Adaptive ultrasonic imaging of electric resistance welded pipeline seams

In the following, the measurement setup, the calibration of the system, and the process of surface detection are described. Images obtained on representative samples are presented for setups in a water tank and with a flexible, water-filled cushion.

A method for the ultrasonic imaging of seam welds has been developed and demonstrated. The approach implements a modification of the adaptive Total Focusing Method for application on seam welds by imaging the outer and inner surface of the pipe sample, followed by imaging of the weld region with shear waves.

Criteria for the detection of the surface from the images were added to increase the robustness of the approach. The accurate calibration of sound velocities and geometrical parameters was found to be essential for the generation of aligned and focused images. In addition to experiments in a water tank, a watertight housing with a flexible membrane was tested successfully. This assembly enables application of the developed approach for larger pieces of pipe in the field that cannot be scanned in a water tank. The extra interface introduced by the membrane was found to have negligible influence on the images. The resulting images allow for detection and accurate sizing and characterization of indications, enabling also the discrimination between critical and benign flaws.

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