Numerical Assessment of PE 80 and PE 100 Pipe Lifetime Based on Paris‐Erdogan Equation

Abstract

Summary: A novel accelerated fracture mechanics extrapolation procedure based on cyclic test with cracked round bar (CRB) specimens was verified by a correlation of real pipe failure time to simulated failure times at a temperature of 60 °C. The procedure was applied to predict the long‐term failure of modern PE 80 and PE 100 pipes 23 °C. Moreover, the used stress intensity factor concept also allows to consider the impact of arbitrary additional loading situations like soil loads or point loads and to assess pipe lifetime under complex loading situations.

On crack propagation in the welded polyolefin pipes with and without the presence of weld beads

“…Lifetime of the homogenous pipe in this case is realistic and corresponds well with simulations of the lifetime published [4,30]. The effect of the weld bead is slightly positive in both modes of failure by the axial crack and by the circumferential crack as well.…”

“…In case of the polymer weld, due to the weld bead development a typical defect size increases and values higher than would be relevant. Material properties of PE 100 were estimated experimentally by Frank et al[30] ( and ). It is shown that the resulting lifetime is strongly sensitive to the initial defect size ( ) and a small increase in the defect size dramatically decreases the lifetime of the structure, see the difference in Figs 26,…”

Direct comparison of the compliance method with optical tracking of fatigue crack propagation in polymers

“…[6,17] Inspired by these excellent results, the method was adopted to determine fracture characteristics for other materials that are not linear elastic and isotropic, such as bone [18][19][20][21] and polymers, including reinforced [22,23] and nonreinforced thermoplastics, [24], which includes ultra-high molecular weight polyethylene [25,26] and polyethylene pipe grades. [27][28][29][30] It is not trivial to apply a method developed for linear elastic behaviour on non-linear, time dependent materials where the (apparent) modulus strongly depends on loading conditions and loading time. Modifications of the method were, therefore, proposed; e.g.…”

Physical background of the endurance limit in poly(ether ether ketone)

“…For many polymer systems, both glassy and semicrystalline, unfilled and fiber reinforced, it has been demonstrated that, at the same value of the maximum load, application of a high amplitude cyclic load will promote crack‐growth and drastically reduce the failure time compared to that observed in static loading . In the case of polymers with a very high resistance to crack growth, it is, nevertheless, not uncommon that crack‐growth dominated failure is not observed during characterization experiments; a prime example being the absence of crack‐growth dominated failure in current polyethylene (PE) pipe grades during certification testing . The fact that crack‐growth dominated failure is not observed during static tests of over a year only implies that the material is very crack resistant; it will definitely appear at lower loads and longer loading times.…”