(MENAFN Press) Sittard, the Netherlands “ May 7, 2012 “ SABIC has developed a new method for high-speed evaluation of the slow crack growth resistance of high density polyethylene (HDPE) used for pressure pipes. The method will enable processors to benefit more quickly from new developments in general in HDPE for pipes, by cutting the time taken to bring a new material from the laboratory to the market.
SABIC is convinced that the widespread acceptance of its Strain Hardening Test Method will accelerate adoption of its latest SABIC Vestolen A RELY grades of bimodal HDPE for high pressure pipe.
The Strain Hardening Method is faster and more cost-efficient than traditional methods of obtaining data on long-term performance in pipes. In addition, it requires neither a special notched specimen nor detergents. "It is easy to implement in laboratories, is suitable in the development of new grades by researchers, and also very valuable as a batch release test for resin suppliers. It is a method that saves time, money and energy," says Lada Kurelec, Technical Marketing Manager for HDPE at SABIC.
The international quality authority Kiwa Technology, based in Apeldoorn, The Netherlands, has adopted the method. "We have found that the Strain Hardening test delivers reproducible results which very nicely correlate with results of time-consuming traditional slow crack growth tests - but in a much shorter time," says Frans Scholten, Expert on Material Testing at KIWA Technology. "We use the test to quickly provide pipeline owners with relevant information about the long-term quality of their existing polyethylene gas and water distribution networks. Moreover, we provide resin manufacturers with the opportunity to compare the relative quality of development resins with other products."
Traditional methods for assessing long-term behaviour in pressure pipes like the Full Notch Creep Test (FNCT) and Notched Pipe test are measured in months and sometimes years. The tests are costly, and their reliability is uncertain. Using traditional notch tests, it would take many months to prove that a new material meets, for example, the highly-demanding requirements of PAS 1075. The Strain Hardening Method allows that time to be slashed to a few hours, requiring a simple tensile test at 80C. Further advantages of this test method are very low measurement variation, absence of surfactants and notches, and the small amount of required testing material (< 50 g).
According to SABIC's Lada Kurelec, SABIC went back to basics to develop the new test. "Strain Hardening is based on fundamental postulates of crack propagation," says Kurelec. "SABIC is analysing the basic polymer properties that give rise to stress crack resistance. This is a fundamentally different way of obtaining the information needed to show pipes will perform to typical requirement for many decades."
In recent years, an increasing number of countries in Europe have begun adopting even tougher requirements for pressure pipe, as laid down in the PAS 1075, a so-called Publicly Accessible Standard. This requires even higher resistance to slow crack growth (SCG) than is called for in the PE 100 specification.
The move comes as a result of the increased use of new trenchless pipe installation methods such as guided boring and horizontal directional drilling; these methods have a very positive impact on the environment, but they pose higher demand on pipe properties, due to potentially higher surface damage which can ultimately lead to prior pipe deterioration.
The new generation of pipe materials with an enhanced slow crack growth resistance, like SABIC Vestolen A RELY 5922 are the right solution for such typical applications.
SABIC is strongly involved in the initiatives to use the Strain Hardening Method as a standard test method for the pipe industry by test institutes in Europe and around the world.
SABIC will be at IFAT Entsorga (Hall B6, Stand 511), the world's premier trade show for innovations and services in water, sewage, waste and raw materials management, being held in Munich, Germany from May 7 to 11.
