Titanium heat exchanger tubes used in a wastewater environment at about 150 C for about seven
years have been investigated. As can be predicted, no corrosion was observed on the inner surface of the
tubes, but titanium hydrides were locally formed on the wastewater side (i.e., outer surface) of the tube.
Most of titanium hydrides on the outer surface were observed on the outer surface of the tube contacted
with the baffle plate and the tube sheet. Therefore, it is suggested that hydrogen generates and absorbs at
the outer surface of the tubes contacted with the plate and the sheet.
A hydrogen absorption test has been carried out in the laboratory by scratching a titanium tube while
immersed in water or a sodium sulfate solution. It is considered that the titanium oxide film on the tube
is destroyed through contact with the baffle plate, and thereby the corrosion potential of titanium
decreases to the region at which hydrogen generates easily.