MT is especially useful for preventative maintenance of critical parts already in service and for finding defects before parts are put back in service. 

BEFORE WE CAN BEGIN ANY INSPECTION, industry specifications require that the entire magnetic particle system is checked. Requirements include:

  • Lighting
  • Particle concentration
  • Bath contamination
  • Testing of specimens with known defects

To test with MT, the first step is to magnetize the object being tested by passing an electric current through the component. During the inspection magnetic particles are applied to the surface and any cracks will show up as a result of the particles being attracted to the "leakage field." These particles cluster wherever these cracks are, providing a visual indication for the inspector. The inspector can then assess the extent of damage and provide crucial results to engineers for disposition. 

MAGNETIC PARTICLE TESTING (MT) IS AN NDT INSPECTION TECHNIQUE that uses magnetism and its principles to find cracks, also known as flux leakage sites, in metals. 


Photo credit: @grubn_roht

Using direct or indirect magnetism, MT can detect surface and shallow subsurface discontinuities in steels as well as their alloys. 
In order for a material to hold a magnetic field after the passing of electric current, the material must contain nickel, cobalt, and/or iron. Therefore, this technique is not valid where none of these elements are present, such as in: 

  • Aluminum

  • Inconel

  • Composite

ECT Tools in the Field - New Tech and Capabilities

ONE REASON EDDY CURRENT IS A POPULAR NDT TECHNIQUE is that it does not require the removal of paint or protective coatings when testing.

Image Source: Eddyfi

ECT also doesn't require you to close down operations to test. Newer technologies, such as EddyFi's Sharck probes, feature tangential eddy current array (TECA) technology and are capable of positioning, measuring, and sizing cracks in carbon steels up to 7mm (0.28").

WITH TECHNOLOGY IMPROVING EACH DAY, ECT continues to provide accurate, non-invasive testing of assets under insulation.

What is Conductivity?

As relates to the ECT capacity, when it comes to conductivity, we are primarily focused on the electrons of the outermost shell of an atom. When an atom has 1-3 electrons in the outer shell, the material will conduct electricity when the atoms are pushed by voltage.

CERTAIN MATERIALS ARE BETTER CONDUCTORS THAN OTHERS. For instance, according to the International Annealed Copper Standard (IACS), copper is the perfect conductor. This is because pure copper has a base value of 100%. A base value of 100% makes it an ideal material that offers zero resistance and, therefore, is a pure conduit for electricity.

Eddy Current - What Is It? Where Is It Used?


ECT uses electromagnetic induction to detect and indicate surface and sub-surface flaws in conductive materials, including both ferromagnetic and non-ferromagnetic materials. It can also be used to detect coating thickness.

SPECIFIC APPLICATION AREAS INCLUDE in-service inspection of tubing at nuclear and fossil fuel power utilities, at chemical and petrochemical plants, on nuclear submarines, and in air conditioning systems. 

Here are some other areas where ECT comes in handy: 

  • Electromagnetic braking
  • Repulsive effects and levitation
  • Attractive elements
  • Identification of metals
  • Vibration and position sensing
  • Structural testing

What is Visual Acuity?

If you haven't already, you will have an eye exam upon certification as an inspector. No matter how great the technology is at detecting even the smallest of discontinuities, your eyes still must be able to distinguish the results.

NAS 410, ASME Section V Article 9, and SNT-TC-1A require all technicians to be capable of reading a minimum of Jaeger Number 1 or 2 at a distance of 12" for near vision acuity upon initial certification.

So, what is visual acuity?

In simple terms, it’s the ability of the eye to resolve fine details at a given distance. Look at the picture below. Can you read the bottom line at 40cm? If so, you have the ability to distinguish the letters as separate entities from the word. Take the test for yourself:

Visual Acuity.png

Visual Testing - Direct Visual Examination

Have you ever heard an inspector say 'I can already tell that weld is not gonna pass'? It's because the weld doesn't pass the direct visual examination test, or as we call it, the 'sniff test'. The same goes for the old saying," If it looks like a duck ...".

These are all examples of direct visual examinations. Some simple tools used for direct visual examination include welding gages, as seen here being used to check the fillet leg length. These tools, along with the most important tool for visual testing, our eyes, are quality instruments that can determine alignment, dimensions, and indications in all sorts of manufacturing products.

Learn more, request a demo, and see how online training works at

Thank you Instagram user illfabian for the photo:

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Visualizing VT

Visual Testing (VT), the most common nondestructive testing technique. Offering broad potential for many applications while requiring minimal tools, VT is low in cost and easy to apply, often eliminating the need for further types of testing. It is frequently the first step in the inspection process.

Similar to an examination by a physician, visual inspection of the subject is always the first line of defense in determining which further tests are needed to diagnose the problem. Industries that rely heavily on the use an initial VT inspection include structural steel, automotive, petrochemical, power generation, and aerospace.

Although VT is limited to surface-only material examinations, it is often excellent at detecting damaging defects. Remote imaging systems require manual interpretation by technicians. And not even the best technology in the world can replace human interpretation and judgment. At the end of the day, it always comes back to what the technician can see. 

Our VT courses provide you with the knowledge necessary to add this valuable skill set to your toolkit. You can also check out this video with one of our founders, Chuck Hellier, talking about VT.


UT Phased Array - Initial Instrument Setup

The initial setup of phased array equipment for inspection is the most important task for the NDT technician. Why is it so important? Because to do a proper inspection, you will need to be precise, and the right setup guarantees that.

The right setup means you will need to know which calibration method to perform, which probe to use and why, and the characteristics of the material you will be inspecting. And you need to know how to change your calibration each time a transducer or its wedge change. But fear not. Our Ultrasonic Testing courses cover this information and more, ensuring you are thoroughly prepared for your UT inspections. 

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  Credit GemsNDT with the incredible photo!

Credit GemsNDT with the incredible photo!

Phased Array 101 - When is Phased Array Ultrasonic Testing (PAUT) Required?

PAUT is an advanced method of ultrasonic testing with applications in medical imaging as well as in industrial sectors such as construction, power generation, and pipelines. It is particularly useful in the industrial sectors because of its capability for testing a large volume of material, where full volume examination to assess the structural integrity of a design is of critical importance.

PAUT is also a required and an effective method for detecting service-related flaws for cracking, corrosion, and de-laminations as well as for assessing welds and wall thickness measurements, doing corrosion testing, and performing rolling stock inspection (wheels and axles). 

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    Thank you undisputed_kb for the great photo!

Thank you undisputed_kb for the great photo!

At NDT Classroom, we offer several Phased Array courses in which you’ll learn which situations call for PAUT and how to administer the correct applications to get the job done. Check out for more information. 

Ultrasonic Testing - Pulse Echo Technique

Knowing what technique to use, when and how are the trademarks of a successful NDT technician.

That’s why NDT Classroom's online courses focus on ensuring students fully understand different applications of techniques and how and when to implement them. For example, let’s look at the pulse echo technique (also known as reflection), which the following image demonstrates: 

Ultrasonic Testing Pulse Echo.png

This image is an example of a standard compression wave technique reflecting sound from the back wall or discontinuities. The image is used to assess the integrity of the test material for service. In order to obtain a reflection, it is necessary for the reflector to be oriented so that part of its surface is parallel to the scanning surface, otherwise known as 'normal' to the beam. Laminar discontinuities and volumetric discontinuities like gas pores and nonmetallic inclusions are all suitably orientated. However, discontinuities that are angled to the scanning surface may not reflect at all or may reflect the sound away from the transducer.

This may all sound Greek to you now, but after a thorough explanation and demonstration by one of our UT course instructors, you’ll be understanding pulse-echo technique (and many other UT testing techniques) in no time. 

Answering the Inverse Square Problem

The inverse square problem in our recent post asked a question that all RT techs should be able to answer.

It not only applies to technique development, but also safety. Since the intensity of radiation is inversely proportional to the square of the distance, the answer is as follows: If I1 = 28 R, I2 = 2R, D1^2 = 9 feet, then D2^2 = 11.2 feet.

NDTC_answer to inverse square problem.png

Try it for yourself and see online training work.

10 Advantages to Taking Online Classes



An interesting article published on the OPEN EDUCATION DATABASE website presented 10 advantages of taking online classes.  

While not specifically written for NDT-ers, it is certainly relevant for students seeking training in our industry and is reprinted here in its entirety to share with those interested in understanding why online training works:

The current challenges facing traditional colleges and universities, including higher tuition, budget cuts, and course shortages, have caused many students to search for alternatives. With nearly 3 million students currently enrolled in fully online degree programs  and six million taking at least one online course as part of their degree program, online education has clearly become one of the most popular higher education alternatives. The continually improving reputation of online learning has also helped fuel its expansion, as initial skepticism has faltered in the face of evidence that shows that online learning can be just as effective as face-to-face education.

All of this means that students, from working professionals to recent high school graduates, find many reasons to take all or some of their courses online. Below are 10 advantages to online learning.

  1. Variety of programs and courses: From traditional four-year universities to completely online career colleges, higher education today offers a variety of options for students. This means that no matter what students wish to study, from nursing to neuroscience, they can find online the courses or degree programs they need. They can also earn every academic degree online, all the way from a career certificate to a doctorate.
  2. Lower total costs: Online programs can be a more affordable option than traditional colleges. Though not all online degrees have less expensive net tuition prices than traditional colleges (link to OEDB article I wrote about college costs), associated costs are almost always less expensive. For example, there are no commuting costs, and sometimes there is also not any required course materials such as textbooks because those are often available for free online. In addition, many colleges and universities have begun to accept credits earned via free massive open online courses (MOOCs), the most recent advance in online education. Free online courses such as these can help students fulfill general education requirements at little to no cost.
  3. More comfortable learning environment: Commercials that featuring online students studying in the pajamas only skim the surface of one of the primary benefits of online education: there are no physical class sessions. Lectures and other materials are electronically sent to the student, who will then read them and complete assignments. Students will not have to fight traffic, find parking spaces, leave work early to go to class, or miss important family time.
  4. Convenience and flexibility: Online courses give students the opportunity to plan their study time around the rest of their day, instead of the other way around. Students can study and work when they are at their peak energy, whether that’s early morning or late at night. Course material is always accessible online, so there’s no need to schedule special trips to a library either. All of this makes online learning a good option for students who need to balance their work and family commitments.
  5. More interaction and greater ability to concentrate: While there is contradictory evidence about the rate of online student participation versus participation in traditional courses, one thing is certain: online courses offer shy or more reticent students the opportunity to participate in class discussions or chats with more ease than face-to-face class sessions. Some students even report that online courses are easier to concentrate in because they are not distracted by other students and classroom activity.
  6. Career advancement: Students can take online courses and even complete entire degrees while working, while in-between jobs, or while taking time to raise a family. This academic work will explain any discontinuity or gaps in a resume as well. Also, earning a degree can show prospective employers that you are ambitious and want to remain informed and prepared for any new challenges.
  7. Continue in your profession: Even if someone wants to complete a degree program, it doesn’t mean that they want to leave their current job. For most students today, college costs mean that it’s necessary to continue working while in school. The previously mentioned flexibility of online degree programs enable students to keep working while also pursuing academic credentials.
  8. Avoid commuting: During snowstorms and thunderstorms, colleges may cancel classes; if they don’t, you run the risk of getting hurt in dangerous driving conditions. Rather than miss important class sessions, students in online courses can always “attend” by participating on discussion boards or in chat sessions, turn in their work on time, and watch lectures or read materials. Many students also find that the amount they save on fuel costs can be substantial if they don’t have to commute to a physical campus in general, no matter what the weather conditions may be.
  9. Improve your technical skills: Even the most basic online course requires the development of new computer skills, as students learn to navigate different learning management systems (LMS) and programs. The skills students learn to participate in their online courses translate to many professions, including creating and sharing documents, incorporating audio/video materials into your assignments, completing online training sessions, etc.
  10. Transfer credits: For college students who want to attend summer classes, but who live too far from their colleges or have to work summer jobs, taking online classes from an accredited college and transferring the credits to their primary college is a good idea. Students will be able to earn college credit while still enjoying their summer vacation or fulfilling the responsibilities of their seasonal jobs. Similarly, if a college or university is unable to offer enough open sections of a required course, students can take the course online at another college and transfer the credits.

These are just a few of the many advantages of taking online classes. Students in online degree programs are able to manage their time, learn the materials that are presented, and complete assignments on their own schedules.

Radiation Safety - Safety & Controlling Individual Exposure

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Can you answer the question shown in the image above?

Just as a good quality test requires a sharp inspector, it also requires a safe inspector. Working with radiation can be dangerous business. It exposes the technician to two types of exposure: acute and chronic. Acute exposure is short-term, high-level exposure. Chronic exposure is long-term, low-level exposure that is usually the result of improper or inadequate protective measures. Both are to be minimized (or, if possible, completely avoided) at all costs. But how?

Some basics of RT safety include:

- ALARA: "As Low As Reasonably Possible"

- Radiation time, distance, and shielding

- Survey meters

What does that mean? And how do you apply that to radiographic testing? NDT Classroom’s Radiation Safety and Radiographic Testing courses will teach you the answers the these questions and many more. With the help of expert instructors and high-definition videos that demonstrate the most current real-world techniques and technology, you’ll learn how to apply the necessary skills to keep not only yourself safe, but those around you safe as well.

Visit the NDT Classroom website at to learn more and see a demo of our courses.  

WANT TO KNOW THE ANSWER? We'll share it in an upcoming blog post - stay tuned!




Radiography II - Imaging Factors

NDTC_examples of radiographic contrast.png

Besides safety, the ultimate goal of the RT technician is to produce the highest quality radiographic image possible in order to assess the fitness of service of the specimen being tested.

Understanding radiographic sensitivity and the characteristics and variables of radiation and film - such as density, contrast, sharpness, magnification, and distortion, and what affects contrast and what affects definition - will help make that possible.

For example, overexposure of a radiography will produce darker images, or higher densities. Likewise, material thickness also affects contrast as radiation exposure is greater upon thinner sections than thicker ones. Figuring out the balance between all these factors will help you produce the greatest radiographic sensitivity, further ensuring your images show the highest amount of detail (and are therefore the most comprehensive image) possible.

NDT Classroom’s online courses in Radiographic Testing offer an in-depth look at the factors that affect the quality of a radiographic image and how to interpret what an image is showing. With high-def, real-world video examples, the courses clearly demonstrate how you as a technician can handle and maneuver variables to get the best image possible, providing you with the means to create better images. And better images = better understanding of any issues, which then = better chances to get at the root of the problem and fix it. And that is, ultimately, the end goal – accurately assessing and fixing the problem in order to create a safer world for all.  

Want to learn more about imaging factors and radiographic testing? Click here for an overview of NDT Classroom's Level I and Level II courses.

A Look at Radiographic Testing


Radiographic testing is an excellent NDT method to learn, as it offers many advantages over other NDT methods for specific applications.

For one, it can be used on a variety of materials and requires very little surface prep. It is also highly reproducible and often uses portable systems, making it easy to use in elevated positions and in the field.

However, it does not come without its drawbacks, such as the potential for health risks if tests are not performed with the utmost care. But administering tests well and being able to produce a high-quality radiograph is only half the battle. RT Technicians also need to be skilled in interpreting and evaluating the results of the tests they perform. To do so, they must be able to rely on their visual acuity and understand the roles that effects and scattering play in film interpretation.

There are three basic steps involved in interpreting radiographs:

1. Detection

2. Interpretation

3. Evaluation

If there are discontinuities present in the test material, they will affect the amount of radiation that passes through. For example, x-rays or gamma rays will pass through porosity with relative ease as compared to the other solid parts of the same material. This will create a higher exposure and result in a darker region of the finished radiograph. This specific, hands-on knowledge is the kind of information you can expect from the Radiographic Testing courses offered by NDT Classroom.

Led by industry expert Gary Larson, NDT Classroom’s Radiographic Testing Levels I and II courses take you through all the knowledge and steps necessary to lay the foundation for becoming a highly skilled radiographic technician. Not only do they provide the know-how, though; they give you the confidence you need to do the job with the highest level of safety.

Find out more about our RT courses here