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The field of Non destructive Testing (NDT) continues to grow in importance. This is largely due to the need for manufacturers to ensure quality control while keeping costs low. In other words, businesses must find a way to reduce the number of defective parts produced by testing finished products rather than inspecting raw materials.
Test failures are costly, especially when they result from undetected flaws that lead to damaged parts, failed machinery or scrapped batches. Non destructive testing (NDT) is an inspection technique that detects characteristics without damaging the test object. It’s a cost-effective way of inspecting metallic and non-metallic surfaces, volumes and components without altering their original properties. For example, during a non destructive test, we cannot change the size, shape or surface finish of an object in any way.
What Non Destructive Testing Can Find?
While each test has its own strengths and weaknesses, Non destructive testing can detect the following flaws:
- Cracks and breaks: Any sudden change in the object’s physical properties could be a sign of a break or crack. For example, if the inside of a pipe changes from smooth to gritty, or if the outside surface feels sticky or gooey.
- Corrosion: Corroded metal is hygroscopic, which means it absorbs water. When enough moisture gets inside a pipe, it can create a weak point that leads to a catastrophic failure.
- Defects in surface finish: If a surface is pitted or irregular, it may not seal properly. In the case of a pump or valve, it could lose its ability to create a vacuum or pressure.
3 Most Common Forms Of Non Destructive Testing
Magnetic Particle Inspection
This method uses a magnetic field to reveal surface and subsurface flaws. It’s the best non destructive test for finding corrosion, pitting, inclusions and other defects that can’t be seen with the naked eye. It can also find cracks in ferrous and nonferrous metals of all types, including stainless steel, nickel alloys and aluminium.
Liquid Penetrant or Dye Penetrant Inspection
This type of non destructive testing is commonly used to detect cracks, voids and other flaws in steel, aluminium, copper and other metals. When you apply the penetrant, it soaks into the surface and penetrates internal flaws. It then turns the surrounding area into a vibrant colour that’s visible to the naked eye. The advantage of this method is that it doesn’t require the part to be removed from service.
Magnetic Particle Susceptibility Test
This type of non-destructive testing verifies the surface condition of ferrous metals and detects the presence of cracks. It’s useful for detecting internal corrosion, which can lead to failure. It’s also used to find areas of high or low distortion in ferrous metals, which can affect the part’s contouring and tolerance.
Benefits Of Non Destructive Testing
- Reduced scrap rates: Finding flaws early can prevent them from getting worse. It can also enable you to replace or refurbish the part rather than scrapping it.
- Improved productivity: Finding flaws early allows you to correct them. In some cases, it may even be possible to repair the part.
- Preventative maintenance: You can use non destructive testing methods to find smaller flaws before they turn into bigger problems. In some cases, it may even be possible to repair the part.
- Reduced costs: Most non destructive testing methods are relatively inexpensive. In some cases, it may even be possible to repair the part.
- Reduced risk of injuries: When a part breaks, it can cause serious injuries. Finding flaws before they lead to catastrophic failure can reduce the risk of injuries.
Known Limitations of Non Destructive Testing
- Interpretation of test results can vary
- You may need to remove some parts from the service
- You must inspect all critical parts
- You may need to replace some parts
- You may need to reassemble the product
- You may need to change the product design
- Testing can be time-consuming
