Time of Flight Diffraction (TOFD) testing is an advanced ultrasonic non-destructive testing (NDT) technique used to inspect and evaluate the integrity of materials, primarily weld defects, flaws, and cracks. 

TOFD works by sending ultrasonic waves into the material being tested from a transmitting transducer. These waves travel through the material until they encounter a change in the material’s structure, such as a crack, void, or weld defect. When the ultrasonic waves interact with these changes, they produce diffraction, which is detected by the receiving transducer. 

TOFD offers the highest probability of detection for UT methods and is a sensitive and accurate location and sizing tool of defects due to the measurement of time-of-flight rather than amplitude from diffraction of crack tips. 

TOFD is a specific ultrasonic testing technique that excels in the detection and characterization of planar defects like weld flaws and cracks. Conventional UT methods are more versatile and can be applied to a broader range of testing scenarios, including thickness measurements and general flaw detection. The choice between TOFD and conventional UT depends on the specific requirements of the inspection and the types of flaws one needs to detect and characterize. 

While Time of Flight Diffraction (TOFD) is commonly used for weld inspection, it is not limited to this application. TOFD can be used for a wide range of non-destructive testing (NDT) and inspection purposes in addition to weld inspection, including corrosion and defect detection. Some of the other industries where TOFD can be applied include piping inspection, pressure vessel inspection, aerospace, power generation, structural inspection, manufacturing and nuclear. 

While TOFD is versatile, it’s essential to choose the most appropriate non-destructive testing technique for a specific application, considering factors such as the type of material, the nature of the defects of interest, and the available equipment. Speak to an Ionix expert to find out which technique will be most suitable for your application: contact@ionix.at 

Our inspection probes are compatible with all standard ultrasonic thickness gauges and flaw detectors that can display an A-scan and B-scan. See international standards ISO 16282 for more information on equipment selection.  

The Ionix probes have Lemo 00 type connectors as standard which can be used with any compatible cable to provide connections to your unit. 

Time of Flight Diffraction (TOFD) uses specialized wedges, to generate and receive longitudinal ultrasonic waves for flaw detection and sizing. These TOFD wedges come in various angles and configurations, and the choice of wedge size is important for optimizing the inspection process. Here’s what different size TOFD wedges are and what they mean: 

70 deg, 6 MHz probe – The higher frequency improves the resolution and high nominal probe angle helps to reduce the dead zone near the surface. Recommended for wall thickness from 4 to 25 mm. 

60 deg, 5 MHz probe – Balancing detection resolution and depth of penetration across the temperature range. The nominal probe angle of 60° make it suitable for wall thickness from 12 mm to 30 mm. 

50 deg, 5 MHz probe – The lowest probe angle makes it suitable for thicker parts. 

HotSense TOFD is not only suited for high-temperature applications. It exhibits remarkable sensitivity in detecting weld defects throughout a wide temperature range, from -55 to +350 °C (-67 to +662 °F). This means that inspectors can readily employ TOFD inspections at regular, ambient temperatures, and through the wide operating temperature window without any compromise in the quality of the readings. Whether examining materials under extreme heat or typical environmental conditions, TOFD consistently delivers accurate and high-quality results. 

All probes provide very precise thickness measurements on many materials, including metals, glass, and ceramics.  

TOFD is a pitch-catch technique, using two probes arranged in a pair. One probe acts as the transmitter, and the other as the receiver. These two probes work in tandem to send and receive ultrasonic waves, allowing for accurate time-of-flight measurements and the detection of flaws within the material being inspected. 

Although two are needed you can purchase individual probes if you need a replacement. 

The wedge angle is typically defined and calibrated at a specific reference temperature. The reference temperature for HotSense TOFD is the refracted angle in carbon steel at 200 degrees Celsius (392 degrees Fahrenheit).  

Integrated wedges can be used in TOFD setups for several important reasons such as simplicity, alignment, consistency and compactness. 

HotSense TOFD integrates the wedges with the transducer, which requires a kit of parts to cover the most common inspection parameters, but the integrated wedges offer many advantages including increased sensitivity, simplicity and reduction in velocity drift when operating across the wide temperature range. It’s important to choose the right type of integrated wedge for the specific application and material being inspected, get in contact with an Ionix expert to find out what wedge you need: contact@ionix.at 

For more information and guidance, see our blog How does temperature affect my angled wedge inspection?  – Ionix Advanced Technologies