NDT(Non-Destructive Testing): A Detailed Guide

NDT(Non-Destructive Testing) is the Technology to assessing of Soundness and acceptability of an actual component, without affecting the functional properties of component itself.

Introduction to NDT– 

Basically, NDT is the group of testing, Where Defects or discontinuity can be known, without affecting the actual and functional properties of the material.

To perform NDT testing various type of equipment is used, and with the help of this equipment, the defects or any discontinuity can be known in the given time.

NDT & NDT Methods are known as the best sources to test the component in the minimum amount of time and save money and time for the organization.

NDT(Non-Destructive Testing) is also known as-

1. NDE (Non-Destructive Examination)

2. NDI (Non-Destructive Inspection)

Now, Giving you a brief analogy of NDT above, We both going to dive into the detailed guide of NDT, Here you are going to know about the same, from basics to advanced levels of Information. I hope, After reading this, Your all questions will be washed out.

So, Without Further delay, Let’s get started-

What is non-destructive testing?

As I discussed earlier, Nondestructive testing (NDT) is the practice of looking for flaws or differences in a material, component, or assembly without damaging the part’s or system’s capacity to function normally.

In other words, when the inspection or test is completed the part can still be used.

NDT requires various Inspection tools (As I discussed earlier), But Sometimes it is not mandatory to use those tools at all, They can be performed through the naked eye, Known as Visual testing as I will discuss later in this guide in the NDT Methods Section.

Why Use NDT

NDT has its various benefits in terms of uses, Here are some points to consider while thinking about why use NDT-
  • Accident Prevention– As the name says, It reduces the chance of accident due to its process of Inspection, where you don’t need to break the component or move anyway(if not possible to move), This gives flexibility and reduces the chances of any horrible condition to happen.
  • Enhance Product Reliability– While casting or manufacturing the product, various types of defects may come like Slag, porosity, and so on, which downgrade the quality of component and if gone without inspection, thus can cause some serious issues in the future, So Technician or Authorized person inspect the component to know, if there is any defects or discontinuity is present or not, this tells about product quality and if there is any discontinuity is present, then component or product is further sent to repair. This can increase product reliability and increase quality.
  • Reassurance–  NDT gives reassurance on the product because when the product is inspected through the preferred NDT method, It gives clarity about Product quality and reliability.
  • Cost-Efficient– Basically, NDT relies on Third-party inspection, So the organization doesn’t need to be equipped with NDT equipment. They need to call an NDT company to inspect their products, Which saves the various costs of equipment and manpower cost. Although NDT tells you the quality and reliability of the product, hence its saves any further expenses in the long run.

Where Used NDT– 

Here is some of these sectors where NDT is used, Mention below-
  1. Mechanical Engineering
  2. Electrical Engineering 
  3. Civil Engineering
  4. Aeronautics Engineering
  5. Forensic Engineering
  6. Petroleum Engineering
  7. System Engineering 
  8. Chemical Industry
  9. Mining Industry
  10. Gas Pipe Line 
  11. Medical Industry
  12. Art.
➤There are two types of testing available in the testing sector-
  1. Destructive Testing 
  2. Non-Destructive Testing 

Destructive and Non-Destructive testing– 

Destructive and Non-destructive testing are types of NDT method, both are used in industrial sectors or their concerning sectors, varies with the requirement.
Destructive Testing–  Destructive Testings are those, where a component or product or metal is bent, altered, stretch and de-forms its shape to test its strength and load-bearing capacity, where deformation of product is needed, known as Destructive testing.
Types of destructive testing-
  1. Corrosion Testing
  2. Facture and Mechanical Testing
  3. Fatigue Testing
  4. Hydrogen Testing
  5. Pressure Testing
  6. Residual Stress Measurement
Know more about destructive testing in detail.
Non-destructive Testing– As I discussed earlier above, Non-destructive testings are those, where a component or product is tested without any destruction or deformation.
✦Now, it’s time to discuss NDT methods, Where I will discuss various NDT methods, which are used in various sectors in Industries.

09 Most Commonly Used NDT Methods

There are 9 most commonly used NDT methods, which is discussed below-
  1. Visual Testing (VT)
  2. Radiography Testing(RT)
  3. Ultrasonic Testing(UT)
  4. Magnetic Particle Testing
  5. Dye- Penetrant Testing(DPT)
  6. Eddy Current Testing(ET)
  7. Leak Testing(LT)
  8. Hydrogen Testing(HT)
  9. Magnetic Flux Leakage(MFL)

1. Visual Testing(VT)– 

The most widely used in all NDT techniques is Visual Testing(VT), and it is the oldest of them.

As the name suggests, the authorized person looks visually at the component or product, if any cavity is presented above the surface of the product, which can be visually identified, then the product is further sent for repair.
If not, then based on the visual inspection, further NDT methods are applied.
➤Read In-depth about Visual testing

2. Radiography Testing(RT)

Radiography testing is an NDT method based on the principle of differential absorption of penetrating radiation by the object under test.

Owing to the varying characteristics or composition of the structure of the test object, different amounts of penetrating radiation.
The radiation passing through, without being observed is recorded on the film and viewed on an illuminated screen. The picture thus seen is used to locate defects in the test object.
Fig. The principle of Radiography Testing-
Radiography principle


Read more about Radiography Testing

3. Ultra-sonic Testing(UT)-

In this inspection method technique, High-frequency sound waves are sent to the object under test.

The sound wave travels through the material. During their path of travel, they suffer the loss of energy which is reflected at interfaces. A receiver probe picks up the reflected wave and analyzes this signal to locate flaws in the object under inspection.

Sound waves follow the laws of optics in their propagation. Further, the velocity of propagation of sound in various metals has been very accurately determined. The time taken by a sound pulse to travel through a material is a direct measure of the length of the path traveled by it.

Ultra-sonic can detect cracks, laminations, shrinkage, cavities, flakes, pores, and other discontinuities.

 Fig. The principle of Ultra-sonic testing-
<img data-src="ultrasonic principle.jpg" alt="ultrasonic principle">


Read in-detailed about Ultrasonic Testing

4. Magnetic Particle Testing(MPT)– 

Magnetic particle testing is a very useful method for the detection of surface and sub-surface cracks in ferrous material components.

In this method, when the part being inspected is first magnetized, there is a flow of magnetic lines of force on the portion under test.
At this stage, magnetic powder is sprayed on the surface, if there is any discontinuity or flaw in the surface or just below it, the flow of magnetic lines is interrupted and intermediate poles are induced at either side of the discontinuity.
These interpoles attract the sprinkled magnetic powder. This forms an exact image of the flaw, which is shown down below. The image is sharper if the flaw is closer to the surface.
One thing to be kept in mind, during magnetic particle testing is the discontinuities parallel to the lines of magnetic force will not show any indication.
Fig. The principle of Magnetic Particle Testing


magnetic particle testing


Read Detailed Guide on Magnetic Particle Testing

05. Dye-Penetrant Testing(DPT)- 

This is an aided visual technique and it is also known as Liquid Penetrant Testing(LPT).

In this method, a bright-colored liquid that penetrates into cracks and fissures open to the surface is used.
First, the surface is thoroughly cleaned and wiped clean. A penetrant is sprayed onto the surface. The bright-colored penetrant seeps into all surface flaws.
Now, the surface is carefully wiped clean to remove all the excess dye on the surface. A developer is applied to the surface. The white-colored developer has a blotting action on the dye and draws it up to the surface.
A bright-colored indication of the flaw is presented to the inspector. Dye-penetrant testing is shown in Fig.
Fig. The principle of Dye-Penetrant Testing
dye penetrant principle

Read In-depth About Dye penetrant Testing

06. Eddy-Current Testing(ET)

When a moving or changing magnetic field passes through a conducting material, it induces a current in it.

A magnet pulled across a sheet of copper or aluminum will produce irregular current flow, including whirlpools very similar to those found in the wake of a ship. These turbulent and irregular electrical currents are called eddy currents.

Though these currents are random in nature, they produce their own magnetic field which creates a dragging force between the plate and the magnet. this phenomenon is used for non-destructive inspection of non-magnetic but conductive material.

In this technique, an alternating current (frequency ranging from a few kHz to several MHz) is sent through a coil. This coil is moved along the test surface. The current flowing through the coil induces an eddy current in the test object.

These eddy currents have their own magnetic field which is picked up by a sensor probe moving along the excitor probe. As the probe transverses the surface cracks, etc. result in the distortion of eddy current which are reflected and displayed on the chart or cathode-ray tube screen.

This technique is applied in cracks detection and material sorting, thickness determination of conductor, paint coating thickness check, and surface roughness gauging.

Read a detailed guide on- Eddy current testing

7. Leak Testing(LT)-

Leak testing is defined as ” the process of identifying leaks in vessels or pipes, to detect the defects.

A high-pressure gas or liquid flows through a vessel if any defects are present in the vessel, These defects create pressure differences within the vessel, and liquid or gas flows from high pressure to lower pressure.

Read in-depth Guide on- Leak testing

08. Hydrogen Testing(HT)-

The hydrogen test is performed for those materials, which are prone to get corroded when exposed to Hydrogen.

09. Magnetic Flux leakage(MFL)-

Magnetic flux leakage testing is a method of no-destructive testing, which is used to detect corrosion and pitting.

In this technique, a powerful magnet is used to magnetize in the conductive material to detect defects, Magnetic field leaks from there if any corrosion or volume losses are presented.

Here is a video guide to learn more, Give a watch-

Benefits of NDT

NDT is the backbone of any Manufacturing Industry. The industry needs to rely on NDT testing to elevate its reliability and Quality, to ensure credibility in the market.
In this context, I am sharing some benefits of NDT, which further enhance your knowledge about NDT.
Some of the points can be considered from why use NDT, because of relevancy !!
So, here are some benefits of the NDT-
  •  Reliability–  NDT measures the quality of the product. It checks if any defects of discontinuity are there or not, without altering them. This gives the product a stamp of Accept or Reject. If any cavity will be there, then that product will be rejected and go for further repair. This gives quality reliability to the manufacturer before using that product and saves from any hazardous happening in the coming future.
  • Safety–  Some of the industrial Manufacturing are heavy in load and some of the components like pipes in Gas pipelines are risky. This can cause a tremendous hazard and loss if gone unchecked before actually using the product. So, to get ensure, NDT test is done to prevent upcoming losses or accidents. So, NDT testing performs a big role in Industrial safety or in other sectors, where NDT is used.
  • Quality Control- NDT basically runs on codes and standards(Discussed down below), which allow us to monetize and regulate the overall Quality of the product. These codes and standards give flexible acceptance criteria, which further allow us to control over quality.
  • Quick Setting Time- NDT equipment is easy to set up. It takes a minimum of time if the technician or Qualified person is well trained and has experience in those testing. The result of Quick setting is less downtime.
  • Less Mobility- Some Industrial parts are heavy to move or Some parts may be fixed or maybe in use and you know that NDT equipment is easy to mobilize. This makes testing faster and saves from unnecessary moves of the components or parts.

Non-destructive testing applications-

There are several Applications of NDT, Some of which are given below, have a look at these applications of NDT-
  • To monitor, improve, or control manufacturing processes
  • To inspect for in-service damage 
  • Inspect of raw products
  • To ensure product integrity and reliability
  • To maintain uniformity in quality level

Codes and Standards of NDT

NDT uses several codes and standards to maintain the quality of inspection and reliability of NDT. Codes and Standards are generally a Constitution of NDT, in general language.
Codes and Standards of NDT guides- What to do, How to do, And what will be the criteria of inspection.
Here are Various organizations, who authorized to create Codes and Standard of NDT –
  • ASTM (The American Society of Non-Destructive Testing)
  • ASNT  (American Society for Testing & Materials)
  • ASME (American Society for Mechanical Engineers)
  • API      (American Petrolium Institute)
  • AWS    (American Welding Institute)
  • AIA      (Aerospace Industries Association)
  • NBBI   (National Board of Boiler and Pressure Vessel Inspectors)
  • ISO      (International Organization for Standardization)
  • CEN     (European Committee for Standardization)
  • PED      (European Pressure Equipment Directive)

Training And Certification of NDT

There are various training as well as certifications, That certify and train a person to be involved in NDT testing.
We all know that without proper training and required certification, the person is not allowed to operate equipment or be involved in any kind of NDT testing.
 NDT offers three levels of certification which include Level-I, Level-II, and Level-III in approximately all methods of NDT.
Level-I – When a person is certified with Level-I certification, the person is qualified to do certain NDT procedures including Calibration, Equipment setups, and inspecting some of the objects.
Level-II – When an Authorized person is certified with level-II, The person can perform various procedure including approx all objects that comes under the NDT testing under the instruction of Codes and Standards.
Level-III-  Level-III is considered as the highest level of Certification in the NDT sector, When a person is certified with level-III, the Person is able to inspect, monitor, interpret codes and films, and measure quality guidelines in selected methods.

➤Training and Certification offered from various NDT organization, that offers various levels of training and certification in selected NDT methods. Here are some organization that offers training and certification in NDT methods-

Organization for Training and Certification

American Society of Non-Destructive Testing(ASNT)

A globally established organization, which offers NDT persons, A broad level of certification and training including all methods of NDT.

ASNT offers, ASNT Level-II, ASNT Level-III, ASNT Central Certification Program (ACCP), and Industrial Radiography and Radiation Safety Personnel(IRRSP).


Here is the link to the ASNT website, where you can find various training institutes across the world direct from a website.

British Institute of Non-destructive Testing(BINDT)

An accredited certification organization that offers a Personnel Certification In Nondestructive Testing(PCN).

International Standards Organization (ISO)-

ISO 9712 (Non-destructive testing — Qualification and certification of NDT personnel) is a published standard that details the requirements for qualification and certification of personnel that perform NDT.

American Petroleum Institute (API)-

API offers numerous Individual Certification Programs (ICPs) specific to NDT personnel in the petroleum and petrochemical industries

Natural Resources Canada (NRCan)- 

NRCan manages the Non-Destructive Testing Certification Body (NDTCB) which offers a Canadian General Standards Board (CGSB) certification.

These Were some organizations, which offer personnel, various training, and certification in various NDT methods.



NDT is the broad sector that ensures the security and reliability of the products and hence helps to build trust over the industry.
Most of the NDT methods are designed to deliver the highest quality output, which makes NDT, a priority choice for needed industries.
Here, In this article, I have covered mostly all the topics regarding NDT and Its methods and I hope you got a broader perspective and knowledge regarding the same.
Thank you for staying here and giving your time and in response gaining some knowledge.
Hope to see you soon. Bookmark us to know more about NDT and don’t forget to share with the needy one or your mate to help him grow also.

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Non-destructive testing pdfnon destructive testing pdf
Q. How many methods of NDT are there?
Ans.  There are nine methods of NDT-
  1. Visual Testing(VT)
  2. Radiography Testing(RT)
  3. Ultra-sonic Testing(UT)
  4. Magnetic Particle Testing(MPT)
  5. Dye-Penetrant Testing(DPT)
  6. Eddy-Current Testing(ET)
  7. Leak Testing(LT)
  8. Hydrogen Testing(HT)
  9. Magnetic Flux leakage(MFL)
Which NDT method is best?
Ans. It depends on the requirement and you can not choose which method is best. All methods have their own importance in terms of uses.
Q. Why is NDT used?
Ans. NDT is used based on the various points cover through the NDT, Some are here-
  • Accident Prevention
  • Enhance Product Reliability
  • Ressourance
  • Cost-Efficient
Q. What is the difference between destructive and non-destructive testing?
Ans. As the name suggests, The major difference between Destructive and Non-Destructive testing is-
In Destructive testing, an object is altered, stretched, bend to test. In Non-Destructive Testing, the Object is not distorted by any means to test the object. In NDT, NDT methods are used to test the object.
Q. What are the advantages of using NDT?
Ans. There are several advantages of NDT, Some of them are down below-
  • Reliability
  • Safety
  • Quality Control
  • Quick Setting Time
  • Less Mobility
Q. Where is non-destructive testing used?
Ans. There are various sectors and industries are there, where NDT is used-
  • Mechanical Engineering
  • Electrical Engineering 
  • Civil Engineering
  • Aeronautics Engineering
  • Forensic Engineering
  • Petroleum Engineering
  • System Engineering 
  • Chemical Industry
  • Mining Industry
  • Gas Pipe Line 
  • Medical Industry
  • Art


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