The installation of the liner was completed in three phases, each of which included between 15 and 20 miles of pipeline. Before the lining process could begin, the line was first tested for strength and leaks using hydrostatic testing, a process that regulators agreed could replace the more typical approach to measuring wall thickness.
Each phase was further broken down into a series of installations ranging from just 25 to more than 3,000 feet in length. Working in coordination with the owner’s steel and excavation contractor, the HDPE lining contractor arranged for entry and termination sites to be excavated at the beginning and end of each installation.
In each case, the polyethylene pipe was delivered to site and fused together along the right of way. The fusion procedure involved setting two pieces of polyethylene pipe into a fusion machine in a straight line. After each piece was cleaned of any dust, dirt or other material, the two ends were trimmed and carefully aligned to allow for an exact flushness. The ends were then trimmed one more time before being brought together against a heating plate that had been inserted in the machine.
The ends remained under pressure until a visible bead formed completely around the pipe edges. At that point, the pressure is released, the fusion machine is opened and the heater plate is quickly removed. The two ends are then brought together and fused using pressure. After the fused pipe cools naturally, it is removed, the bead is trimmed and examined for any visible flaws.
Using compressed air, a blow down pig with a sizing plate was then inserted the entire length of the steel pipeline section to be lined. This allows the contractor to determine the presence of any abnormalities, such as pipe heavy wall changes, mitered welds, deep weld penetrations, ovallites and dents.
Fused sections of HDPE liner were then passed through a reduction roller box, temporarily reducing the size of the liner. The reduced liner was then pulled through the host pipe until the pull-head emerged at the other end. A wireline truck was used to measure tension and distance, allowing for a tight fit. After the sections were pulled in, time was allowed for the liner to “relax” and revert to near its original size.
When each of the three phases were complete, each segment again underwent hydrostatic testing before it could be returned to service.