All you need to know about NDT

Nondestructive testing (NDT) or NDI OR NDE can be defined as the process in which materials or components are inspected, tested and assessed for disruptions.

To test the physical properties of components, destructive methods are implemented. But the NDT technique ensures the analysis of these structures without causing any wreckage. NDT is used in manufacturing, inspections and fabrications to check its integrity and stable features.

The main advantage of NDT lies in the technique providing indestructive results of a product’s reliability and accuracy, controlled manufacturing processes, and lowered production costs. NDT Companies also ensures the usefulness and safety of the product to the clients by laying more emphasis on its integrity.

 

METHODS OF NDT TESTING

 

There are several methods of NDT testing, but some of the current ones are:

  • Visual examination (VT)
  • Vibration Analysis (VA)
  • Leak testing (LT)
  • Laser Testing Methods(LM)
  • Acoustic emission testing (AE)
  • Thermal /Infrared Testing (IR)
  • Magnetic flux leakage (MFL)
  • Magnetic particle testing (MPT)
  • Microwave Testing (MT)
  • Ultrasonic testing (UT)

  1. Visual testing (VT)– There are discontinuities and misalignment in parts of components which can be observed by the observant by just viewing. This NDT method is the most common one is used in the industry. This inspection can be performed by direct viewing, or aided with instruments such as mirrors, magnifying glasses, remote viewing through computer-assisted systems. This helps in evaluating the parts to detect deformities easily.

  1. Vibration Analysis (VA) – This inspection involves checking vibration signatures from rotating machinery to assess the equipment. There are three types of sensors mainly used in this NDT method, i.e. displacement sensors, velocity sensors and accelerometers.
  2. Leak testing (LT) – As the name suggests, leak testing is the analysis of leaks from systems. This inspection is performed in 4 different techniques, i.e. bubble leak testing, pressure change testing, halogen diode testing and mass spectrometer testing.

  • Bubble leak or as the name implies is checking gas leakages usually air from pressurized systems. The solution stands in the immersion of these parts in a tank of liquid or spraying of soap in the affected area, which creates bubbles to evaluate the affected area.

  • Pressure change testing – unlike a bubble test, the pressure test can be performed only on closed systems. Vacuum or pressure on the system is generally pulled off to check and control the pressure. What symptoms can be noted as loss of weight? Changes in temperature, loss of influence over the set period indicate faulty parts of the system through this NDT method and corrected accordingly.

  • In halogen diode testing, halogen detectors or “sniffers” are used with a mixture of air and halogen gas tracer to detect leaks.

A helium air mixture sniffer is used in the test chamber with a sniffer in the mass spectrometer technique. After surveying the surface, it sends air samples back to the spectrometer to indicate a leak.

  1. Laser testing methods: this method can be into three laser used techniques; Holography, Shearography and Profilometry.
  2. The holographic method uses a laser which detects the deformities on the surface of the equipment .the result of the laser beam scanning results in a topographical map like presentations to compare it to undamaged samples to check the defects.
  3. Laser shearography: this method incorporates superimposition of two patterns by applying laser light on the surface of the component being tested. The image is coupled with a CCD charge couples device and saved up on a computer. Now the tested surface’s picture is taken. The superimposition of both these patterns will show the defects and voids in the material.
  4. In the method of profilometry, three essential things are used, i.e. high speed rotating laser light and miniature optics and a computer with high-speed digital signal processing software for the detection of defects which is obtained by surface topography of 3d Images.

Magnetic Flux Leakage (MFL)

This process uses a powerful magnet to induce magnetic fields which saturate steel structures like pipelines and storage tanks. A sensor is later used to measure changes in magnetic flux density which show any reduction in a material that occurs due to pitting, erosion or corrosion.


Microwave Testing

This method is used for dielectric materials, and as the name suggests, microwave frequencies are transmitted and received by a test probe. This test probe detects changes in dielectric properties like shrinkage cavities, pores, foreign materials or cracks, and it displays the results in B or C scans.

Liquid Penetrant Testing (PT)

Liquid penetrant testing is the process in which a fluid that has less viscosity is used in the testing process. This fluid flows down into any defects like cracks or porosity before a kind of developer is applied, which lets the penetrant liquid to seep upwards and create a visible indication of the error. This tests can be conducted by using solvent removable penetrants, water washable penetrants and post-emulsifiable penetrants.