Mark J. Lamborn, Pam L. Maeger, Rick E. Kunc, Vivek Rohatgi, Paul J. DesLauriers, Ashish M. Sukhadia
Papers # 2014 Chicago
Dual cooling is a post-extrusion cool down process employed for polyethylene (PE) pipe, whereby either water or ambient air is forced through the pipe bore following extrusion, in order to accelerate cooling. The primary benefits offered by the dual cooling process are increased production rates and reduced resin slump. Although the dual cooling process provides some obvious advantages, it may be associated with reduced rapid crack propagation (RCP) performance, primarily due to increased levels of residual stress. The current study addresses the effects of a dual cooling process on the RCP performance of PE pipe, as measured by the small scale steady state (S4) test; here, the dual cooling process considered is one that uses forced air to cool the pipe’s interior bore following extrusion. The results of a finite element analysis (FEA) of heat transfer during the dual cooling process are examined in combination with experimental measurements of residual stresses and S4 critical pressures for PE pipe, in an effort to provide an understanding of how the dual cooling process affects RCP performance. Analysis of the FEA and experimental results suggest that the magnitude of the effects of forced air dual cooling on RCP performance may depend on both the density and the characteristic relaxation time of the pipe resin. The results of the FEA and experimental program are discussed in detail and conclusions provided.