Forgefix pipe clip double openlock forgefix pcdo22 these forgefix double openlock pipe clips are made from heat resistant polypropylene designed to withstand the temperature changes in central heating systems they are effective with temperatures of up to 100c most pipes in domestic central heating systems operate at around 70c used when fitting most types of pipe work polypropylene also known as polypropene is a thermoplastic polymer used in a wide variety of applications an additi