Method and apparatus for manufacturing plastic-lined pipe

A method of continuously manufacturing plastic-lined metallic pipe using an extruder for making a tubular plastic sleeve having a predetermined outside diameter and a continuous roll mill production line which functions to progressively deform a metal strip from a generally flat configuration to a generally tubular configuration as the strip moves along a straight-line longitudinal path, and to continuously weld adjacent lateral edges of the moving strip to complete the pipe, said method comprising the following steps:

• (A) feeding said tubular plastic sleeve into the incipient metal pipe upstream of the location of welding, said plastic sleeve having an outside diameter slightly smaller than the inside diameter of the metal pipe;
• (B) maintaining said plastic sleeve in its generally tubular configuration and with substantially said predetermined outside diameter from the time said sleeve enters said incipient metal pipe until said method is completed;
• (C) continuously welding together said adjacent lateral edges downstream of the location of entry of said sleeve into said incipient metal pipe;
• and
• (D) sizing said metallic pipe downstream of the location of welding to reduce the inside diameter of said metal pipe to substantially the outside diameter of said plastic sleeve to mechanically lock together said pipe and said sleeve thereby forming said plastic-lined metallic pipe.