Patent ID: 7735207

Claim:
A process for manufacturing a plastic-lined metallic pipe for conveying liquid or gas, comprising steps of: placing an alloy outer pipe in a mould with a diameter slightly larger than the outer pipe's outer diameter; warming the outer pipe evenly to a first temperature; cooling a plastic inner pipe evenly to a second temperature at which the inner pipe's diameter is at its shortest point; inserting the inner pipe into the outer pipe to constitute an inner sleeve; drawing from both ends of the outer pipe along its axial direction to extend the outer pipe's length at a tensile ratio in a range of 0.1-1% such that the outer pipe's inner diameter is inwardly merged to the inner pipe's outer diameter; and cooling the outer pipe to a storage temperature such that the outer pipe's inner diameter and the inner pipe's outer diameter are melt-bond without an intermediate layer; wherein the second temperature is lower than the storage temperature.