Phased Array Ultrasonic Testing (PAUT) is an advanced non-destructive testing method that uses an array of small ultrasonic elements whose timing (phasing) is controlled by software. By steering, focusing and sweeping the beam electronically, PAUT produces real-time cross-sectional images of pipe walls and welds without moving the probe mechanically — making it especially powerful for piping inspection.
Why PAUT for pipes?
PAUT is widely used on piping because it combines speed, coverage and high resolution. Compared with single-element manual UT or radiography (RT), PAUT can:
- scan a full weld profile and surrounding heat-affected zone in one pass,
- detect, locate and size common defects (lack of fusion, root/ toe cracks, porosity, laminations), and
- produce permanent electronic records (A-, B- and sectorial scans) for trend analysis and fitness-for-service decisions.
Common pipe applications
Typical PAUT applications on piping include girth-weld inspection (construction and field repairs), socket and branch welds, corrosion/erosion mapping (wall-thinning), and weld root/overlay examinations in high-risk systems (pressure piping, pipelines, process piping). Automated and semi-automated PAUT setups are often used for circumferential scans on pipe spools and in-service girth welds to ensure 100% coverage.
Standards & personnel
Industry codes and client specifications increasingly accept PAUT as an alternative to RT/ manual UT for piping welds, but compliance requires following national and international documents (ASME Section V/Article on ultrasonic exam practices, API/ISO guidance and pipeline-specific standards). Qualified operators and procedure qualification (calibration blocks, focal laws, DAC/TCG or TOFD combinations) are essential for reliable results. Many standards also specify personnel training, practical demonstration and documentation requirements. (
Best practices and limitations
Best practice is to prepare a clear scan plan (wedge selection, angles, focal laws), use appropriate calibration blocks (IIW/ASME style) and pair PAUT with complementary techniques (TOFD for accurate sizing where needed). Limitations include sensitivity to surface coupling, complex geometry effects (saddles, fillets), and the need for experienced interpretation — poor setup or under-qualified analysts can produce false calls or missed indications.
Takeaway
For pipework where safety, traceability and defect characterization matter, PAUT is a leading NDT choice: it reduces reliance on radiation, increases inspection throughput and produces rich, reviewable data — provided procedures, equipment and personnel are correctly qualified and the method is used within recognized standards.
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