What are Advantages and Limitations of Ultrasonic Testing?

Ultrasonic Testing

Introduction

Ultrasonic testing is an important technique that helps check for any fault in an object or material. This post will highlight the advantages and disadvantages of ultrasonic testing in depth. UT is a method of non-destructive testing based on the transmission of ultrasonic waves in the object tested.

In most ultrasonic testing applications, short waves ranging from 0.1-15 MHz transmit into the materials to detect internal faults.

One typical example is measuring ultrasonic thickness to test the object’s thickness, such as checking the pipework corrosion.

NDT-KITS (Honesdom international HK limited) is a high-tech company where we focus on the research, development, and manufacturing of ultrasonic equipment as well as ultrasonic probes.

1. What is Ultrasonic Testing? 

Ultrasonic testing (UT) is a non-destructive test technique used to utilize sound waves to identify cracks and malfunctioning in materials and parts. Also, UT is used to measure the thickness of a material, such as measuring a pipe’s wall thickness.

Since the technique has higher power potential than non-destructive test methods, ultrasonic testing produces well-defined images and shows the properties deeper than surface-level than any other method.

2. Why is Ultrasonic Testing Important?

This technique is also known as a comparative method. Some analog-based ultrasonic testing devices exist, but recent devices incorporate digital signal processing to enhance stability and accuracy.

A non-destructive testing technique, ultrasonic testing is best for detecting errors and defects without destroying the material or object being tested. Repetitive ultrasonic checks can detect any corrosion or growth of unidentified errors, preventing the failure of a part of the whole asset. Ultrasonic testing is used in many industrial applications such as automotive, medical, aerospace, metallurgy, construction, and manufacturing.

3. How does Ultrasonic Testing Work?

In this technique, an ultrasound transducer, especially phased array transducer attached to a detecting gadget is passed over the material or object being checked. The transducer is then detached from the test object using water or couplants such as oil as immersion testing.

When an electric current passes, the transducer vibrates at a given frequency, producing an ultrasonic sound wave with 40 kHz. The sound waves produced transmit in a specific direction. In the case of any object on the route, an echo is generated then the waves bounce back to the transducer. The device converts the echo into an electrical signal.

However, when the test is done using Electromagnetic Acoustic Transducer (EMA), couplants are not needed.

4. What is the Basic Principle of Ultrasonic Testing?

Ultrasonic Testing uses HF sound energy to carry out tests and make measurements. Ultrasonic testing (UT) is used for flaw check, material characterization, and dimensional measurements.

A typical ultrasonic testing detection system has a number of functional elements, such as the transducer, receiver, and display devices. A receiver is an electronic device that produces electrical pulses at high voltage. On the other hand, a transducer is driven by a pulser to generate HF ultrasonic energy. The sound energy is generated and moves through the materials in the waveform. all the process need to be calibrated by ultrasonic calibration block.

 In case of a disconnection, maybe due to cracks in the wave route, some energy is reflected from the defective surface. Then, the transducer converts the reflected wave signal into an electrical signal and is shown on a screen. 

There are two methods used in receiving the ultrasound waveform. They include reflection and attenuation methods.

Reflection method

The transducer sends and receives pulsed waves in reflection mode as the sound is sent back to the device. The reflected ultrasound is generated from a link such as an imperfection inside the object or from the back wall.

In this method, the detecting device displays the results in the form of signals with a maximum displacement representing the strength of the reflection and the displacement representing the reflection arrival time.

Attenuation method

The attenuation method is also known as through-transmission mode, and a transmitter directs ultrasound through a single surface. Then, a single receiver senses the amount that reaches it on a different surface after moving through the medium.

Flaws or any other conditions in the vacuum between the receiver and the transmitter minimize the volume of sound transmitted, hence showing their existence. When a couplant is used, it increases the accuracy of the process by reducing the ultrasonic wave energy loss due to the space between the surfaces.

5. What are Advantages and Disadvantages of Ultrasonic Testing?

Have you considered the advantages and limitations of ultrasonic testing? What are they? Here are some of them listed below:

Advantages of Ultrasonic Testing

  • High sensitivity, allowing identification of very small flaws
  • Only one service needs to be accessible
  • More accurate than non-destructive techniques in determining the thicknesses of parallel surfaces and how deep internal flaws are.
  • High penetrating power for easy detection of flaws in deep parts
  •  Has the ability to estimate the shape, size, orientation, and nature of defects.
  •  Has no adverse effects on equipment and materials used 
  • Ability to estimate the structure of compound constituents with different acoustic features
  • Non-hazardous to operators or any nearby personnel
  • Best of portable or automated activities
  •  Immediate results. Hence decisions can be made on the spot      

Disadvantages of Ultrasonic Testing 

  • Parts that are irregular in shape, rough, very thin or small, or not uniform are not easy to inspect
  • The surface of the test  material must be prepared by removing loose scale, cleaning, paint, etc., but paint well bonded to the surface should not be removed
  • Inspected objects or materials should be water-resistant if you use water-based couplants that lack rust inhibitors. Antifreeze fluids with inhibitors are best
  • Manual operations should be carried with a skilled technician’s attention. The transducers alert to both tolerable anomalies of specimens (termed “noise”), the normal structure of some objects, and serious flaws that could compromise the integrity of the specimen. These signals should be inspected by experienced technicians able to follow up with other testing methods such as non-destructive methods
  •  Wide technical knowledge is a must for the creation of inspection processes
  •  Couplants are used to offer effective transmission of ultrasonic wave energy between the parts being inspected and the transducers unless when using a non-contact method. Non-contact methods include Electro-Magnetic Acoustic Transducers and Laser.

Conclusion

Having read through this post, you must have realized that ultrasonic testing is very important in sound transmission. It is an essential technique that should be carried out by skilled personnel for its effectiveness to be felt. Therefore, you should be careful when using the method to avoid adding more problems to the material instead of reducing the flaws. 

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