Abstract: A plastic-lined metallic pipe including an outer metallic pipe which supports an inner plastic sleeve with mechanical engagement between the plastic sleeve and the metallic pipe throughout the circumference of the sleeve. The metallic pipe has a longitudinal weld and the plastic sleeve is melt-bonded to the metallic pipe along the weld only.

Abstract: Apparatus for continuously manufacturing plastic-lined metallic pipe. The apparatus 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 move 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 apparatus 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.

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.

Abstract: A conduit coupling assembly for connecting the end portions of a pair of lengths of conduit in coaxial relationship. The end portions of the lengths have external threads of the same size. The coupling assembly includes an annular outer coupling member and an annular inner coupling member for reception by the outer coupling member. The outer coupling member has a first end including an internal screw thread sized for threading onto the end portion of one of the conduits. This outer member also includes a second end including an outer wall defining a cavity with the outer wall having at least one threaded aperture therethrough opening onto the cavity. The inner coupling member includes a first end and an internal screw thread sized for threading onto the end portion of the other of the conduits.

Abstract: A method for making endless lengths of nylon coated metal tubing which coating has high mechanical strength characteristics and a low gloss surface finish. The method includes passing the formed tubing through a first powder coating region and applying a layer of nylon generally uniformly surrounding the circumference of the tubing. This first nylon powder coating is heated sufficiently to cause the nylon coating to achieve complete melt-flow into a continuous first nylon coating region which would have a relatively high gloss. The coated tubing is next passed through a second powder coating region with the surface temperature of the first coating still above the melting temperature of the nylon. At this second coating region a second powder coating of the same type of nylon is applied. The second coating is cooled below the melting point of the nylon before the second coating completely melts leaving the outer surface with a very low gloss surface finish.