As　a　common　welding　method　for　polyethylene　natural　gas　pipelines,　electro-fusion　welding　has　been　widely　used.　However,　defects　are　easy　to　occur　in　the　fusion　area　during　the　welding.　In　this　paper,　high-density　polyethylene　(HDPE)　pipes　with　different　types　of　electric　welding　joint　defects　are　processed,　and　the　detection　effect　of　the　ultrasonic　phased　array　on　joint　defects　is　explored.　The　results　show　that:　Ultrasonic　phased　array　detection　technology　is　easy　to　operate　and　reliable.　It　can　detect　three　common　defects:　inadequate　socket,　cold　welding,　and　scratch　of　oxide　scale.　In　addition,　according　to　the　inspection　result　chart,　the　defect　type　can　be　accurately　judged.　©　Published　under　licence　by　IOP　Publishing　Ltd.