An elegant and fast method to predict the slow crack growth behavior of HDPE pipe materials

Session 11A
5:10 pm

Linda Havermans, SABIC

High Density Polyethylene (HDPE) is widely used in the high demanding utility pipes because its versatile properties profile. One of the most prominent properties determining lifetime of HDPE in pipe applications is its resistance to slow crack growth (SCG), which is usually assessed via testing methods such as the notched pipe test, FNCT, PENT.

In the last years, the slow crack growth resistance of HDPE grades has gained increased attention, as it is recognized that control over this property is extremely important in order to secure lifetimes of 50 years and above in the advance of trenchless installation techniques. Nowadays, the European market requirements for HDPE grades used in these applications require measurement times of at least one year (> 8760 hours) for the traditional notch test and FNCT. These extremely long measurement times form a serious concern in using these testing methods for determination of SCG behavior of resins and manufactured pipes. In a market with increasing demands with respect to SCG behavior a fast, regular and reliable test method for quality control of raw materials is an absolute necessity especially for resin producers.

SABIC developed a sophisticated method in which SCG behavior assessed by traditional methods (e.g. FNCT) is correlated to the strain hardening modulus of polyethylene, determined from a simple tensile test at 80 C. Advantages of this test method are the very low measurement variation, absence of surfactants and notches, the limited amount of required testing material (< 50 g) and, above all, testing times of only a few hours. Moreover, the use of a universal test set up allows for an easy and cost effective implementation at all accredited testing laboratories for HDPE pressure pipe applications.

Over the last two years, SABIC has carried out extensive work in finalizing the correlation between the strain hardening modulus and traditional methods (e.g. FNCT) and found an excellent correlation. This correlation expresses the value of this elegant technique as a short term test for resin development, batch release of high performance HDPE pipe grades and reduction of analysis costs.

Linda Havermans*, Rudy Deblieck†, Mary McCarthy*, Rainer Kloth*, Lada Kurelec*
*SABIC, The Netherlands, †DSM Resolve, The Netherlands