P.E.S Technical Instruction

1. General considerations

The quality of PE pipe welding is dependent on:

• Welder skill
• Welding machine
• The use of welding manuals

2. Pre-welding tips

The welding area should be protected from inappropriate atmospheric factors such as moisture or temperatures below +5 ̊C. If one side is warmer than another side due to intense sunlight, non-uniform heat generation on pipe surface should be prevented using an umbrella or tent. Wind and air currents also should be prevented during welding by closing the pipe ends.

PE pipes that are transported as coils have an oval cross section immediately after opening. Accordingly, the welding area should be first turned into a circle using hot air or a mold before welding. The welding area should be free of any dust and oil. So the welding area should be carefully cleaned before welding.

3. Butt fusion

• Instruction- For butt fusion, two pipe ends are pressed to a hot plate. Then pressure is reduced to a minimum value and pipe ends are heated. After removing the hot plate, the pipe surfaces are welded together under pressure (Fig. 1).
• Preparation for welding- Before welding, the temperature of the hot plate should be measured by a digital thermometer. The temperature of those parts of the hot plate in contact with pipe should be controlled. After ensuring the correct temperature of the hot plate, the operator should wait for 10 min to obtain an uniform temperature on the hot plate. Before welding and heating the hot plate, it is recommended to clean the surface of the cold plate by fabric or fluff-free paper.

Any welding machine has its own specifications regarding welding force or pressure as often reported by manufacturers. To obtain the force or pressure required for welding, the welding pressure should be calculated from welding area and added to the machine force read from pressure gage. In other words, the total welding pressure equals the pressure for moving the machine plus the pressure required for welding per unit area. After cutting and flattening the welding area, the fillings should be removed by a brush. Do not touch the welded section. The both welding surfaces should be cleaned before welding by ethanol 99% using a soft paper.

After joining the pipes, the gap between them and level are controlled. The gap between the two pipes should be in accordance with relevant standards (Table 1).

The difference between the areas of two pipes can be up to 10% of the pipe thickness, but not more than 0.5 mm.

• Welding- In butt fusion, the welding area reaches the welding temperature and two pipes are pressed together after removing the hot plate. The welding temperature ranges from 200 to 220 ̊C. The required temperature is obtained from Fig. 2.

4. Fastening

In this case, the two pipes are pressed to the hot plate from both sides uniformly. An edge is formed on both sides of the plate. Fastening is completed when an edge with specifications in the second row of Table 2 is formed.

5. Heating

Upon formation of the welding edge, pressure is reduced to a minimum of 0.02 N/mm² and heating is started. Heat diffuses the welding area to prepare the thermoplastic pipe for welding. Heating duration can be found in the third raw of Table 2.

6. Conversion

Upon completion of heating, the plate should be slowly removed to avoid damage to the welding area and then the two pipes should be immediately connected. The two pipes are slowly connected to each other. Conversion should take a short time, otherwise it will damage welding quality. Conversion time is noted in the fourth row of Table 2.

7. Welding

Two pipe surfaces approach each other with an approximate speed of 0. The pressure is then increased to a maximum permissible limit after an interval specified in the fifth row of Table 2. The pressure required for welding is 0.015 N/mm².

8. Cooling

A constant welding pressure is maintained during cooling (fifth row of Table 2). After completion of all butt fusion stages, the shape in Fig. 3 should be formed at welding site. Figure 4 shows welding stages on the diagram.