What is Nondestructive Testing?: Your Ultimate Guide

Introduction 

Perhaps the most important part of any quality assessment in production operations such as welding is the ability to check the strength and integrity of the resulting component with great accuracy. Also, ascertaining the consistency of welding operations is essential to most manufacturing processes. However, the usual way of confirming the consistency of these components was by using destructive testing methods, which often proved costly. A sample will usually be deemed unusable after undergoing a destructive test. Fortunately, technological advancements have provided better quality assessment methods that are non-destructive. 

This article is the ultimate guide that gives you all the information about non-destructive testing, the different types, and their applications in industrial production and manufacturing. If you’re ready to learn more, ensure you read until the end.

I. What is the Definition of Non-destructive Testing (NDT)?

Regardless of the obvious inference from the name, which hints at the fact that there is no destruction of samples when utilizing non-destructive testing, NDT truly encompasses much more. Firstly, it is a broad classification of a range of testing methods that often require different tools and levels of sophistication to perform a quality assessment of components. You can think of it as a large door that opens to a big house with smaller doors that lead to different rooms. These other rooms represent the various types of non-destructive testing methods, utilities, apparatus, and set-ups. However, the main objective of the different types of non-destructive testing methods remains the same – the components remain undamaged and can be reused in production after the test. 

Again, non-destructive testing (NDT) has been identified under several names, some of which include non-destructive evaluations, non-destructive inspections, and non-destructive examinations. Nevertheless, the underlying non-destructive nature of the procedure remains. Additionally, the medium of testing, which often depends on the particular non-destructive testing method, is a major difference. For example, ultrasonic testing uses high-frequency sound waves, and eddy current testing uses magnetic fields as a medium for testing. Still, test samples remain intact regardless of the testing medium used by a non-destructive testing method. 

This guide gives an exploration into other non-destructive testing methods and their various mediums of testing. However, it is instructive to know that visual inspection is not categorized as a non-destructive testing method considering that it doesn’t require any tool for inspection. It only requires the use of sensory organs like the eyes. In contrast, non-destructive testing methods require some form of testing equipment and set-up with varying levels of complexity depending on the unique testing method employed. Also, different levels of minimum standard requirements exist for several NDT methods. For the test equipment, standards are provided to ensure the safety of users and support personnel and for a better cost-effective way of meeting quality requirements.

II. What’s the Purpose of Non-destructive Testing (NDT)?

In a nutshell, the primary aim of non-destructive testing is to ensure that test samples remain intact after the testing. This way, you can still integrate the test components into the final product or system. Most importantly, it helps to avoid the risk often caused by fatigued components during their service lifespan. The utility of destructive testing is often in ascertaining the permissive stress a piece can endure before its failure. However, non-destructive tests often confirm the nearness of a component in service to set limits for failures. These assertions then validate the use of non-destructive testing for verifying the integrity of members while they are still in service. This feat will mean a complete system breakdown if destructive testing is employed for components while in service. 

Nevertheless, destructive and non-destructive testing can be considered complementary rather than conflicting. While destructive tests establish limits of failures, non-destructive tests crosscheck the state of a functional element against those determined breaking points. It also allows field technicians to recommend repairs or replacements appropriately for affected components. 

The risks to life and livelihood associated with the failure of a working component can be colossal, especially for moving parts like turbines and facilities like oil pipelines and nuclear reactors. Hence, the cost-to-benefit ratio is often the yardstick for most non-destructive tests.

III. What are the applications of Non-destructive Testing (NDT)?

As expected, non-destructive testing has the most use cases in the manufacturing industries. Still, other sectors, especially where heavy motion equipment is a massive part of the operation, require non-destructive testing in no small part. Here are some industries where non-destructive testing is a primary requirement of the major activities. 

• Manufacturing – When manufacturing industrial equipment and components, companies ensure their products’ quality using non-destructive testing. These organizations understand the risk that components as small as a bolt can or a weld can pose to the integrity of a huge device like a vessel if it is below quality requirements. These NDT procedures are suitable for detecting porosity, cracks, corrosion, and welded joints. Plus, manufacturing components are monitored by regulating bodies with severe consequences, including heavy fines in the event of a non-conformance to set industry quality requirements. 
• Automotive – This industry relies on NDT procedures to ensure the integrity of the material, fitting components, and production procedures like welding used in manufacturing vehicles. It ensures the safety of the buyers and the passengers of these vehicles. A single mishap traced to a defective component can lead to enormous losses for the automotive company in fines and reputation, often resulting in the loss of customers and revenue. 
• Oil and Gas – Another huge dependent industry on NDT, the oil and gas industry relies on NDT for various reasons, including the safety of workers and the communities where oil facilities and infrastructures are located. Pipelines that carry various products can cause severe damage to the environment if not properly evaluated for defects like inconsistent welding and material thickness requirements. What’s more, these facilities are harder to test on the field using testing methods other than NDT. 
• Aviation – This industry is very sensitive and strictly regulated by law to ensure the safety of airline passengers, seeing that a single plane crash can result in a huge loss of lives. Periodically, NDTs are carried out to ensure the reliability of moving parts like propellers, rotors, and blades to guarantee a safe trip for passengers. While different NDT methods like UT and eddy current testing are used, the components remain intact after the testing. 

IV. What are the requirements for Non-destructive Testing (NDT)?

An advanced testing method like non-destructive testing should establish standard requirements to guide industries and professionals in ensuring human safety and quality compliance. However, different requirements exist for different localities with some overlap between industries. Still, the essence remains the safety of users of the finished product, equipment, or facility. 

These requirements often emanate from research carried out by research and development teams within the manufacturing industries and international standard bodies like ASTM and ISO. Nevertheless, global trade associations like ASNT and ICNDT contribute to this research. These requirements often give guidelines to NDT professionals on appropriate testing methods to evaluate specific parameters. 

Also, the areas of components to test and the permissive limits for the values obtained during testing are some requirements for non-destructive testing. Additionally, the equipment requirements and set-up, testing frequency, and reporting format and storage are all part of the specifications for NDT. These requirements form the frame of reference, especially for manufacturers, airlines, and oil and gas companies, as they have some of the most complex facilities and equipment requiring NDT. 

V. What are the Training and Certification for Non-destructive Testing (NDT)?

Proper and adequate training for NDT professionals is necessary if they operate NDT equipment and carry out the tests effectively. Moreover, the advances in NDT technology have come a long way and keep advancing with new findings and a new body of knowledge to keep NDT professionals on their toes. But while certifications are one of the ways stipulated by NDT regulating bodies for NDT professionals, experience counts significantly to the efficient use of NDT equipment and accurate execution of NDT tests. Nonetheless, training and courses are often huge steps to getting certified as an NDT specialist, with different levels representing more advanced knowledge as you go up the levels. Generally, three levels of proficiency exist for NDT certification, denoted by levels I, II, and II, corresponding to basic, intermediate, and expert levels of expertise, respectively. 

At the bottom of the certification ladder is the level I NDT technician who is required to understand the NDT process of at least one method of NDT test. Setting up testing equipment and calibration and generating a satisfactory report for a minimum of one type of NDT test is also required for certifying a level I NDT technician. Additionally, being able to observe safety precautions for one NDT testing method is expected. 

The requirements for the level II technician include an advanced understanding of standards and test methods and how they relate to NDT testing. Also, they should thoroughly understand the strengths and vulnerabilities of NDT methods, including familiarity with in-house and industry standards and codes. All these requirements are in addition to level I requirements. 

At an Expert level, also known as level III, an NDT technician’s requirements include interpreting industry codes and standards to generate working documents, procedures, and method statements. These documents should facilitate industry best practices and should be best suited for the organization’s NDT test methods. 

VI. What are the Common Methods of Non-Destructive Testing (NDT)?

While any NDT method’s primary objective remains to preserve the test components, you should note that not all NDT methods are identical. NDT methods employ different mediums, including magnetic fields, high-frequency sound, and fluids, to detect anomalies. In essence, these methods have different suitability and best use cases. Here are the common ones highlighted below. 

• UT (Ultrasonic Testing) – High-frequency sound can travel through materials revealing any discontinuities based on the time it takes to reach the receptors. This medium is used in UT to locate defects hidden within various components and materials and often requires ultrasonic probes to produce and receive sound waves. However, depending on the number of probes required and their configuration UT can be classified as Through Transmission (TT), Pulse Echo (PE), and Time of Flight Diffraction (ToFD). 
• ET (Electromagnetic Testing) – This NDT method has three varieties: remote field testing, eddy current, and alternating current field measurement. ET, in simple terms, uses an electric current or a magnetic field as a medium for identifying flaws and anomalies within a component by passing a current through the element. However, generating the magnetic field determines which type of ET to use since a probe or alternating current can be used to generate the required magnetic field. 
• RT (Radiographic Testing) – X-rays are the common radiation for this NDT test. The rays penetrate the test components, revealing hidden defects like discontinuities and porosity. The results are shown on a film or with computer tomography, which is basically a digital film. However, thicker materials may require Gamma rays to locate defects effectively.  
• PT (Penetrant Testing) – Also known as Liquid Penetrant Testing, it utilizes the flow of fluids into notches that indicate the presence of a flaw, such as cracks, voids, and other forms of porosity. A developer is often a material that pulls out the fluid from the pores in the component giving the technician a representation of the flaw. 
• MT (Magnetic Particle Testing) – For ferromagnetic materials, this NDT method is very suitable and effective, as it uses an electromagnet to create a magnetic field that is used to detect flaws. A leakage in the magnetic flux highlighted with magnetic particles signifies the presence of discontinuities in the test sample. 

VII. What’s the difference between each Non-destructive Testing Method? (Use table)

Several differences exist between the different non-destructive methods, including their applications, defect suitability, speed, hazards, set-up, and limitations. Here are the important differences highlighted in the table below.

VII. What’s the difference between each Non-destructive Testing Method? (Use table)

Standards, codes, and specifications specified by international and local NDT regulatory bodies are often the go-to documents for recommending or selecting an NDT method for specific applications. However, these standards are only secondary to the law and its requirements. Also, standards and recommendations are sometimes given by NDT equipment manufacturers to guide technicians on the best practices for carrying out an NDT procedure. Nevertheless, a level III NDT technician can recommend a suitable NDT method or process for an application if all the above fail to give clear guidance. But some NDT methods are particularly appropriate for field assessment, while some are suitable for laboratory procedures. For instance, Ultrasonic Testing is often used for many on-site quality assessment operations. Still, the equipment required for some NDT methods may be very sophisticated and may be the only factor for selecting a non-destructive test over another.

Additionally, some NDT equipment may be more suitable for on-site work, while others are ideal for the laboratory. In any case, selecting the right NDT equipment significantly depends on getting a reliable manufacturer with a track record of quality delivery and a commitment to innovative testing solutions. One such is NDT-KITS, which has over 35 years of industry experience delivering bespoke and innovative testing solutions for various industries. With satisfied customers worldwide, NDT-KITS has enjoyed unwavering loyalty from its numerous clients, who have continuously given favorable reviews of their products and services. What’s more, NDT-KITS offers one of the most competitive prices in the industry, helping customers meet their testing objectives without breaking the bank.

Conclusion

So, what does this all mean? For NDT technicians and professionals from different industries where non-destructive testing is an integral part of their operation, understanding standard NDT methods, their applications, and their limitations are critical. Also, a grasp of the different requirements stipulated by law and regulatory NDT bodies, including specifications, codes, and standards, is essential for NDT professionals. However, equipment, tools, and machinery used in different NDT procedures are vital for the success of these operations and getting a suitable supplier like NDT-KITS is often a game-changer. NDT-KITS has more than three decades of quality delivery of NDT solutions with an extensive portfolio of bespoke and standard NDT solutions for client-specific applications. Now that you fully understand the non-destructive test, what’s your next move?