Papers # 2014 Chicago
As the resistance to notches of the new PE 100 RC materials continuously improves, the classical control methods - as mentioned in the product standards - of PE have to improve consequently. Indeed, the resin compound producers now have pipe qualities with notch resistance far beyond 1000 h. It was necessary to “look” for a new accelerated test method, in order to evaluate the several production runs of the compound and pipe producers in a time frame of one week. The notch test according to ISO 13479 is specifically applicable to PE 80 and PE 100 pipes. But PE 100 pipes with extension RC (resistant to cracks) are difficult to evaluate in a quick way according to this standard and the requirements as laid down in the products standards EN 1555. Therefore, an alternative test method was necessary to judge the resistance to notches (SCG-slow crack growth) of these RC-materials. In Germany (Dr. Hessel J. (D)) an alternative test method on small test specimen machined out of the PE pipes with circumferential notches, has already been developed. The notched specimen is submerged in a tension-active agent (called NM5), which accelerates the crack speed of the notch. As the composition of NM5 is not exactly known, BECETEL proposes to adapt the well known notch-test according to ISO 13479, by using an accelerator. This method is called PANT (Pipe Accelerated Notch Test) and is directly applicable on the notched pipes at room temperature. Another advantage is that pipe stresses remain in the pipe and the preparation of the notches according to ISO 13479 remains the same. In practise, it is sufficient to apply the accelerator on the four notches and not on the whole pressurized pipe, as the chemical does not attack the PE-pipe itself but only the notched region, which is under higher stress. Moreover tests have shown that it is not necessary to test at elevated temperatures, which means that test temperatures at 20 °C ± 1 °C are sufficient. Nevertheless super acceleration and short test times can be obtained using higher temperatures and or other accelerators.