Slow Crack Growth of Polyethylene—Accelerated and Alternative Test Methods

Assessing the integrity of in service polyethylene pipes

“…Understanding the failure behaviour of PE pipes is important in assessing their long term safety and performance. Generally, there are 3 distinct failure modes in PE pipes [1][2][3][4][5][6]. At higher stress levels, PE will undergo delayed ductile failure due to the local yield stress being exceeded [4][5][6].…”

“…Appropriate engineering design should be utilized to avoid this kind of failure [1,3,5]. The second failure mode is quasi-brittle failure which proceeds via a "Slow Crack Growth" (SCG) failure mechanism, and is the most common observed in pipe failure [1][2][3][4][5][6][7]. The last failure mode is known as "brittle failure", which is observed after a long period of service time when the PE begins to breakdown due to ageing and degradation.…”

“…The service life of a PE pipe is often taken as the time before quasi-brittle failure occurs, and hence the slow crack growth resistance of the PE is a key performance indicator [12][13][14]. Ascertaining the resistance to SCG of PE resins via laboratory based tests is commonplace and, consequently, there are a substantial number of studies measuring slow crack growth of PE resins [2,[15][16][17][18]. The study of the remaining lifetime of PE pipes that have already been used in service is less common [19,20].…”

“…The CRB uses cyclic loading instead of elevated temperature to accelerate the test, allowing these newer grades of PE to be tested in substantially shorter times [20]. The CRB test has been used in several studies to clearly distinguish different times to failure for various PE80 and PE100 pipe material grades [2,19,20,25,31]. While many benefits exist with using the CRB test to ascertain time to failure of PE pipes, some limitations do exist.…”

Linking Antioxidant Depletion with Material Properties for Polyethylene Pipes Resins

“…Polyethylene (PE) is commonly used in gas distribution and water distribution networks, with the popularity of PE for these applications being due largely to its low cost and corrosion resistance . Over the years, significant resin development has seen improvements in the mechanical properties of PE, most notably the slow crack growth (SCG) resistance . Resin development has seen both high molecular weight and medium molecular weight PE be used with single and bimodal molecular weight distribution.…”