What Is NDT? (With Definition, Uses And Common Benefits)

By Indeed Editorial Team

Published 27 July 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

It is important to preserve the usefulness of equipment, components and materials to avoid a negative impact on the environment. Non-destructive testing (NDT) is a comprehensive way to find discontinuities or flaws in equipment or components to avoid catastrophic failures, follow industry regulations and standards and ensure the safety of assets and personnel. By learning about NDT, you can monitor the integrity of equipment during inspections and meet the relevant standards and specifications of each test. In this article, we answer the question, "What is NDT?", explore its types and look at some of its uses and benefits.

What Is NDT?

Understanding "What is NDT?" can help you maintain the serviceability of critical pieces of equipment and preserve their usefulness. NDT refers to an array of methods for evaluating and collecting information about materials, systems, welds and components in a way that does not permanently modify them. Several industries use NDT, such as oil and gas, aerospace, automotive, chemicals, mining, maritime and power generation.

Because of its non-destructive nature of testing, NDT causes no damage to the material or product being tested. It is possible to make minimal adjustments to existing products without having to produce completely new ones.

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Destructive Testing Vs. Non-Destructive Testing

Destructive testing is a qualitative analysis method which measures the mechanical qualities of a material, such as hardness value, tensile strength, impact toughness and elongation property. NDT is cost-effective and does not harm assets while finding weaknesses. NDT is more efficient than destructive testing for inspections, requiring fewer manual steps. Destructive testing can be more time-consuming and labour-intensive than NDT's simplified methods.

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Common NDT Techniques

Here are some NDT techniques:

Visual testing

Visual testing (VT) involves collecting visual data on the condition of a material. Visual NDT is the observation of a test object, either through the naked eye or through the use of optical instruments, to identify surface anomalies and ensure conformity to specification. It is the simplest method of examining a material or object without modifying it. The visual testing equipment includes magnifying glasses, cameras and video probes. This technique allows fast control of quality at every stage of fabrication and maintenance, facilitating a reduction in repair costs and documentation of observations using measurement tools.

Ultrasonic testing

An ultrasonic test (UT) transmits wave signals into structures and primarily detects erosion and corrosion. The test provides information on the depth, size, nature and orientation of detected defects. In this technique, inspection systems, receivers, transducers and display devices are all part of a multi-functional unit. Ultrasonic testing is sensitive to both surface and subsurface discontinuities with high accuracy and high penetration power that is non-hazardous to nearby equipment and personnel.

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Eddy current testing

An eddy current test (ET) relies on electromagnetic induction and is a non-contact method for inspecting metallic parts. Using alternating current (AC), a coil surrounding the test part gets energised and creates a magnetic field that interacts with the part and generates eddy currents. Various manufacturing and service environments use eddy current testing to inspect thin metals for potential safety or quality issues. It is a reliable and simple inspection technique for detecting near-surface and surface defects in conductive material.

Radiographic testing

A radiographic test (RT) examines a specimen's volume by examining its internal structure through X-rays and gamma-rays. Radiographs of the test specimen show changes in thickness, defects and assembly details to ensure optimum quality. The high dependability of radiographic testing makes it useful for several industries, including power generation, transport, manufacturing, oil and gas, aerospace and automotive. This testing is ideal for verifying internal defects on complex structures and assembled components.

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Magnetic particle inspection

A magnetic particle inspection (MPI) is a surface examination method used to detect linear defects on or near the surface of ferromagnetic materials. It uses a magnetic field to detect irregularities in a target sample. The application of ferrous particles or ferrofluid can detect irregularities in the material by looking for areas where the ferrous materials have accumulated strongly, indicating a defect.

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Liquid penetrant testing

Liquid penetrant testing (LPT) is one of the most common and inexpensive non-destructive testing methods. The method uses capillary action to detect surface-breaking defects even when external forces, such as gravity, acts in opposition. This procedure involves applying a low viscosity liquid to the material being tested. The penetrant liquid seeps into flaws, such as cracks or porosity, prior to developer application, which causes the flaw to be visible. This testing works well with complex geometric shapes and has few material limitations.

Acoustic emission testing

Acoustic emission testing (AE) detects and measures the release of ultrasonic stress waves during rapid redistribution of energy from localised sources in a material. As opposed to conventional ultrasonic testing (UT), which detects very specific defects, acoustic emission testing (AET) discerns signals caused by a material's failure or stress, rather than from an external source. During the manufacturing process, AET can detect defects, such as cracks in pipelines that may go undetected during welding.

Leak testing

Leak testing is a type of non-destructive testing that ensures that fluids and gases do not escape from manufactured parts. The types of leak testing include helium leak, flow monitoring, total submersion, pressure decay and thermography. Tests like this are common in many industries where leaks could occur, including oil and gas, medical, automotive and waterproof electronics.

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Advantages Of NDT

NDT tests are convenient to perform, since they do not require disassembly or interruption of operation. Some advantages of NDT include:

Cost efficiency

Structures in the industrial sector often experience chemical attacks, thermal shocks, weathering and corrosion, which can lead to their rapid deterioration. Industry regulations and safety standards help check such damages. Non-destructive testing is a cost-effective method for inspecting machines to meet industry safety requirements and extend their life. Professionals also ensure maintenance and mitigation measures after NDT to further slow the rate of deterioration.

Quality assurance

Testing with non-destructive means can provide results that are reliable and accurate. NDT testing does not damage components, which makes it possible to test all equipment and machinery, minimising inaccuracies and irregularities in the test results. This adds a level of assurance to the operator's safety to know that all machinery in a factory undergoes regular testing and complies with standards.

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Improved products

It is possible to notice flaws in greater detail because of advanced imaging technologies and accompanying software used in non-destructive testing. This helps in optimising production processes and leads to better product design. The detection of critical defects improves product reliability and ensures customer satisfaction.

Uses Of NDT

There are many ways in which professionals can use NDT, which vary from simple visual testing to the use of complex machinery and equipment for flaw detection. A common use of NDTs is to ensure that all components of a system work together by testing each component separately and then observing how they perform together. Another popular use for NDT is to identify and characterise detail that might be a cause of future errors, such as a plumbing system with a potential for leaks. Various industries use NDT, which include:

  • Aerospace industry: The aerospace industry uses NDT technologies, such as ultrasonic testing equipment, to test airframe structures for strength and wear and tear.

  • Oil and gas industry: The industry uses ultrasonic and radiographic technologies to inspect the internal structure of equipment for voids, cracks and welds.

  • Biomedical and medical devices: This industry uses non-destructive testing techniques, such as ultrasounds and x-rays.

  • Civil and construction industry: NDT ensures that the materials used to construct buildings are able to withstand large stresses to improve their longevity.


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