POLYETHYLENE fusion JOINING METHODS AND PROCEDURES
There are three types of heat fusion joints to join a polyethylene pipe: Butt, Saddle and Socket Fusion. Additionally, Electrofusion couplings and saddles are widely used to join polyethylene pipe.
REGULATIONS FOR GAS PIPE JOINING
D.O.T. Regulations require that all persons joining polyethylene gas pipe must be qualified under the operators written procedures. (CFR 49, Part 192, and Part 192.287)
BUTT FUSION/HEAT FUSION AND HDPE PIPE
In the 1960s, polyethylene pipe (HDPE) began to dominate the gas market pipe because of its long lasting and leak-proof qualities. HDPE pipe is corrosion resistant; lightweight; weather, impact and freeze resistant; flexible and tough with a 100-year design life. These qualities make the HDPE pipeline long lasting and inexpensive to install. However the strongest advantage of HDPE pipe compared to other pipe materials is how it is joined together. The butt fusion or heat fusion joint literally makes the HDPE pipeline monolithic, self-restrained and leak-proof. The joint is as strong as the pipe itself.
Today 90% of all new underground gas pipes installed is a HDPE pipe. According to Gas Facts 1999, there is an average of fewer than 10 leaks per year that are not caused by third party damage. This is out of 380,000 miles of gas pipe mains and 28 million service lines in the U.S. Compare this leak record to the water distribution system in the U.S. where a water loss due to leaks of 15 to 25% is considered acceptable. A 25% loss in treated water due to leakage in the pipes would amount to 8.4 billion gallons of water produced but never delivered. Leaks are expensive, not only in the cost of repair but also in lost revenue due to lost product. With the monolithic heat fused pipeline there are no leaks due to joint failure. The only chance for leakage comes from third party damage.
BUTT FUSION/HEAT FUSION AND HDPE PIPE
The butt fused or heat fused joint along with the toughness and flexibility of HDPE pipe explains the popularity of HDPE pipe in trenchless rehabilitation projects. Trenchless rehabilitation using HDPE pipe can be divided in the following categories.
- Sliplining of existing pipe using butt-fused joints consists of digging an entry point and exposing the existing pipeline. The crown is then broken out of the pipeline and the pre-fused HDPE pipe with a pulling head attached is pulled into the existing pipeline from a manhole or another entry point. The butt-fused joints make this possible since they are strong enough to withstand the tensile pull the HDPE pipeline is subjected to.
- If the existing pipeline is undersized and the increased flow due to the improved flow factors of HDPE pipe (C=155) does not provide sufficient flow to meet current or future flow requirements, the project may require pipe-bursting methods of rehabilitation. In this procedure a bursting head--either pneumatic, passive with a splitting head attached to rods, or a pulling head with a hydraulic expander is attached to the HDPE pre-fused pipeline. The strong and flexible HDPE pipeline is then pulled through the existing pipeline, which has been expanded size on size or even expanded to a larger size to increase capacity in undersized pipeline. This is possible because of the strong monolithic HDPE pipe with its butt-fused joints, which are as strong or stronger than the original pipeline.
- Everywhere it is feasible, cities are using HDD trenchless methods of installing new or replacement water mains. HDD is performed by drilling a hole down until the correct depth is reached and then horizontally for as long as the pipe needs to travel. Strong, flexible HDPE pipe with its leak-proof butt fused joints is then pulled back through the directional-drilled hole. Not only is the HDD procedure of installing long lasting HDPE pipe competitive to replacement pipe installation methods, it is the least intrusive. HDD techniques provide little disturbance to expensive landscapes, streets and sidewalks eliminating much of the expense of replacing asphalt, concrete and landscaping. HDD in most cases is made possible because of the strong butt fused joints offered BY HDPE pipe.
Heat fusion joints provide leak-free pipelines eliminating the single largest leak point in other pipe materials.