Failure Investigation of Titanium Condenser Tubes

Abstract

Losses due to condenser tube leaks, fouling, and failures lead to higher nuclear power generation costs due to increased maintenance and loss of production. Recently, a distinctive form of degradation was observed in condenser tubes made from a commercially pure titanium alloy. Helium leak tests, eddy current inspections, and borescope inspections conducted in the field revealed through wall cracking around the tube circumference of the affected tubes.No indications of embrittlement due to titanium hydrates or defects were found in the microstructure of the failed section. Flattening test results confirmed the high ductility of the failed tube. Metallurgical failure analysis revealed fatigue cracking at the location of the seam weld that led to tube failure. This was caused by vibration/movement of the tube during service. Scanning electron microscope examination revealed trans-granular cracking and the presence of striations on the opened crack surfaces of the titanium tube section, which is consistent with fatigue cracking. It has been postulated that the high cycle fatigue due to flow induced vibration along with steam dump impact led to cracking.