The background of the invention is set forth in two parts: the field of the invention and the description of related art.
1. Field of the Invention
This invention relates to in situ rehabilitation of pipelines. In particular, it relates to installing a thermoplastic liner in existing pipelines.
2. Description of Related Art
The invention disclosed herein provides improvements to the inventions disclosed in U.S. Pat. No. 5,104,595 by Hunter, Apr. 14, 1992, entitled "Process and Apparatus for In Situ Rehabilitation of Pipelines." The disclosure of that patent is incorporated by reference wherein as if fully set forth.
A limitation of prior art systems is the presence of weld lines in the extruded liner that reduce its melt strength. Another limitation is excessive and uneven shrinkage of the installed liner.
Other background material is provided in a report by Yellowstone Environmental Science, Inc., of 320 S. Willson Ave., Bozeman, Mont. 59715, entitled System for In Situ Rehabilitation of Pipelines Phase II Final Report, Volumes I and II, October 1994. That material is incorporated by reference herein as if fully set forth.