Slow Crack Growth Test [PEX]

This paper presents the results of a series of notch tests on bars and pipes. Tests were performed on PE, PEX (peroxide, silane and radiation), PP and PB resins. The temperature was 80°C. Large differences were observed between the various polyolefin grades. Differences were also observed between different PEX-grades in failure times. The longest slow crack growth failure time was more than 56 times longer than the shortest one. One of the PEXgrades and the PB pipe grade showed very good slow crack growth resistance. When comparing test on notched bars (PENT) with tests on notched pipes (notch pipe test) the failure time for the pipes were always longer than for the PENT. But the qualitative ranking was the same for two PEX-grades. The results show that slow crack growth (SCG) testing can rank different pipe grades. But it is not possible to make a certain general ranking between PEX made from different cross linking methods. Each producer of PEX pipes must ensure the quality of their own pipes, and not rely to a general belief that one cross-linking method is superior to another. This investigation shows that one of the PEX pipes is worse than a typical MDPE pipe in SCG-resistance. At the same time another PEX pipe grade is much better than a typical MDPE pipe in SCG-resistance. Also the polybutylene pipe showed a very good SCGresistance, the same levels as the best PEX pipe.