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HDPE FUSION PROCEDURES <br />' HDPE is a thermoplastic material and, as such, pipe joints can be made by <br />welding, or fusing, the pipe ends together. Fusing the pipe ends together is <br />accomplished by facing the pipe ends to insure good contact, heating the pipe ends, <br />and forcing them together. The result of this process is an essentially continuous <br />' pipe wall, where the "welds" become an integral part of the pipe, the same as any <br />other section of wall. <br />In order to insure that fusion joints are made correctly, . he Plastic Pipe <br />Institute (PPI) has developed specific procedures for fusing HDPE pjpe.:,::These, <br />procedures include rules for cleaning and facing the ends of the pipe to be joined, <br />the temperature range to which the..ends of the pipe are heated, the specific <br />pressure to be used for pressing the pipe ends together, and minimum time period to <br />hold the pressure on the newly fused joint. The correct temperature of the heating <br />unit is between 400 and 450 degrees Fahrenheit. The heating time is.determined <br />by the size of the initial "bead" that forms against the heater unit, and is determined <br />in the field. The fusion pressure is calculated based on the pipe diameter and wall <br />thickness. The "cool-down" time, the time during which the fusion pressure is held, <br />is also based on the pipe diameter. Assuming all of the above procedures are <br />followed, a good fusion joint should result. <br />In order to verify that the correct procedures were being used, the fusion <br />machine operator was required to make a test joint at the beginning of every day, <br />with the same machine settings to be used on that day. These sample joints were <br />made with the pipe material used that day, cut from the actual pipe. These test <br />joints were cut into strips that were tested by sharply bending the ends of the strip. <br />If no problems such a splits or cracks at the weld were found, the machine settings <br />were determined to be acceptable. All of the test strips produced for this project <br />were determined to be well made, and no machine settings had to be changed as <br />the result of the testing performed. <br />3 <br />