Wondering About Welds? Phased Array Ultrasonic Testing Provides Answers & Benefits

For the average person, the concept of ultrasound is limited to the doctor’s office or those occasions when proud parents-to-be share a sonogram of their newest family member. But in the industrial world, ultrasonic technology has been used for decades in numerous industries to keep the public safe.

Providing fast and accurate weld inspections is one of the most common industrial uses for ultrasound. Today’s advanced Phased Array Ultrasonic Testing (PAUT) offers a superior technique to conventional methods and is widely used in the construction, pipeline and power generation industries by non-destructive testing/examination (NDT/NDE) experts like Industrial Inspection & Analysis (IIA).

From Medicine to Industry
Industrial ultrasonic applications date back to the early 1950s, when conventional UT techniques were used to determine structural integrity and operational readiness in a variety of components. Defects such as cracks, buried and near-surface welding flaws, minimum wall thickness, degraded material properties, and other anomalies affecting structural integrity all have been evaluated using conventional ultrasonic techniques.

In the 1960s, ultrasonic phased array systems arrived on the scene, thanks to the development of transducers with multiple elements allowing for control of ultrasonic beams. From a commercial perspective, the first phased array systems for use in medical diagnostic applications appeared in the mid-1970s. In the decades that followed, industrial applications evolved as associated technologies were rapidly developed that made ultrasonic testing more reliable, effective and faster than many other methods, such as radiographic (X-ray) inspection (RT) and conventional UT.

How Does Phased Array Ultrasonic Testing Work?
Phased array ultrasonic testing, or PAUT, is an advanced method of ultrasonic testing that is used to determine component quality and detect flaws in manufactured materials, such as welds and base materials.

PAUT uses multiple element probes and electronic time delays to generate sweeping beams. The delays are programmed to generate beams at a specific depth or angle in relation to a target. PAUT can be deployed manually by a technician or automated.

Ultrasonic testing starts with a transducer that converts electrical energy from a generator into sound waves. (With phased array, the transducer is a piezoelectric crystal.) When placed in contact with the weld or other test material, the transducer generates high-frequency sound waves that travel through the item and reflect back. Variations in wave reflections are then analyzed to detect and size cracks, flaws and other defects.

While conventional UT uses a single transducer for testing, phased array UT uses multiple transducers. This allows the technician or computer to direct a series of waves to sweep through the material being tested and provide a more accurate picture of the internal structure. To illustrate the difference between conventional UT and PAUT, imagine sitting in a dark room with a laser pointer and a flashlight. The laser pointer represents conventional UT, while the flashlight represents PAUT.

PAUT Applications & Benefits
Ideal for non-invasive weld examinations, PAUT can be used to detect internal flaws, defects, wall thinning, cracks, voids and pits caused by corrosion in the following types of equipment:

• Storage Tanks & Pressure Vessels
• Small Metal Components (Bolts, Shafts, Pins, Rivets)
• Piping
• Heat Exchangers & Boilers
• Turbine Blades

Minimally invasive and highly flexible, PAUT offers a number of benefits compared to UT and other conventional non-destructive testing methods:

• SAFETY: PAUT is completely safe to use. It requires no protective equipment, safety measures or barricading/exclusion zones required with radiography (X-ray).
• SPEED: PAUT’s portability and ease of use translates to faster testing and, often, cost savings. One comparison found that advanced phased array could scan 10-20 welds per hour, compared to 6-10 for radiography (RT) and 4-6 for manual/conventional UT.
• IMPROVED RECORDKEEPING: PAUT provides a permanent digital record. This means data can be captured, stored and referenced at a later date to aid in auditing, as well as flaw monitoring and maintenance planning.
• BETTER FLAW DETECTION: Because the sound waves can be aimed at different angles, PAUT allows for more complete coverage, including the depth and height of defects, even in complex geometries. Automated PAUT probes can be mounted on robotic crawlers to inspect large, difficult-to-access areas.

Limitations of Phased Array UT
While its benefits are undeniable, PAUT is not the ideal testing method for all occasions. The limitations of PAUT should be taken into account when evaluating test methods.

For example, PAUT may be less reliable than other methods in detecting defects that are very close to the surface. Techniques such as eddy current testing, magnetic particle, dye penetrants and visual testing are typical NDE options for identifying surface cracks and flaws.

PAUT is a more advanced method than conventional ultrasonic testing, with more complex equipment. It is therefore critical to have a trained professional perform PAUT testing to reap the full rewards of the PAUT approach.

Case Study: IIA’s PAUT Drives Change in Railroad Industry
North America’s largest tank car manufacturer, servicer and railway equipment leasing company partnered with IIA to vastly improve railcar inspections and testing data collection.

Prior to hiring IIA, this prominent railcar company inspected tank cars using an antiquated, but code-compliant, manual testing process. To complicate matters further, management had growing concerns that their subcontractor was skipping steps in the manual testing process.

In an effort to update and improve the inspection process and mitigate significant risk, the tank car company partnered with IIA on a blind study that compared automated ultrasonic testing versus manual ultrasonic testing techniques. A Level III NDT Technician from IIA performed three tests — Phased Array Ultrasonic Testing (PAUT), Time of Flight Diffraction (TOFD), and manual ultrasonic testing — on artificially flawed girth seam specimens specially made for the study.

In the end, the TOFD and PAUT results proved exceptional, while the manual test was only 50% successful. Based upon these findings, the tank car company abandoned their previous manual testing process and implemented an automated ultrasonic process to inspect rail car welds. Doing so created a substantial advantage in the safety of in-service tank cars and improved the quality and consistency of the testing process to drastically reduce risk.

IIA also provided advanced NDE testing training to employees of the tank car company so the customer could bring all automated ultrasonic testing in-house. The switch from manual to automated ultrasonic testing proved to be a game-changer for this company and a catalyst for change in the entire industry.

IIA: Your Partner for PAUT
As this tank car company discovered, IIA’s advanced NDE experience is unrivaled. Clients in an array of industries trust IIA for both non-destructive and destructive methods to ensure that welds meet all applicable testing criteria.

As a longstanding leader in NDT, IIA’s history includes extensive research into the applications of phased array ultrasonic for components not typically considered ideal configurations. This research, and extensive field experience, led IIA experts to develop a proprietary PAUT system known as Phased Array Sectorial Scanning (PASS®). The PASS® inspection technique allows for highly accurate testing of complex valves and pipe elbows — without disassembly.

As a full-service provider, IIA also offers NDT training, welding engineering, and complete weld procedure and welder qualification services.

In conclusion, phased array ultrasonic testing offers a faster, simpler, more accurate and less costly alternative for weld inspections. When you partner with a PAUT leader like IIA, you’ll gain confidence in the integrity of your welds and minimize potential risks, delays and expense.