Abstract: Apparatus, methods, and articles of manufacture for monitoring a condition of a material are disclosed. In particular, the example apparatus, methods, and articles of manufacture emit a first acoustic signal into a wall of the tubular member having a first temperature value and obtain a first propagation time associated with the first acoustic signal. In addition, a second acoustic signal is emitted into the wall having a second temperature value and a second propagation time associated with the second ultrasonic acoustic signal is obtained. The second temperature value is determined based on the first temperature value and the first and second propagation times.

Abstract: Apparatus, methods, and articles of manufacture for monitoring a condition of a cavity surface of an elongated member having a cavity therein. In particular, the example apparatus, methods, and articles of manufacture emit a first ultrasonic signal that propagates from a first surface of an elongated member having a cavity therein toward a second surface of the cavity having a first temperature value. First and second echoes associated with the first ultrasonic signal are then obtained. At least one of the first and second echoes is associated with a recess in the second surface. A condition of the second surface is monitored by determining a second temperature value of the second surface based on the first and second echoes and the first temperature value.