to form the chromate layer by using a chromic acid solution at relatively high concentration containing formic acid, which results in a problem that a lot of chemicals for the treating solution is consumed and the processing cost is increased for the solution wastes containing noxious hexavalent chromium.

If the layer thickness is less than 0.2 um, the coating performance to the iron and steel substrate is poor and no substantial improvement can be obtained for the corrosion resistance.

On the contrary, if the layer thickness exceeds 10 um, peeling, cracking, etc. may possibly be caused upon applying subsequent fabrication such as pressing or bending, to rather deteriorate the corrosion resistance.

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