Automatic Ultrasonic Testing (AUT)
AUT technology has now largely replaced radiographic inspection techniques for the examination of pipeline girth welds and has become the NDE industry-standard examination method for girth weld inspection. AUT systems are able to offer superior quality control and data management during project execution. Some of the main advantages of AUT over radiography are:- Safety to personnel (no radiation).
- Productivity (faster cycle time).
- Improved detection and sizing for planar defects.
- Allows the use of engineering critical assessment (ECA) since defect heights can be measured.
- Flaw depth from the surface can be accurately detected
- AUT systems are computer-based, offering superior analysis and records
- Vertical / through wall defects are better identified and quantified
- Point of Detection (POD) is superior with AUT
- Phased Array Vs. Multiprobe
- Advantages
- Disadvantages
Phased array (PA) involves the use of a single multi-element probe (usually 64 elements) on each side of the weld to emulate the many single crystal probes used singly and in tandem to inspect weldments on the more common multi-probe systems.
Currently, phased array systems are being used well within their potential to simply emulate multi-probe systems. Phased arrays have additional capabilities that are not currently utilized (rasta scans and even sweeping angle scans). When used to emulate multi-probe systems there are advantages and disadvantages
- Single probe on each side of weld means a much smaller scanning unit which is easier to maintain
- Improved flexibility since PA can emulate many probe angles and configurations which is software driven
- Set up can be changed by a simple software change (useful if more than one cal block is required for any reason)
- Welds can be inspected faster
- Massive potential for future development
- Process parameters and inspection results are available immediately after girth weld inspection
- Deficiencies can be offset by adding supplementary probes (e.g. additional TOFD probes)
- Very sensitive to couplant issues (water flow and water temperature)
- Probes are expensive
- Single frequency probe, on a multi-probe system the frequency of each probe is optimized depending on angle and type (e.g. volumetric, TOFD etc.)
- Failure of single elements can be difficult to diagnose
- It is doubtful a phased array can be optimized to the level required for SCR inspection mainly due to the large sizing error and probability of detection issues
- Phased array is limited to approximately 32mm thick material; increased wall thickness would require either a longer probe with more elements or two 64 element probes on each side of the weld
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