When testing tubing with an encircling coil, the phase relationship of the output signals from identical discontinuities is:

In Eddy Current Testing, when using an encircling coil to test tubing, the effective measurement and signal interpretation from discontinuities can be analyzed through their phase relationships. For identical discontinuities located on the outer diameter (OD) and the inner diameter (ID) of the tubing, there is a distinctive behavior in how the signals are generated.

When a discontinuity exists at the OD, the Eddy currents are induced in a way that causes a particular phase response in the signal. Due to the geometric positioning of the coil and the nature of the electromagnetic fields generated, the discontinuity located at the OD influences the phase of the signal transmitted from the encircling coil leader first. Conversely, for an ID discontinuity, the signal experiences a different induction effect, leading it to lag behind the OD signal.

This results in the phase shift between the signals from the two discontinuities where the signal from the OD discontinuity leads the signal from the ID discontinuity. Understanding this phase relationship is critical for interpreting the results accurately during testing.

Recognizing the significance of phase differences is essential for interpreting signals and ensuring accurate defect characterization within the tubing material being tested.