Austenitic　stainless　steels　are　widely　used　in　key　components　of　major　equipment,　and　welds　are　weak　parts　of　the　entire　equipment.　Ultrasonic　wave　have　propagated　in　Austenitic　stainless　steels　welds　with　the　multi-path　and　multi-mode　propagation　characteristics.　So　the　multi-mode　ultrasonic　phased　array　detection　method　for　austenitic　stainless　steel　small　diameter　pipe　welds　is　studied.　The　detection　ability　of　four　different　direct　wave　inspection　modes　and　eight　different　primary　reflection　wave　inspection　modes　for　typical　defects　in　small　diameter　pipe　welds　are　compared　and　analyzed　by　numerical　simulation.　A　fusion　imaging　method　is　developed　based　on　a　preferred　direct　wave　detection　mode　and　a　bottom　surface　primary　reflection　detection　mode.　On　this　basis,　weld　defect　detection　experiment　is　carried　out　on　the　austenitic　stainless　steel　small　diameter　pipe.　The　results　show　that　the　multi-mode　fusion　imaging　method　can　realize　the　detection　of　multiple　defects　in　small　diameter　tubes　well.　Compared　with　single　mode　total　focusing　imaging　method,　the　fusion　imaging　method　can　not　only　improve　the　signal-to-noise　ratio　of　imaging,　but　also　greatly　reduce　the　generation　of　artifacts.　The　project　research　work　provides　a　feasible　technical　solution　for　the　inspection　of　austenitic　stainless　steel　small　diameter　pipe　welds.　©　2020　Journal　of　Mechanical　Engineering.