Join
After the heater tool is removed, quickly inspect the pipe ends. (NOTE: If a concave melt surface is observed, unacceptable pressure during heating has occurred and the joint will be low quality. Do not continue. Allow the component ends to cool completely, and restart at the beginning. Except for a very brief time to seat the components fully against the heater tool, do not apply pressure during heating). If acceptable, immediately bring the molten pipe ends together with sufficient fusion force to form a double rollback bead against the pipe wall. For manual machines, apply enough force so the bead rolls back and touches the pipe OD and hold that pressure for the minimum cool time. A torque wrench may be used to apply the proper force. To calculate the gauge pressure (psig) for hydraulic butt fusion machines, first determine the fusion force (lbs) required by multiplying the interfacial pressure, 60 - 90 psi (usually 75 psi), by the pipe area (sq. in.). The fusion force is then divided by the total effective piston area (sq. in.) of the carriage cylinders to give the theoretical fusion pressure (psi). Internal and external drag must be added to this figure to obtain the actual fusion machine gauge pressure (psig). The hydraulic gauge reading is dependent upon pipe diameter, DR and machine design. Interfacial pressure and gauge reading are not the same value.
Ref. Polyethylene Piping Systems Field Manual for Municipal Water (Irving, TX: The Plastics Pipe Institute, 2010)
Hold
Hold the joint immobile under fusion force until the joint has cooled adequately to develop strength. Allowing proper cooling times under fusion force prior to removal from the clamps of the machine is important in achieving joint integrity. The fusion force should be held between the pipe ends for a minimum of 11 minutes per inch of pipe wall thickness. Remove the pipe from the fusion machine and avoid rough handling for an additional 30 minutes.
Ref. Polyethylene Piping Systems Field Manual for Municipal Water (Irving, TX: The Plastics Pipe Institute, 2010)