Process for manufacturing clad pipe

Abstract

Clad pipe having an inner pipe and an outer pipe metallurgically bonded to each other is manufactured by a process comprising the steps of: (a) preparing an inner pipe and an outer pipe made of different metallic materials, the outer pipe having an inner diameter larger than the outer diameter of the inner pipe; (b) forming an Ni-B layer by electroplating or electroless plating on the surface of one of the pipes facing the other pipe when the two pipes are assembled, the Ni-B layer having a thickness of 2-100 .mu.m and consisting essentially, on a weight basis, of B: 0.5%-7%, Fe: 0%-30%, P: 0%-7%, and a balance of Ni and inevitable impurities; (c) assembling the two pipes by inserting the inner pipe into the outer pipe; (d) subjecting the assembled pipes to cold working for reduction in diameter to such a degree that the outer diameter of the inner pipe is reduced by from 0.5% to 10% to form raw clad pipe in which the inner and outer pipes are in contact; and (e) subjecting the raw clad pipe to heat treatment in the temperature range of 1050.degree.-1250.degree. C. for a time sufficient to metallurgically bond the inner and outer pipes by diffusion bonding.