Environmental stress cracking of chemically aged HDPE-100 gas pipe under impact fracture mode

High-density polyethylene (HDPE) pipes are widely employed for urban gas, water and sewage transportation networks because of economic considerations and very satisfactory lifetimes. As they are straight forwardly designated for numerous hostile conditions, the stress cracking resistance needs to be investigated in combination with ageing in controlled environments. This study is set to investigate long-term sorption experiments followed by Charpy fracture tests using the same arc-shaped specimens machined from HDPE pipe. Chemically ageing media are deionized water (DW) and both hydrochloric (HA) and acetic acids (AA). For the first 4 weeks, it is found that % weight change increased drastically for HA medium. Then, for the next 30 weeks period, the inverse situation took place as the % weight change for HA diminished tending nearly to zero while it augmented for DW and AA environments. Within the first week, the impact fracture energy of HDPE decreased for all media and then increased substantially for both acids well above the as-received (AR) reference line. Charpy energy experienced a monotonic decrease for DW as swelling enhancement is promoted in the absence of plasticized material. After 7 months ageing, both acids show much higher Charpy energies than AR and DW specimens and a substantial increase in ductility. The resilience changes with respect to AR tests are respectively +110%, +75% and –25.8% for HA, AA and DW. It is accepted that strong acids (i.e., HA) easily deplete antioxidants and carbon black mixed with the resin. The combined effects of both mechanical and chemical processes can serve a more representative durability studies of HDPE pipes including ESC phenomenon.