NDT Knowledge

Radiographic Testing (RT)

This NDT method is most widely used all over the world. This method uses X or Gamma radiation as probing energy and Film as a recording medium. Other techniques of this method uses Imaging Screen or suitable imaging system.

It is an internal examination method and most sensitive to volumetric defects (Porosity, Slag inclusions). In order to get maximum sensitivity the defect must be parallel to the radiation beam. As the angle between major axis of the planar defect and radiation beam increases the defect sensitivity decreases rapidly.
Radiographic testing is a time consuming process. The exposed films has be processed in order to decide the acceptability of the part being tested. The cost also relatively high compared to Ultrasonic or Magnetic or Penetrant testing methods.

Radiation safety also an important aspect that is always to be addressed according to local statutory.

Please follow the links if you need more information:

1. For basic science – NDT Resources
2. For detailed RT – NDT Resources – RT | Kodak – Radiography in Modern Industry

Ultrasonic Testing (UT)

Ultrasonic Testing also one of the most widely used NDT method. This method uses ultrasound as a probing energy and CRT or LCD as a display. The new equipments includes digital display, saving and print options.

This method is relatively fast. The equipment must be standardized with calibration blocks in order to understand and evaluate the indications. It is an internal examination method and highly sensitive to planar defects (Cracks, Lack of fusion) rather than volumetric defects such as porosity or slag inclusions

The contact testing and immersion testing are two main methods widely employed. The reliability of testing highly depends on the operator skills.

For basic science – NDT Resources | Nondestructive Testing Encyclopedia -UT from ndt.net
For detailed UT – NDT Resources – UT

Magnetic Particle Testing (MT)

Magnetic Particle testing is a surface and sub-surface testing method which uses electromagnetic energy for probing and ferromagnetic particles as indicators. This method is limited to test ferromagnetic materials. It is a simple method and more sensitive to linear defects. As the depth of defect increases, the sensitivity decreases rapidly. It is a cheap and fast testing method. A defect under the influence of magnetic field produces leakage field which attracts the magnetic particle sprayed on the specimen surface. Maximum response obtained from the defects that are perpendicular to the magnetic lines of force.

Either dry or wet particles are used to detect indications. Fluorescent particles are used to increase sensitivity. The following magnetizing currents are used in the Magnetic Particle Testing:

  • AC
  • DC
  • Single Phase HWAC
  • Single Phase FWAC
  • Three Phase HWAC
  • Three Phase FWAC

For basic science – NDT Resources
For detailed UT – MT – NDT Resources – MT

Liquid Penetrant Testing (PT)

Liquid Pentrant Testing is a surface testing method. All non-porous materials can be inspected by this method. In order to be detected, the defect must be open to surface. This is an easy and cheap testing method most widely used in all industry.

When a penetrant is applied on the suitably cleaned material surface, it is driven into the defect by capillary action. The capillary force depends on the physical properties such as surface tension, the contact angle, and the size of the defect opening. The developer applied on the surface after the excess Penetrant removal bleed out the penetrant trapped inside the defect and produce visible indication.

For detailed literature on PT – NDT Resources – PT

Electromagnetic Testing (ET)

Leddy Current Testing and Magnetic Flux Leakage Testing are tow main categories under this method. This method is applicable to surface and subsurface testing of all conductors. The system needs to be standardized in order to detect discontinuities and evaluate indications. Once standardized, the testing can be done faster and results are instant. This method relies on the principle of electromagnetic induction. It is a non-contact testing method.

An alternating electrical field introduced in a coil induces alternating magnetic field around the coil. When the energized coil is placed on the test surface, the alternating magnetic field induces eddy current on the test material. This eddy current produces an opposing alternating magnetic field and provides load to the coil. This load is measured and displayed on a Meter or CRT or Chart.

The contact testing and immersion testing are two main methods widely employed. The reliability of testing highly depends on the operator skills.

For basic science – NDT Resources
For detailed UT – ET – NDT Resources – EC | Eddy current Testing by B.P.C.Rao

Visual Testing (VT)

Visual Testing is perhaps the oldest of all testing. Basically light photons acts as probes and human eye or suitable recording medium function as detector. The modern visual inspection is classified in to direct and indirect methods. Suitable lighting is an important aspect in visual testing. It is performed with naked eyes or with aid such as lens, mirrors and instruments such as borescope, videoscope.

It is an importance testing method because many of the NDT methods ends with visual testing.