Method of producing a multiple-wall pipe structure with anticorrosion end protection

A method of producing a multiple-wall pipe structure comprising two pipes tightly fitted one within the other, the inner one of said pipes being of a corrosion-resistant metal and the outer one of said pipes being of a noncorrosion-resistant metal, and a pair of anticorrosion rings of a corrosion-resistant metal integrally attached to opposite ends of said pipes so as to cover at least the end faces of said pipe of the noncorrosion-resistant metal, said method comprising the steps of:

• providing said two pipes in said tightly fitted manner;
• providing said anticorrosion rings;
• bringing each said anticorrosion ring into face-to-face pressing contact against the respective end faces of said pipes, while revolving each said ring about its center axis, thereby friction-welding said ring to said end faces of said pipes;
• and
• preventing inward crimping and separation of the end of said inner pipe away from said outer pipe during said friction-welding by internally chamfering said end faces of said pipes and externally chamfering the end of said anticorrosion ring, such that said chamfered end of said anticorrosion ring fits into said chamfered end faces of said pipes.