Thermal　fusion　welding　is　a　common　method　for　high-density　polyethylene　(HDPE)　pipelines.　However,　defects　are　easy　to　occur　at　the　joints　in　the　welding　process,　causing　hidden　danger.　In　this　study,　HDPE　pipes　with　thermal　fusion　welding　defects　were　made　and　the　X-ray　technology　was　used　for　detection.　The　results　show　that　the　testing　effects　of　different　defects　are　quite　different.　The　X-ray　cannot　detect　cold-welding　defects.　The　weld　seam　of　the　over-welding　in　the　negative　is　narrowed.　Besides,　the　unfilled　holes　collapse　during　welding,　resulting　in　poor　detection　results.　The　filled　holes　can　be　detected.　©　Published　under　licence　by　IOP　Publishing　Ltd.