國內某工廠進行大型碳鋼管件之銲接組裝過程中，因工件幾何形狀複雜，使銲接施工不易，銲後以超音波探傷檢測，顯示有明顯缺陷，本研究以銲件金相觀察、硬度量測與彎曲試驗，分析銲件缺陷型態及可能之缺陷肇因。研究顯示，缺陷主要分布於打底銲道的根部、打底銲道層與層間以及熔融線上，為夾渣與熔融線熔合不良所導致，而銲道內部各層銲道間之接合狀況則無其他裂紋發生。硬度量測顯示銲件之母材、熱影響區與銲道皆無異常高的數據，經彎曲測試後，則無任何裂紋產生，顯示整體銲道內部接合狀況良好。因工件幾何形狀複雜導致打底銲道缺陷與熔合不良的狀況，應可透過優化銲接作業程序、銲接人員技術檢定及現場作業管理進行改善。

To weld and assemble large carbon steel pipe is hard due to the complex geometry of the workpiece in a domestic factory. Therefore, Ultrasonic testing was utilized and the results showed the obvious defects after welding. In this study, metallographic observation, hardness measurement and bending test were applied to analyze the type and possible causes of welding defects. Results show that the defects are mainly distributed in the bottom of the root weld bead, between the bottom bead layers, and on the fusion line, while the layers between the inner weld bead have no cracks occurred. These defects were caused by the slag and poor fusion on the fusion line. The hardness measurement shows that the base metal, heat-affected zone and weld metal of the weldment have no abnormally high value. After the bending test, no cracks have occurred, indicating that the condition of overall inner weld beads is good. The defects of root weld bead and poor fusion due to the complex geometry of the workpiece could be improved by optimizing welding procedures, welder’s technical verification and on-site operation management.