Method and apparatus for manufacturing plastic-lined pipe

Abstract

Method for continuously manufacturing plastic-lined metallic pipe. The method includes an extruder having an output providing a plastic sleeve and further includes a continuous roll-forming tubing mill production line. This production line includes a series of forming rolls which progressively deform a substantially flat steel strip to a generally tubular configuration as the strip moves along a straight-line longitudinal path. The production line further includes an electrical resistance or high frequency welder which continuously welds the lateral edges of the moving strip to complete the pipe. The method also includes a feed for the plastic sleeve into the incipient metal pipe upstream of the welder. The plastic sleeve has an outside diameter slightly smaller than the inside diameter of the metallic pipe in its as-formed condition. Furthermore, the plastic sleeve maintains a generally tubular configuration from the time it enters the pipe until the manufacture of the plastic-lined pipe is completed. The exterior surface of the metal pipe can be galvanized in the production line, or raw steel pipe can be lined and the exterior surface later painted. The production line also includes a sizing station for reducing the inside diameter of the metallic pipe to substantially the outside diameter of the plastic sleeve.