HDPE pipe is the most widely used pipe all over the world, because of its easy and multiple uses. Another excellent feature of the HDPE pipe is, it can be extended to as long distance as you need. And that leads us to HDPE pipe joining. There are many methods for joining them, and each comes with advantage and disadvantage. So, today let looks at the three different methods of joining an HDPE pipe.
Butt Welding
Also, known as butt fusion, butt welding procedure is a thermofusion process that involves the simultaneous heating of ends of two components which will be joined until a melting state is reached on each contact surface, thereby producing a permanent, economic and flow-efficient connection.
After reaching a melting state, both surfaces are brought together under controlled pressure for a specified cooling time, and homogenous fusion is formed upon cooling. Now, we get the joint that we resistant to end thrust and performs well under pressure as well. For butt welding, we need an electrically heated plate for raising the temperature of the pipe ends to required fusion temperature.
The pre-welding procedure for butt welding is outlined below.
-You need to create a clean and stable environment at the point of fusion.
-Make sure the equipment are clean and in working condition.
-Do not take any chances and try this out by yourself. Hire skilled personnel and carry out the work.
-Go through the preliminary welding procedures and weld accordingly.
-Inspect the welding process correctly and make changes as well until you have achieved a pass status.
-While carrying out the procedure, do not forget to record all the parameters as well.
-Ensure the use of check sheets for the accurate tracking of all steps and parameters.
Now begins the actual welding process. Go through the points properly and do not miss the steps.
-Place the pipes in pipe clamps with ends against the trimming tool and pipe marking aligned.
-Now, you need to align and level components using support rollers.
-Make sure to tighten the pipe clamps for good grip and re-round the pipes.
-Use trimming tool to ensure continuous shaving are cut from each surface.
-Make sure there is no visible gap between trimmed faces.
-Now place the heater plate in the machine and close the clamps, so the surface to be joined is touching the plate.
-Apply the pressure using a hydraulic system.
-Maintain the pressure until pipes begin to melt, and a uniform bead of 2-3mm is formed on each end.
-Do not let the pipes slip in the clamps. Pipe ends must maintain contact with heater plates.
-After the heat soak is completed, remove the heater plate and ensure the plate does not touch the melted surface.
-Now close the clamps immediately and bring the melted surface together at previous pressure.
-Hold under pressure for appropriate cooling time.
Electrofusion
Electrofusion is another way of joining HDPE pipes, which is also considered as the highly developed, cost-effective and safe method. The process uses the heat generated from electricity to melt pipe wall and pipe surface which creates a completely homogenous joint that is stronger than the pipe itself. This method is also very effective when the access is difficult in situations like trenches or around other pipes. However, electrofusion is for trained welder, so better not try this method by yourself.
Let us look at the pre-welding procedure of electrofusion.
-You need to create an environment conducive to repeatability and reproducibility, so a clean and stable environment at the point of fusion is needed.
-Make sure you have trained personnel, and all the equipment is on the side.
-Ensure that the welding is carried out as per the preliminary welding procedure.
-Perform visual inspection and mechanical tests on the welded section.
-Do record at the parameters and keep tracks of every step.
Getting towards the actual welding process, following are the steps.
-The pipe should be cut at 90 degrees to the pipe axis.
-Mark fusion zone on the pipe and scrape to remove the oxide layer.
-Clean the scraped area of pipe and fitting while avoiding any touch in the fusion zone.
-Now, you have to mark the insertion depth on both pipes ends to be joined.
-You have to insert the pipe ends into electrofusion fitting and for larger dimensions assembly can be assisted by tapping around the face with a plastic hammer.
-Using the preheating phase start the fusion process.
-Wait for the appropriate cooling time and check the fusion.
-Do not forget to mark the fusion parameters on the pipe.
Flanged connections
Flanged connections are used to connect PE pressure pipelines to valves, pumping stations and pipeline of other pipe materials. For flanged joint, you will need the following components.
-Stub-ends or flanged adaptors
-Back-up flanges
-Gaskets which are pressure and chemical appropriate.
-Bolts and washers
The general procedure for flanged connections are:
-Center the flanges and gasket in a way that supports one or both halves of joint if necessary.
-Make sure the end surface of stub-ends must be close to each other before the bolts are tightened to avoid elongation of the pipe during joint assembly.
-Tighten the bolts starting with finger tightening and consequently using a torque wrench.
Mechanical Compression Coupling
Mechanical Compression coupling is a popular temporary joint for HDPE pipes. As they require no soldering, and very quick and easy to use, this method requires almost no skill. Also, there is no need for special tools too. The method is useful for installation that may require occasional disassembly or partial removal for maintenance.