What is Angle Beam Testing?

Have you always wondered what quality inspectors mean when they talk about angle beam testing?

While most ultrasonic testing uses straight beam testing because the anticipated flaw is parallel to the surface, some situations require the use of a testing device that can identify flaws that are perpendicular to the surface of the test sample. For such cases, an angle beam is often very effective. Hence, an angle beam transducer is often required to carry out these tests.

In this post we will give you all the information you require to choose the correct angle beam transducers including its working principle, applications, and their differences from straight beam transducers.

So, if you are ready, let’s dive in. 

I. What is Angle Beam Testing?

Angle beam testing requires the use of angle beam transducers which use the refraction principle and boundary point mode conversion to create shear waves to identify flaws in sample objects. These angle beam transducers like all ultrasonic testing devices convert only detect ultrasonic signals which are frequencies that fall between 1 – 10 MHz. Sometimes, they have transducer wedges that are separate from the main housing. However, they come pre-fitted into the main housing in most cases. 

Unlike straight beams that are not effective for detecting perpendicular-to-surface flaws, angle beam transducers are precise and accurate at measuring flaws that are mostly vertical and perpendicular to the surface of the test sample. Also, a beam transducer is very accurate at measuring flaws in welding operations when considering the flaws orientation, the weld geometry, and the weld crown needing examination with the beam projected at an angle from the weld side. 

Angle beam testing is often the most preferred non-destructive testing method in ultrasonic flaw detection. 

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II. What is Straight Beam Ultrasonic Testing?

For straight beam testing, transducers often project longitudinal waves that are parallel to the surface of the sample under examination and are often used to identify flaws in the same parallel plane. These flaws can include porosity, cracks, and delamination. 

Also, the transducer type can be contact, immersion, dual, or delay line transducers which can all generate longitudinal waves only. However, they can also identify flaws in components like bars, castings, forgings, test plates, and bolts which often have flaws parallel to the test plane. Moreover, they employ the principle of ultrasonic wave travel through a medium which is simply the continuous movement of ultrasonic sound waves until it encounters a barrier like cracks or voids within a medium.

III. What is the Difference between Straight Beam and Angle Beam Transducer?

While they both share similarities like overall testing principle and signal generation and conversion for flaw detection, straight beam, and angle beam transducers both have several differences that makes them unique. 

Firstly, the type of flaws detected is different for these transducers. While straight beam transducers detect flaws that are parallel to the test sample’s surface, angle beam transducers are very effective for defects that are either at an angle or vertical to the surface of the test sample. 

Again, their applications which are based on the type of flaw they detect are also different. While straight beam transducers are generally the best for defects like delamination in components like plates and hanger pins, angle beam transducers are accurate for pipes and tubing where flaws are at an angle to the test material surface. 

Additionally, straight beam transducers project their waves perpendicular to the test sample’s surface, but they move along the longitudinal side of the object to detect flaws. On the contrary, angle beam transducers often project their waves at angle to the object’s surface to detect any flaw that may not be parallel to the object’s surface. 

IV. What are Features and Benefits of Angle Beam Testing?

The primary objective of angle beam testing is to ascertain the integrity and quality of welds and sample objects using angle beam transducers and their accompanying accessories like wedges. However, they feature easy back and forth scanning within a short approach distance. But essentially their main feature is the piezoelectric element which is usually a single element that can both generate and receive ultrasonic signals with this single element. Additionally, they feature a wedge that both be inbuilt or separately built from the main housing for easy assemblage. Also, the wave form is often a refracted shear wave to efficiently detect flaws which are perpendicular to the test sample’s surface. Needless to say, that with all these features angle beam testing provides some unique advantages over straight beam testing including 

• Improvement of signal-to-noise characteristics 
• Excellent durability with wear resistance
• Very accurate for high temperature use cases with wedges that are very resistant to the effects of high temperature. 
• Customizable wedges with possibilities for detachable options for and can create non-standard refracted angles
• Wedges and integral designs are available with standard refracted angles in aluminum

V. What are Applications of Angle Beam?

With the projection of angle beam to detect perpendicular flaws, angle beam transducers have specific use cases that make them unique especially for certain applications. These applications include:

• Flaw sizing and detection – For metals used as production raw materials like ingots, plates, bars, and tubes, the presence of flaws in these components automatically introduces defects into the final product. To avoid such cases of primary product defect, angle beam testing is often an effective test to ascertain the presence of perpendicular-to-surface flaws, 
• Inspection of welds – For pipes, forging, tubes, and castings, including machined and structural components, inspecting for weld defects can be difficult without angle beam testing. Angle beam transducers are very effective for identifying defects like weld cracks in these components since these flaws often occur perpendicular to the surface. Angle beam transducers are especially useful for confirming the depth of the weld like in gear welds where laser welding has been employed. 

• Composite material testing – Angle beam testing is not limited to testing metals alone, but composite materials and fiber-based materials can also be tested using angle beam transducers. Defects like delamination.

VI. How to Choose Your Angle Beam Transducer?

In numerous cases, inspectors use various standard codes to choose the angle beam transducer that they intend to use for certain quality assessment inspections. Nevertheless, some critical parameters determine the choice of a suitable angle beam transducer for any given inspection. These parameters include the frequency of the transducer, the beam angle, and the element size. These three parameters are key to choosing the right parameter and they are highlighted below along with other essential factors.

• Frequency – The importance of a transducer frequency is based on its effects on the flaw resolution and penetration. The reason is because the distance the sound wave traveling in a given material decreases as the frequency increases. However, the resolution of small discontinuities often improves. Also, the distance traveled by the sound wave increases as frequency decreases. Yet, the least detectable flaw size becomes bigger.

• Angle – The geometry of the sample object under examination usually determines optimal beam angle of the test sample as well as the anticipated flaws that the transducer is set to identify. 

• Size – In the same vein, larger element sizes often decrease inspection duration when the coverage area increases, but for small discontinuities the reflected echo amplitude will decrease and vice versa. 

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Conclusion

To conclude, angle beam testing is a unique testing method whenever ultrasonic non-destructive testing is involved. The difference between straight beam testing and angle beam testing makes it even more preferable in ultrasonic testing as it ensures the capture and identification of angular or perpendicular flaws in sample objects. Nonetheless, understanding its working principle is important in order to ascertain its suitability for your inspection use. Again, knowing the parameters to consider when choosing the angle beam transducer is equally critical in choosing the right model. Ultimately, things like frequency, element size, and the angle of the wave generated can significantly affect the accuracy of the results you get.