Tube flaw detecting method using two probes

A tube flaw detecting method for detecting a circumferentially extending crack in a furnace tube mounted on a furnace wall, the furnace tube having a tube wall, a tube inner surface, a tube outer surface, a furnace inner side directed toward the inside of a furnace, a furnace outer side directed toward the outside of the furnace and the furnace wall, and a tube axis, and said method comprising:

• disposing a transmitter probe and a receiver probe so that said transmitter probe and said receiver probe are juxtaposed in a circumferential direction of the furnace tube on the furnace inner side of the furnace tube;
• propagating an ultrasonic transverse wave with the transmitter probe so that the ultrasonic transverse wave enters the tube wall with an angle of 10.degree. to 50.degree. relative to the tube axis and an angle of refraction of 40.degree. to 75.degree. and propagates in a spiral direction of the furnace tube in the tube wall such that the ultrasonic transverse wave travels both circumferentially of the furnace tube through the tube wall and axially through the tube wall of the furnace tube, repeatedly reflecting at the tube inner surface and the tube outer surface, so as to be able to reach a crack that might extend in the circumferential direction on the furnace outer side of the furnace tube;
• and
• detecting ultrasonic waves with the receiver probe so that an ultrasonic wave reflected from the crack on the furnace outer side of the furnace tube that extends in the circumferential direction of the furnace tube to propagate on an opposite side of the furnace tube from the transmitter probe is detected by the receiver probe.

A tube flaw detecting method for detecting an axially extending crack in a furnace tube, the furnace tube having a tube wall, a tube inner surface, a tube outer surface, a furnace inner side, a furnace outer side and a tube axis, and said method comprising:

• disposing a transmitter probe and a receiver probe so that said transmitter probe and said receiver probe are axially spaced apart from each other on the furnace inner side of the furnace tube;
• propagating an ultrasonic transverse wave with the transmitter probe so that the ultrasonic transverse wave enters the tube wall with an angle of 40.degree. to 80.degree. relative to the tube axis and an angle of refraction of 40.degree. to 75.degree. and propagates in a spiral direction of the furnace tube in the tube wall such that the ultrasonic transverse wave travels both circumferentially of the furnace tube through the tube wall and axially through the tube wall of the furnace tube, repeatedly reflecting at the tube inner surface and the tube outer surface, so as to be able to reach a crack that might extend in an axial direction on the furnace outer side of the tube;
• and
• detecting ultrasonic waves with the receiver probe so that an ultrasonic wave reflected from the crack to propagate on the same side of the tube as the transmitter probe is detected by the receiver probe.

A tube flaw detecting method for detecting an axially extending crack in a furnace tube mounted on a furnace wall, the furnace tube having a tube wall, a tube inner surface, a tube outer surface, a furnace inner side directed toward the inside of a furnace, a furnace outer side directed toward the outside of the furnace and the furnace wall, and a tube axis, and said method comprising:

• disposing a transmitter probe and a receiver probe so that said transmitter probe and said receiver probe are axially spaced apart from each other on the furnace inner side of the furnace tube;
• propagating an ultrasonic transverse wave with the transmitter probe so that the ultrasonic transverse wave enters the tube wall with an angle of 40.degree. to 80.degree. relative to the tube axis and an angle of refraction of 40.degree. to 75.degree. and propagates in a spiral direction of the furnace tube in the tube wall such that the ultrasonic transverse wave travels both circumferentially of the furnace tube through the tube wall and axially through the tube wall of the furnace tube, repeatedly reflecting at the furnace tube inner surface and the furnace tube outer surface, so as to be able to reach a crack that might extend in an axial direction on the furnace outer side of the furnace tube;
• and
• detecting ultrasonic waves with the receiver probe so that an ultrasonic wave reflected from the crack on the furnace outer side of the furnace tube that extends in the axial direction of the tube to propagate on an opposite side of the furnace tube from the transmitter probe is detected by the receiver probe.