The present invention provides a corrosion- and chipping-resistant resin coating structure for stainless steel pipe with a small diameter and thin wall.

The coating structure comprises a stainless steel pipe and a polyolefin or polyamide layer formed on the outer surface thereof. In a preferred embodiment, the coating structure further comprises adhesive layer, a fluoroplastic layer, and a polyamide adhesive layer. The coating structure exhibits good resistance to corrosion with mud and chipping by splashed pebbles.

Metal pipes for the fuel and brake systems are mounted under the automobile floor and are subject to corrosion and chipping by pebbles splashed by tires. Common practice for their protection has been resin coating formed in the following way. For example, a steel pipe (with an optional surface copper layer) is coated with a zinc plating layer and chromate film and then covered with a heat-shrinkable tube of polyvinyl chloride resin or polyolefin resin. Alternatively, the zinc plating layer and chromate film are covered with an intermediate layer of fluoroplastic and an adhesive layer of polyamide resin (particularly nylon 12) on which is slipped a heat-shrinkable tube of polyvinyl chloride resin, polyolefin resin, or fluoroplastic, or on which a gelled lining film is formed from polyvinyl chloride resin. (See Japanese Patent Application Nos. 212255/1988 and 26391/1990.)

A disadvantage of the conventional coating structure mentioned above is that it requires that the ends of the metal pipe be stripped off the heat-shrinkable plastic tube so as to facilitate the insertion of flared fitting and hence the exposed ends are subject to corrosion and chipping. In the case where lining film is formed instead of covering with a heat-shrinkable film, it is necessary to preliminarily mask the ends of the metal pipe.

It is an object of the present invention to provide a corrosion- and chipping-resistant resin coating structure for stainless steel pipes with a small diameter and thin wall. The resin-coating structure is suitable for fluid piping, especially piping for the automotive fuel and braking system which is mounted under the automobile floor and is subject to corrosion with mud and chipping by splashed pebbles.

In order to eliminate the above-mentioned disadvantage and to achieve the above-mentioned object, the present inventors carried out a series of researches which led to the finding that the object is achieved by forming a resin layer directly on a stainless steel pipe, thereby ensuring adhesiveness.

The first aspect of the present invention resides in a corrosion- and chipping-resistant resin coating structure for stainless steel pipes, said structure comprising a polyolefin or polyamide resin layer formed on the outer surface of a stainless steel pipe.

The second aspect of the present invention resides in a corrosion- and chipping-resistant resin coating structure for stainless steel pipes, said structure comprising an underlying adhesive layer of epoxy resin and a polyolefin or polyamide resin layer formed on top of the other on the outer surface of a stainless steel pipe.

The third aspect of the present invention resides in a corrosion- and chipping-resistant resin coating structure for stainless steel pipes, said structure comprising an underlying adhesive layer of polyamide resin and a polyolefin or polyamide resin layer formed on top of the other on the outer surface of a stainless steel pipe.

The fourth aspect of the present invention resides in a corrosion- and chipping-resistant resin coating structure for stainless steel pipes, said structure comprising an underlying adhesive layer of epoxy resin, an intermediate layer of fluoroplastic, and a polyolefin or polyamide resin layer formed consecutively on the outer surface of a stainless steel pipe.

The fifth aspect of the present invention resides in a corrosion- and chipping-resistant resin coating structure for stainless steel pipes, said structure comprising an underlying adhesive layer of epoxy resin, an intermediate layer of fluoroplastic, an adhesive layer of polyamide resin, and a polyolefin or polyamide resin layer formed consecutively on the outer surface of a stainless steel pipe.

According to the coating structure of the present inventions a stainless steel pipe is coated directly or indirectly with a polyamide or polyolefin resin layer which firmly adheres to the pipe and protects the pipe from splashed pebbles. In another embodiment, an intermediate layer of flexible fluoroplastic is interposed between the pipe and the resin coating layer so as to improve adhesion between the pipe and the coating layer and to improve protection from splashed pebbles by increased shock absorption.