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The Different Methods of Non-destructive Testing (NDT)



Non-destructive testing (NDT) is essential when you need to evaluate the integrity of your material. By using non-intrusive tactics, NDT keeps harmful accidents at bay by searching for any defects to the material. These methods do not harm the materials, allowing you to continue using the property after it has gone through NDT. At ARC, we specialize in various forms of NDT and want to cover some of the most common testing methods that we offer in-house. If you are trying to understand the differences between methods, you have come to the right place. Our experience conducting NDT throughout the years makes us a valuable resource.


Fluorescent/Dry Magnetic Particle (MT)

This process utilizes strong magnetic fields to find any breaks, cracks, or gaps near the surface. MT works on materials that have a high susceptibility to magnetic fields, like iron, cobalt, and nickel. This testing method helps find any areas that may result in a leakage before it is too late. The magnetic particles will be attracted to any discontinuities in the material so you can know the exact location that needs repair.


Liquid Penetrant (PT)

Low viscosity fluid, meaning it flows easily, is used in PT to help find any cracks in a material. This fluid has a visible dye that will help reveal imperfections. As the fluid moves across the surface, it will flow into any crevice, marking the flaw. Once the fluid has had time to travel across the whole area, a developer will be applied that forces the liquid upward. This creates a clear trace of where the crack is located. The types of penetrants that can be used in this process include solvent-removable, water washable, and post-emulsifiable.


Visual Inspection (VT)

Visual inspection is one of the most basic and common ways to find imperfections on a material. This process is a surefire way to ensure that the material remains undamaged during the inspection. There are two ways to conduct VT: with the naked eye or with a remote visual inspection tool (RVI). By using the naked eye, inspectors will examine a surface with a flashlight to find any imperfections. The other way to conduct a VT is by using a robot, drone, or another tool to move the inspection camera around and examine the material through the footage it captures.


Ultrasonic Thickness Testing (UTT)

If you need to measure a material, coating, or lining’s thickness, a UTT needs to be conducted. This helps you ensure that the material is reliable and will be able to function properly moving forward. By putting a transductor against the surface, it measures the material’s thickness which can provide insight on if any corrosion has taken place. It is a completely safe method, and your team can even continue operations while the test is underway.


Brinell, Rockwell, or Vickers Hardness Testing (HT)

Metal hardness testing is crucial to ensure that a project is up to par. Different types of metals require different testing methods. The three most common types of HT are Brinell, Rockwell, or Vickers.


Brinell HT

This is the first hardness test that became a common practice in the industry but is still widely used today. The Brinell HT uses 1mm to 10mm diameter steel to indent the surface. Using a microscope, the mark is examined and measures the indentation hardness. This method is ideal for rough materials.


Rockwell HT

The Rockwall method is the most popular HT because it is less intrusive than the Brinell method. It uses a smaller indenter, thus leaving behind a smaller indentation. It is an easy option and can be used on a wide range of materials.


Vickers HT

The Vickers HT combines accuracy with minimal force to create an accurate, pinpoint test. The diamond indenter is even smaller than the one used in a Rockwell HT. This allows microelements on the surface to be targeted but the material must be properly prepped before the testing takes place.


Positive Material Identification (PMI)

A PMI test can be used to evaluate the chemical makeup of a material. It is used to ensure that the material has all the key elements and can withstand corrosion. It is an essential test for quality control and safety compliance. This test can identify when the wrong material has been used or if there is a mix-up in alloys. PMI either uses an X-ray Fluorescence (XRF) analyzer or an Optical Emission Spectroscopy (OES) to conduct the test. XRF is the most common and uses a device to scan the properties of the material. However, it is limited because it cannot scan carbon or lighter elements. If you need to detect every element, the OES is a better option.


If your team needs NDT to meet inspection requirements, consider using ARC! We ensure that every job we complete meets the highest standards of innovation, quality, and productivity. You can learn more about our services here!

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