Method of producing multiple-wall, composite tubular structures

A method of producing multiple-wall composite tubes, said method comprising:

• inserting an inner tube into an outer tube;
• applying pressure to the interior of said inner tube and thereby causing said inner tube to expand plastically into tight contact with said outer tube;
• with said inner and outer tubes in such state of tight contact, and while said pressure is maintained applying heat from the outside to said outer tube only without applying substantially any heat to said inner tube and thereby creating a temperature difference between said inner and outer tubes and causing said outer tube to expand in diameter, said applying heat comprising establishing, by high-frequency induction heating means, a locally heated zone of said outer tube substantially around the circumference thereof, and causing said heated zone to travel from one end to the other end of said outer tube, thereby causing said outer tube to successively expand locally in the traveling heated zone;
• and
• then removing said pressure from the interior of said inner tube, and permitting said tubes thereafter to obtain ambient temperature and obtain a fit of high degree of interference therebetween.