99 Diseases of Pressure Equipment: Titanium Hydriding

Titanium (Ti) hydriding is another somewhat unusual metallurgical degradation phenomena that can result in brittle fracture. Unlike many other steel embrittlement phenomena, this one most often occurs in thin wall Ti tubes that have been selected for their superior corrosion resistance of overhead condensers.

In certain pH ranges and under some galvanic corrosion conditions above 165^oF (75^oC), hydrogen penetrates the Ti tube and reacts to form an embrittling hydride phase. It can also occur when iron has contaminated the surface of the titanium tube, thus, promoting a galvanic couple that drives hydrogen into the Ti tube. So, fabrication and repair cleanliness are vital to the avoidance of titanium hydriding. The hydriding reaction may continue until there is a complete loss of ductility, and any form of transient stress can fracture the tubes. Those stresses may occur from upset process conditions or during bundle removal or repairs. Like so many other metallurgical embrittling phases, there may be no reliable inspection techniques to detect titanium hydriding, though some claim to be able to detect it with specialized eddy-current techniques. Typically, an owner-user finds out that their Ti tubes are hydrided by experiencing leaks or cracks. If there is doubt, a tube can be pulled and crushed in a vice to see if it results in a ductile or brittle fracture.

A related phenomena in titanium is metal ignition, which will be covered separately. But in one case, significant Ti hydriding was thought to be a potential contributor to the metal igniting and burning.

Do you have titanium condensers inservice that may be susceptible to titanium hydriding?