Fortunately, in this second occurrence, the damage involved only the machine not human life. Subsequently, the Bently Nevada thrust monitors were finally connected to automatic shutdown without any intervening temperature voting. This axial rub effectively unloads the thrust bearing by allowing the rubbing parts to absorb some of the thrust load. In this case, the thrust bearing pads will actually decrease in temperature as the bearing failure progresses, and will not always go through a high enough temperature to initiate any temperature alarms. These do not necessarily result in a failure mechanism where a pad becomes more heavily loaded and its temperature increases.
Axial position is a much more reliable indicator of thrust bearing problems.
Depending on where the temperature sensors are embedded in the thrust bearing pads, large differences in temperature can occur over the pad's geometry. For example, a pad will generally experience the highest temperatures at the edge of the pad where most of the load is carried. Temperature variations of 40 or 50 degrees F are not uncommon across a pad. Thus, a pad could experience significant heating during a failure, but the location of the temperature sensing element may not always capture the true temperature at the place where Babbitt is breaking down or load is most concentrated. This means that Babbitt could be melting at one edge of a pad, yet temperatures could be much lower even normal at the other edge of a pad.