The Ultrasonic technique has some particularly useful advantages when used for tubular inspection i.e.
1. High Sensitivity. Allowing very small imperfections to be detected
2. Good penetration power. Allowing the inspection of thick sections
3. Accurate determination of imperfection position and estimation of imperfection severity.
4. Fast response time. Permitting high speed automatic testing.
5. One surface access. Access is required to only one surface of the product being inspected.
Most of the available automated ultrasonic test systems make full use of these attributes by using mainly the pulse-echo technique for defect detection; The following schematic Fig 1 shows this principle.
The gated area is the point in time after the initial transmitter pulse when a return echo from any imperfection would arrive. Note the different positions of the internal and external gates due to the different transit times for reflections from internal and external imperfections.
The ultrasonic pulse echo method can also be used to measure physical parameters of the tube under test; the schematic figure 2 shows the principle of measuring wall thickness.