Reduction of Contaminants

Two pipes heated by roughly the same amount and fused at different pressures will expel different amounts of molten material from the joint interface. For example, a pipe fused at a higher pressure will expel more molten material than the pipe fused at a lower pressure. That being the case, it is possible to assume that if small amounts of a contaminating material (e.g. dust, etc.) are present on the pipe ends, there is a likelihood that they will be expelled with the melt which forms the bead.

In order to test this theory, equal amounts of small brass granules were blown onto heated pipe ends just before joining. These pipes were fused at 0.517MPa (75 psi) and 0.15 MPa (21.75 psi) respectively. After the fused pipe was sufficiently cooled the joints were tested using an ultrasonic (UT) system.

The UT tests seen in Figures 4 and 5 concluded that the high-pressure sample was a better fusion than the low-pressure sample.

The fusions were shaved through with a McElroy facer and brass shavings were seen in the outer bead of the joint fused at 0.517 MPa (75 psi) but none were evident in the joint fused at 0.15 MPa (21.75 psi). Figures 1 through 3 indicate that there were particles of brass that remained in the fusion interface in the 0.15 MPa (21.75 psi) joint but all were expelled in the 0.517 MPa (75 psi) joint.

Cooling Time

As with any medium, different levels of temperature are experienced when heat is applied, with the hottest being closer to the heat source. It is obvious that if fusion occurs at a cooler temperature, but where the molten PE material is still fusible, the time required for the joint to cool to the desired internal temperature will be reduced.

As seen in Figure 6, using conventional fusion methods, the cooling time required for a joint of the same material and wall thickness is shorter when fusing with an interfacial pressure of 0.517 MPa (75 psi) versus 0.15 MPa (21.75 psi).

This testing was performed using 6 inch IPS SDR 11 pipe. Greater savings of cooling time could be expected when fusion joining larger diameter pipes. Since the cooling time is the greater percentage of total time in the fusion process, significant decreases in overall joint production time are experienced while great increases in productivity result in reduced joint cost.

The study unexpectedly found a great a difference in cooling times, which warranted further study. It was decided to test the cooling times in a series of larger diameter pipes with thicker walls.

The set of test pipes included 219mm SDR 11, 324 mm SDR11, 457 mm SDR 11 and 630 mm SDR 9 pipe. Figure 7 shows small holes drilled at the top and bottom of the pipes from the centre of the faced wall of the pipe and at an angle so they would surface on the other side of the clamping jaws. Thermocouples were then fed through the holes then staked into place, exactly in the center of the pipe wall.

The pipes were monitored on removal of the heater and until the hottest area in the interface reached 65° C. Both 80º C and 65º C temperatures were noted even though most material scientists agree that cooling to 80º C is quite satisfactory. The results are shown in Figure 13.

Figure 8 summarises the dramatic differences in cooling times between the types of pipe. Using this information and empirical joining times, the difference in the number of joints per day that could be fused on a typical job can be estimated, shown in Figure 9.

Conclusion

Taking the tremendous savings in cooling time, the contractor can estimate savings in manpower, equipment, and other tangible costs that can be saved. Reducing the installed cost of PE pipes can ensure profitability and coupled with trenchless installation, PE becomes the preferred material for all low and medium pressure piping applications.