Published on 25-Apr-2024

Ultrasonic Testing Procedure: Explained Step-By-Step

Ultrasonic Testing Procedure: Explained Step-By-Step

Table Of Content

What is Ultrasonic Testing?

An Ultrasonic Testing Machine under operation

Ultrasonic testing is a versatile and indispensable tool in NDT, enabling the detection of a broad spectrum of flaws, including cracks, voids, and inclusions, all while being non-invasive and highly accurate.

Ultrasonic Testing Schematic

Ultrasonic Testing detects internal defects using high-frequency sound waves that are non-audible to human ears. It can be used to detect flaws inside any solid material.

What is an Ultrasonic Testing Procedure?

The procedure for Ultrasonic Testing entails the generation of high-frequency sound waves using a transducer, which is then directed into the material under examination.

As these sound waves propagate through the material, they encounter boundaries between different media or internal flaws, subsequently reflecting the transducer.

Expert technicians analyse the time it takes for the sound waves to return and their amplitude, allowing for precise determination of the size, location, and nature of any discontinuities within the material.

Important Terms in Ultrasonic Testing

Some Important terms in Ultrasonic Testing, that are vital to understanding UT Testing procedures include:


The transducer emits ultrasonic waves and receives echoes. It is a pivotal component of ultrasonic testing equipment.


A coupling medium is typically a gel or liquid, applied to the transducer to facilitate effective sound wave transmission between the transducer and the material under inspection in the ultrasonic examination.


When an ultrasonic wave encounters a boundary or flaw within the material, it reflects back to the transducer, creating an echo. The time and amplitude of these echoes are used to assess the material's condition.


Wavelength is the distance between two successive points in a sound wave. Wavelength is inversely proportional to frequency, i.e. higher-frequency waves have shorter wavelengths.


Ultrasonic waves are generated at specific frequencies. The choice of frequency depends on the material's thickness and the nature of the flaw being inspected in ultrasonic testing work.


Velocity refers to the speed at which ultrasonic waves travel through a material. Velocity is a critical parameter in calculating the material's thickness.

Ultrasonic Testing is a crucial NDT method for inspecting materials and structures. Proper equipment, adherence to standardised procedures, and comprehension of key terminology are essential for achieving accurate and reliable results in UT.

A well-defined procedure ensures consistency, safety, standardisation, and quality assurance in ultrasonic testing, ultrasonic examination, and ultrasonic NDT testing.

Basic Requirements for Ultrasonic Testing

The basic requirements for performing NDT Ultrasonic Inspections include:

Ultrasonic Testing Equipment:

Essential equipment includes an ultrasonic flaw detector, transducers (or probes), and a couplant.

The flaw detector generates and receives ultrasonic waves, while transducers emit and receive the waves, and the couplant facilitates sound wave transmission.

Schematic of the movement of an Ultrasonic Wave

Calibration Standards:

Calibration standards typically consist of known defects with precisely measured dimensions, serving as reference points for equipment performance evaluation in Ultrasonic Testing NDT.

Surface Preparation:

Thorough surface preparation is vital to ensure accurate results. The material's surface should be clean and free from contaminants that could hinder sound wave transmission.

Training and Certification:

Properly qualified personnel are essential for conducting ultrasonic testing. Technicians must undergo training and certification to understand the principles, techniques, and best practices of UT examination and ultrasonic NDT testing.

Need for Ultrasonic Testing Procedures

Efficient industrial operations require a standard operating procedure. When it comes to special techniques like Non-destructive testing (NDT), it is essential to have approved procedures, often obtained in reference from the international standards.

A few of the global inspection standards for Ultrasonic Testing include:

  • ASME Boiler & Pressure Vessel Code – Section V
  • BS EN ISO 17640 (British & ISO Standard)
  • SAE AMS 2630, SAE AMS 2632 – (Aero Space Standards)

A well-defined procedure in ultrasonic testing provides some significant benefits, some of which include:


Procedures ensure consistent testing, minimising human error and reducing variability in results.


Proper procedures incorporate safety guidelines to protect operators and equipment during ultrasonic examination.


Following established procedures helps maintain uniformity and compliance with industry standards and regulations.

Quality Assurance:

Procedures enable the accurate detection and documentation of flaws, ensuring the quality and reliability of materials and structures.


Procedures are valuable training tools for technicians, guiding them in understanding and implementing best practices in ultrasonic NDT Testing and ultrasonic examination.

Formulating a Procedure for Ultrasonic Testing

A well defined Ultrasonic Testing procedure must include the following:

1. Scope: This section delineates the range of the procedure, specifying the materials, types of weld joints, and techniques covered.

2. References: It includes citations of international or local standards that the procedure adheres to.

3. General Requirements: This part outlines the fundamental prerequisites, including:

  • Personal qualifications,
  • Equipment capacity requirements,
  • Search unit size and frequency (Probe),
  • Couplant specifications, and
  • Calibration and reference standards.

4. Inspection Procedure: Here, the step-by-step process of conducting the inspection is detailed.

5. Evaluation of Indications: This section discusses the assessment of indications detected during the inspection.

6. Acceptance Criteria: It sets forth the criteria for determining whether the inspected material meets the required standards.

7. Documentation & Report Format: This component outlines the format and content requirements for documenting inspection results in a report.

Requirements of an Ultrasonic Examination Procedure

The procedure should encompass all essential variables mentioned in relevant standards, such as those outlined in ASME Section V Article 4.

Surface Preparation in Ultrasonic Testing Methods

Effective surface preparation is a fundamental aspect of ultrasonic testing NDT, ensuring reliable results from the ultrasonic examination process. Key factors in surface preparation for ultrasonic applications include:

Clean Surface for NDT:

A clean surface is essential for accurate ultrasonic testing NDT. The test subject should be free from contaminants such as dirt, oil, rust, and paint.

These foreign substances can interfere with the transmission and reception of ultrasonic waves, affecting the reliability of the non-destructive testing procedure.

Surface Smoothness in Ultrasonic Examination:

The surface should ideally be smooth and devoid of rough or irregular areas that might scatter or attenuate sound waves.

This consideration becomes particularly critical when inspecting materials with complex geometries, underlining its significance in ultrasonic examination work.

Optimal Couplant Application:

Couplant, a specialised gel or liquid, is employed to enhance the transmission of ultrasonic waves between the transducer and the material.

Optimal Couplant Application

Proper coupling application is a fundamental practice that ensures efficient contact and sound wave transmission in NDT ultrasonic testing and ultrasonic examination.

Addressing Surface Irregularities:

Surface irregularities, such as pitting or corrosion, should be assessed individually, as they can influence the interpretation of ultrasonic results.

The use of calibration standards with known defects can facilitate the evaluation of these irregularities, which is particularly important when working with various materials and flaw sizes in NDT testing.

Equipment Required for Ultrasonic Testing Procedures

Search Units in Ultrasonic Testing Inspection:

Search units, commonly referred to as transducers or probes, serve as the heart of ultrasonic testing equipment in ultrasonic testing inspection. They emit ultrasonic waves into the material and receive echoes in return.

These essential components come in various types, differing in frequency, size, and shape to cater to specific non-destructive testing applications, including ultrasonic testing NDT and ultrasonic examination.

Screen Height Linearity in NDT Ultrasonic Testing:

Screen height linearity is a critical parameter in the ultrasonic flaw detector. It ensures the instrument accurately displays the depth of flaws, a foundational element in ultrasonic NDT.

A reliable flaw detector with excellent screen height linearity provides precise depth measurements, an essential aspect of NDT ultrasonic testing.

Amplitude Control in NDT Testing:

Linguistics of amplitude control refers to the precise adjustment of ultrasonic signal strength and echoes during NDT testing.

This control is a vital consideration, as it allows for detecting subtle indications by amplifying or reducing signal amplitudes.

It is especially pertinent when working with various materials and flaw sizes in NDT ultrasonic testing techniques.

Couplant Use in Ultrasonic NDT Testing:

Couplant is an indispensable element of Ultrasonic Testing procedures, ensuring proper contact between the transducer and the material.

The selection of a couplant depends on the specific application and the material under inspection in NDT ultrasonic testing and ultrasonic examination. Typical choices include gels, oils, and water-based solutions.

Read Now - A Comprehensive Guide on Ultrasonic Testing Equipments

Step-by-Step NDT Ultrasonic Testing Procedure

Steps Involved in UT Testing Procedure

  • Equipment Setup:

Assemble and calibrate the ultrasonic testing equipment, including the flaw detector and appropriate transducer (probe).

Ultrasonic Flaw Detector

  • Surface Preparation:

Clean the material's surface, ensuring it is smooth and free from contaminants that could interfere with sound wave transmission.

  • Couplant Application:

Apply a suitable couplant to the transducer for efficient sound wave transmission.

  • Probe Placement:

Position the transducer on the material's surface, ensuring good contact for sound wave transmission.

  • Sound Wave Emission:

Emit ultrasonic waves into the material through the transducer, which propagates and encounters boundaries or internal flaws.

  • Echo Reception:

The transducer receives echoes generated when ultrasonic waves encounter boundaries or flaws within the material.

  • Data Analysis:

Analyse time-of-flight and amplitude of echoes to determine the size, location, and nature of defects.

  • Calibration and Reference Standards:

Use calibration standards for equipment verification and reference standards for surface irregularity assessment.

  • Adjusting Parameters:

Optimise NDT equipment settings, including amplitude control, based on material thickness and defect type.

  • Recording and Documentation:

Record inspection results and relevant data for documentation.

  • Interpretation and Evaluation:

Interpret data to assess the material or structure's condition based on established criteria and standards.

  • Reporting:

Generate a detailed report summarizing inspection findings, including defect location, size, and depth.

  • Follow-up Actions:

Based on inspection results, take appropriate follow-up actions, such as repairs, further testing, or monitoring.

Adhering to a standardised procedure is essential to ensure the accuracy and reliability of the inspection process.

Ultrasonic Testing Procedures- An Enabler of Longevity

The procedure for performing Ultrasonic Testing is a meticulously orchestrated process that relies on advanced technology, precise techniques, and the expertise of trained professionals.

From equipment setup to the interpretation of results, each step plays a pivotal role in unveiling the hidden secrets of materials and structures.

As a critical component of the broader field of non-destructive testing (NDT), ultrasonic testing inspection exemplifies the precision and rigour found in NDT techniques, ultimately contributing to the integrity and longevity of structures and materials in a myriad of industries.

Key Takeaways

  • Ultrasonic Testing is a non-destructive testing method that uses high-frequency sound waves to inspect materials for hidden flaws without causing damage.
  • The process involves transmitting ultrasonic waves into the material, receiving echoes or reflections, and analysing the data to detect and characterise defects such as cracks, voids, and thickness variations.


1. Why is a well-defined Ultrasonic Testing procedure important?

A: A well-defined procedure ensures consistency, safety, and quality assurance in ultrasonic testing by providing clear guidelines and minimizing errors.

2. What are the key components of an Ultrasonic Testing procedure?

A: The key components include scope, references, general requirements, inspection procedures, evaluation of indications, acceptance criteria, and documentation/reporting formats.

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Application Notes