US Patent 7653999 Co-extruded generating bank swaged tubing

A method is provided for successfully rolling co-extruded tubing into drums of a boiler bank. First, a co-extruded tube is provided, containing a carbon steel base tubing with an outer layer of high alloy tubing. Next, the outer layer of high alloy tubing is removed by machining in the area of the co-extruded tubing that is to be rolled into the drum. Then, the co-extruded tubing is swaged using multiple swaging steps and annealing treatments. The co-extruded tubing is swaged to the required diameter and wall thickness. Finally, co-extruded tubing is inserted, rolled, and sealed into the drums.