目前普遍采用内穿式涡流法对核电机组冷凝器的薄壁钛管换热管进行在役期间的检测，而支撑板处管壁出现凹陷则是在役期间常见的管壁损伤。对支撑板处凹陷的形成机理进行分析，认为是支撑板镗孔内发生腐蚀所致，并对特制的凹陷样管进行涡流检测，通过记录凹陷信号幅值并观察凹陷区域开裂情况，对实际检测中凹陷管的处理标准给出了建议。

Nowadays the inner ET testing is wildly used for in-service inspection of titanium tube of condenser in nuclear power plant. In this paper we analyze the causes of DNT, and consider it is attributed to corrosion inside support plate borehole. We also tested the sample tube with dents by ET tester, we recorded the amplitude of the signal and observed the cracking of the depression, and based on that, we give some suggestions on the treatment standard of the DNT tube in the actual test.