For commercial metal structures requiring non-destructive testing, Phased Array Ultrasonic Testing (PAUT) is emerging as the next-generation methodology of choice for its compelling advantages in time and cost savings, quality and accuracy, as well as in compliance and reporting.
Phased Array Ultrasonics is similar to a sonogram or ultrasound used in a hospital—except the PAUT machinery is small enough that it can be brought to the material for examination, rather than the material brought to it. The average PAUT machine would fit in a backpack and weighs about 20 pounds.
In contrast, the massive size of the hospital’s testing machinery, and health industry protocols, still have us going to local health centers to be scanned. The similarity is that this advanced ultrasonic testing produces detailed images of internal structures that are then interpreted by experienced, trained technicians.
More than 100 years ago, radiography was a massive advance in structural flaw detection when visual inspection had been the only option.
In operation, a PAUT transducer—an electronic device that converts energy from one form to another (like LEDs are transducers of electricity to light)—emits multiple beams at many angles at once, more like the sweep of a flashlight than the single stream of a laser, over a structure or weld.
This creates more enhanced coverage and detail than that produced by predecessor methodologies in revealing defects hidden inside the material.
With PAUT, you can scan multiple angles at once, record the entire scan and analyze the data at any time all of which greatly improves the ability to quickly and accurately identify flaws or inconsistencies.
The Evolution in Non-Destructive Examination (NDE) Testing
While gaining in adoption, PAUT still is not as common as traditional methodologies like conventional ultrasonic testing and radiography but has compelling advantages over these and other approaches in precision and quality, speed, safety, compliance and reporting as well as in time and cost savings.
More than 100 years ago, radiography was a massive advance in structural flaw detection when visual inspection had been the only option. This technology came along shortly following the discovery of X-rays in the late 1800s, and quickly developed as the commonly accepted NDE method. Still in use today, radiography uses X-rays to create an image of a material’s interior, allowing engineers to identify defects hidden within.
About 20 years after radiography came into practice, ultrasonic testing (UT) developed into a leading application for NDE. UT sends sound waves through one surface of the material that are then reflected back to the same receiver. The imperfections reflected back indicate the location of flaws.
Other methodologies, like magnetic particle and dye penetrant testing, came along to join visual testing disciplines to detect surface or near-surface flaws only.
Mid-20th century advances in digital technology transformed NDE testing with the development of high-resolution images that could be manipulated and analyzed using computer software. Computer-aided UT enabled engineers to automate inspection processes, improving accuracy and reducing human error. PAUT is an advance on conventional ultrasonic testing.
PAUT’s Performance Advantages Over the Others
PAUT eliminates all the negatives associated with radiography testing such as the need for hazardous materials like radioactive isotopes and establishing radiation zones, which requires shutting down any other activity in the vicinity. PAUT is a safer choice for the technicians, other property users and the environment, and normal site operations can continue.
Conventional UT is accurate but slower than PAUT as you can only scan one angle at a time, usually limited to three specific angles. With PAUT, you can scan multiple angles at once, from only one angle and often up to 64, throughout the spectrum used for flaw detection, generating detailed 3D imagery. All the data is recorded and can be accessed at any time.
Radiography is accurate and can inspect large sections at a time, but you only get a two-dimensional shot of the weld. With PAUT you also get depth. This matters in repairing thicker welds. In the case of a 4-inch weld, PAUT can identify which side of the weld to come from to make the repair whereas radiography cannot. If the repair is 1 inch deep and you come at it from the wrong side, you could be removing 3 inches of weld instead of 1 inch—costly in time and budget.
Radiography also interrupts the flow of other workers on the job due to its safety-related restrictions and, because of its limited two-dimensional image, can make it a guessing game on deep weld repairs as to which side to approach.
Case study: Salt Lake City Temple project
In 2019, the Church of Jesus Christ of Latter-day Saints initiated the largest preservation project ever undertaken of its historic Salt Lake City Temple—a complete seismic upgrade of the Temple that first opened in 1893.
In October 2024, The Desert News quoted Brent Roberts, managing director of the Special Projects Department of The Church of Jesus Christ of Latter-day Saints, as saying it scared him when he read first read, in 2001, a seismic report on the stability of the historic structure—for two reasons: the Temple would not survive a significant earthquake and, the technology did not then exist to do anything about it.1
Twenty years later, PAUT technology is one of the innovations being used to make the Temple more seismically resilient. More than 60 48-inch and multiple 80-inch pipes are being installed. Using conventional UT for NDE testing would take about a day per 48-inch pipe versus two hours using PAUT. Applying this difference to 60 such pipes and using PAUT saves six hours per pipe—360 hours or 45, eight-hour days.
What to Look for in PAUT Providers
Certified technicians providing UT and PAUT NDE testing must have more than 1,000 hours of training and field experience to be certified. From an NDT trainee to Level III certification, these technicians build the skills and competencies required to perform the inspection process, accurately interpret the images and generate complete and accurate documentation of results. The American Society for Nondestructive Testing governs requirements for these certifications.
Phased Array Ultrasonics is the emerging choice for non-destructive testing in commercial metal buildings. Its advantages in safety, quality, cost savings and methods that align with stringent industry standards and regulations make it a valuable tool for building owners and decision-makers.
By understanding its applications and benefits, and by selecting experienced and certified providers, stakeholders can ensure the structural integrity and safety of their metal buildings.
Michael A. Bobinchuck is the National Manager, NDT Services with Terracon in the Salt Lake City, Utah, office. He has more than 20 years’ experience and is Certified Welding Inspector (CWI), ASNT Level III in Ultrasound, Visual, Dye Penetrant and Magnetic Particle Testing, AWS D1.8 seismic UT certified, Phased Array Ultrasonic Testing, NDE ACCP Level II Inspector in VT, UT, MT, and PT, NACE Level I Coatings Inspector and a Senior Construction Inspector.
