Development of Crack Growth Curves and Correlation to Sustained Pressure Test Results for Cell Classification 445574C High Density Polyethylene Pipe Material

Code Case N755-1 of the ASME Boiler and Pressure Vessel Code, Section III, Division 1 Code currently permits the use of high density polyethylene (HDPE) in buried Safety Class 3 piping systems. There have been concerns with the Slow Crack Growth (SCG) of HDPE emanating from scratches that may occur during fabrication or installation. The possible use of tensile coupon tests for determining the life span of the pipe with surface scratches could provide a more cost effective testing method than does the use of sustained pressurized crack pipe tests. This paper presents the results of further investigation into the SCG rates of notched PE 4710 HDPE pipe made from a cell classification 445574C bimodal resin. The da/dt versus K_I curves were developed from notched coupon testing. Standard fracture methods were then used to predict the failure time of the notched pressurized pipe specimens subjected to long-term hydraulic stress. The results for the SCG depth of the externally notched sustained pressurized pipe tests are provided along with the notched coupon test results. The actual failure times of the notched pressurized pipe tests are compared to the predicted failure times for the same specimens.