Published on 23-Apr-2024

A Comprehensive Overview on Ultrasonic Testing

A Comprehensive Overview on Ultrasonic Testing

Sources - Wikipedia

Table of Content

Did you know that the ultrasonic testing principle has applications beyond the medical field? Indeed, its significance extends to various industries. Ultrasonic Testing inspection is a widely used NDT method that plays a crucial role in various industries, such as manufacturing, construction, aerospace, and oil and gas, focusing on the Ultrasonic Flaw Detector and transducers, and delving into the procedure to give readers a clear understanding of its significance and applications.

What is Ultrasonic Testing?

Ultrasonic Testing Performance

The ultrasonic testing principle serves as an NDT procedure extensively employed in contemporary industries. Many ultrasonic testing advantages are highly beneficial approaches for detecting material discontinuities. Just like in healthcare and underwater navigation, ultrasonic testing plays a vital role in Ultrasonic Testing Equipment, ultrasonic sound testing, ultrasonic metal testing, ultrasonic inspection, and detecting anomalies, including those identified through the Rebound Hammer Test.

To inspect materials and identify faults or characterize the material, high-frequency noises, commonly known as ultrasonic waves, are sent through the object or material. In typical ultrasonic tests, short ultrasonic pulse waves with center frequencies ranging from 0.1 to 15 MHz, occasionally up to 50 MHz, are delivered into materials for characterization and internal fault identification. For instance, Ultrasonic Thickness Measurement is a frequently encountered application that checks the thickness of the test subject, such as monitoring Pipeline Corrosion.

Why is the Ultrasonic Test Important?

Ultrasonic Test Important

The ultrasonic test detects material discontinuities by using high-frequency sound waves that propagate through the material. There are several advantages of ultrasonic testing, that help with the sound portion. As it encounters a material with a different acoustical impedance, some of the sounds will reflect back. The sending device detects this reflected sound and displays it on the screen as an indication. By knowing the sound's velocity through the material and the time of transit, the NDT Technician can calculate the distance to the indicated material with a change in acoustic impedance.

To conduct Ultrasonic Testing, a technician introduces sound waves into the object through a piezoelectric crystal transducer. This crystal's role is to convert electrical current into sound waves. The two most common types of sound waves used in this process are compression waves, also known as longitudinal or straight beam waves, and shear waves, also known as transverse or angle beam waves. The ultrasonic testing principle is of utmost importance as it finds extensive applications.

NDT Technician

One such example is Ultrasonic Thickness Measurement, which is used to determine the thickness of an object, such as in assessing piping corrosion. Being an NDT technology, ultrasonic testing excels at detecting errors and flaws without causing any material damage using various approaches like ultrasonic sound tests and ultrasonic inspection. By regularly employing the ultrasonic testing principle to check for defects or corrosion growth, potential issues can be avoided. Early detection of damage can prevent machine parts, components, or entire structures from failing. Industries such as construction, aerospace, medical, automotive, metallurgy, and manufacturing widely embrace ultrasonic testing. 

What are the Basic Principles of Ultrasonic Testing?

A sound wave is sent into a test substance by a probe, as depicted on the left. There are two signs, one from the probe's first pulse and the other from the back wall echo. As illustrated in the right-hand figure: A fault produces the third indication while also lowering the amplitude of the back wall indicator. The ratio D/Ep determines the depth of the flaw.

Ultrasonic Testing Principle

Ultrasonic Testing is based on a process known as ultrasonography, which is the transmission and reflection of sound waves. Ultrasonic waves are sent through the substance to be evaluated and then reflected into a receiver in this procedure. This receiver then processes the signals, which creates a three-dimensional representation of the materials, allowing any flaws to be spotted. The ultrasonic waveform is received in one of two ways. Reflection and attenuation techniques are the two Types of Ultrasonic Testing.

1. Reflection Method

In the reflection method, the transducer accomplishes both the sending and receiving of pulsed waves (pulse-echo mode), as the "sound" is reflected back to the instrument. Reflected ultrasound is generated at interfaces, such as the object's back wall or a flaw within the object. The diagnostic machine displays these data as a signal, with an amplitude representing the reflection's strength and distance representing the reflection's arrival time.

2. Attenuation Method

In the attenuation method, a transmitter delivers ultrasound through one surface while a separate receiver measures the quantity of sound reaching another surface after passing through the medium. Imperfections or other factors in the area between the transmitter and receiver cause less sound to be transmitted, indicating their presence. The use of a coupling medium improves the process efficiency by reducing ultrasonic wave energy losses due to the separation between the surfaces.

What is the Ultrasonic Testing Procedure?

Ultrasonic testing uses high-frequency sound energy to perform tests and measurements. It is employed to detect flaws and characterize materials using all major Ultrasonic Testing Equipment. A conventional ultrasonic testing and detection system consists of three functional components: the Ultrasonic Transducer, receiver, and display devices.

Ultrasonic Testing Procedure

When using an Electromagnetic Acoustic Transducer (EMAT) for ultrasonic testing, couplant is not required. In the event of a discontinuity, some energy reflects from the flawed surface, which may result from cracks in the wave path. The Ultrasonic Transducer converts the reflected wave signal into an electrical signal, displaying it on a screen. The procedure involves several essential steps to ensure accurate and reliable results. Here are the various steps.

1. Surface Preparation

Before conducting the NDT UT, the test surface must be adequately prepared. It involves cleaning the surface to remove any dirt, oil, or debris that could interfere with the inspection. A clean surface ensures better contact between the transducer and the test material, improving the accuracy of the results.

2. Calibration

Calibrating the UT Equipment is a crucial step to ensuring accurate defect detection. During calibration, the instrument is set to specific parameters, such as sound velocity and gain, using reference samples with known defects or features. This process establishes a baseline for the inspection, allowing the operator to interpret the results accurately.

3. Coupling Media

For contact UT, a coupling medium is used to enhance the transmission of ultrasonic waves between the Ultrasonic Transducer and the test material. Common coupling media include water, oil, or gel, depending on the application and material being inspected. The coupling medium eliminates air gaps that could hinder sound wave transmission, ensuring effective inspection.

4. Transducer Placement

The transducer, which emits and receives ultrasonic waves, is placed on the test surface with the help of the coupling medium. Proper transducer placement is crucial for obtaining reliable data. For contact UT, the transducer is placed directly on the surface, while for immersion UT, the test material is immersed in a liquid couplant.

5. Scanning Techniques

Scanning involves moving the transducer over the test surface in a systematic pattern to cover the entire area of interest. The operator may use different scanning NDT Techniques based on the object's geometry and the type of flaw being sought.

Common scanning techniques include:

Straight Beam Scanning: In straight-beam scanning, the transducer emits sound waves perpendicular to the test surface. This technique is used to detect defects oriented parallel to the surface, such as cracks or delaminations.

Angle Beam Scanning: Angle beam scanning involves tilting the transducer at a specific angle to the surface. This technique is used to detect defects at different depths within the material, making it suitable for Inspecting welds and other components with oblique defects.

Ultrasonic Flaw Detector

6. Data Collection and Analysis

During scanning, the Ultrasonic Flaw Detector captures the data in the form of A-scans, which display the amplitude of the reflected waves over time. The operator analyses the A-scans to identify any indications of defects or irregularities within the test material. Proper analysis and interpretation are crucial for making informed decisions regarding the material's integrity.

Get Complete Information on the Ultrasonic Testing Procedure Here!

7. Reporting

After completing the inspection, a detailed report is generated, documenting the inspection results, any detected flaws, and their locations within the test material. This report serves as a valuable reference for future evaluations and maintenance decisions.