Multi-walled tubular member and method of forming

Abstract From the Canadian patent

A multi-walled composite tube member is formed from two superimposed pipes having a gap therebetween. The inner pipe is forcibly expanded in excess of the gap to deform and expand the outer pipe. The expander including a mandrel is forced through the aligned pipes while maintaining the longitudinal alignment. The diameter of the mandrel corresponding to the final desired diameter to finally size the composite pipe section and establish a true round inner passage. An induction heating coil operating at a low frequency operating in the range of low hundreds hertz in contrast to a conventional high frequency unit operating at thousands of hertz is coupled to and moved relative to the expanded …