Advanced Ultrasonic Mapping

_{(Advance Testing)}
Advanced Ultrasonic Mapping

By using the standard ultrasonic probes used for pulse-echo thickness measurement and weld inspection with a position encoded scanner device and appropriate software, images of flaws can be generated and electronically saved. Imaging systems provide a highly repeatable inspection and are capable of showing the extent of scan coverage. Due to their ability to store data, they can be used to “fingerprint” a component for comparison with any repeat inspections.

Programmed parameters such as material velocity and beam angles are used in conjunction with positional data to automatically plot flaw responses in the correct position on top, side and end view images showing the volume of material inspected. Many different systems are commercially available, offering two or three dimensional images. Each image view is known by a particular name as follows:

C-Scan image

This is another name for a top (or plan) view image. C-Scans can be obtained from immersion testing systems (where a 0° compression wave probe is scanned across an area through a water path, i.e. non-contact scanning) or from direct 0° contact scans.

Depending on the mode of operation selected, the colour coding levels on the image may represent signal amplitude or range. The latter case is used for automated corrosion mapping where on-screen cursors can be used to show the thickness at any point and sectional thickness plots.

B-Scan and D-Scan images

These images are usually through-thickness side and end view slices which are produced by scanning a probe beam in a linear fashion across an area of interest. The B scan is normally used as a transverse section through a weld and is taken in the scanning direction whereas the D scan is a longitudinal view and is taken in the index direction which is orthogonal to the scanning direction. The B-Scan image is normally acquired through a flaw where it has its greatest through-wall extent and provides an estimate of both remaining ligament and height. As the probe is moved, the A-Scan signals are recorded and plotted according to probe position, range and probe angle. Owing to the beam divergence, the response from a point reflector (e.g. pore) will be plotted along the beam axis even when it does not lie on it, causing arc shaped indications on the B-Scan image. These characteristic arcs vary in shape and size according to the width of the ultrasonic beam at different depths within the material.

Some of the more advanced imaging systems are also capable of generating an amplitude colour coded side view image and of storing all of the raw A-Scan data acquired. For automated scans, individual probes can either be “raster” scanned in the conventional manner, focused at a fixed stand-off (thereby targeting a particular depth zone) or part of a Phased Array.

What will it find

Manufacturing flaws (lack of sidewall fusion, lack of root penetration, lack of root fusion, porosity, etc.), in-service flaws (fatigue cracking, stress corrosion cracking, corrosion, erosion, etc.) and parent material flaws (inclusions and laminations).

Where is it used

Thickness surveys and parent plate or weld inspection on ferritic and non-ferritic pressure vessels, pipework, storage tanks, bridge structures, etc.