There are a lot of non-destructive testing methods. With just visual observations or magnification, it is quite difficult to locate the deformities in the materials, such as forged metals, cast, and welded metals. Therefore, proper nondestructive methods will only help in finding out such indications without causing any harm to the components.
In this post, we are going to read about a few NDT methods along with the safety precautions one must follow while executing these methods.
Non-destructive Testing Methods:
Liquid Penetrant Testing
Magnetic Particle Testing
1) Liquid Penetrant Testing
The liquid penetrant testing non-destructive testing method is utilized to identify cracks, breaks, pores, or similar deformities which are actually open to the metal's surface or any other solid substance. First, the substance that has to be examined is cleaned properly.
After that, a penetrant is applied to the surface of the substance, and within a time frame, it's drawn into the defects by capillary action. Then the penetrant is deleted from the surface but remains in the surface opening until the developer removes it.
➤ Most of the entrants that are utilized are organic compounds that might cause dermatitis.
➤ Therefore, skin contact must be avoided, followed by strict practices of good personal hygiene.
➤ In the test region, smoking or its elements, food, or drinks must not be stored or utilized.
➤ Before consuming anything, exposed skin must be washed properly.
2) Ultrasonic Testing
Ultrasonic waves are produced by an electric generator which tends to supply high-frequency voltage to a piezoelectric crystal. Basically, three ultrasonic methods have been developed; they are — the resonance method, the reflection method, and the transmission method.
➤The equipment must be disconnected from the power supply.
➤ The condensers get discharged whenever a cathode ray tube is removed or adjusted.
3) Magnetic Particle Testing
Magnetic particle testing is one of the most common nondestructive testing methods for forging. It makes use of magnetism in order to attract and hold extremely fine magnetic particles right on the part itself. If there is a presence of a defect, it interrupts the magnetic field and is clearly depicted by the pattern created by the particles.
The material is then magnetized in a favorable direction by DC line voltages which are transformed to low voltage (4 to 18 volts), high amperage AC, three phases of full wave current, and half wave current.
➤ Every electric circuit must be installed and grounded in accordance with the National Electrical Code or any other code.
➤ Local exhaust must be provided in order to control the dust particles that are utilized for testing.
➤ If the local exhaust is not conceivable, the operator must wear respiratory protective equipment.
➤ Also, personal protective equipment must be worn to safeguard against possible skin irritation from the powder.
➤ The operator must also wear eye protection to protect against the irritating effect of the dust particles.
4) Radiography Testing
Radiography testing makes use of X-rays and gamma rays. X-rays are unidirectional rays, and their wavelengths can be varied within certain restrictions in order to suit the conditions. Moreover, X-ray radiography and gamma radiography actually differ from each other. Gamma rays are multi-directional, and their wavelengths, being usual of the source, cannot be controlled.
➤ Each & every source of ionizing g radiations is actually dangerous. They must be stored and managed according to the instructions of the supplier of the source.
➤ The direct exposure to radiation by the operations must be monitored on a regular basis, according to the instructions of the suppliers.
➤ Only skilled, trained, and certified operators must be allowed to execute the work.
➤ The test area must be effectively cordoned off, and you must ensure no one enters this space.
➤ Operators working in the area must be medically assessed at a frequency recommended by the supplier of the source.
➤ The work must be performed in a suitable, enclosed area.
➤ After the work is completed, the source must be stored according to the instructions given by the supplier
5) Electromagnetic Testing
There are two types of electromagnetic tests that are in use currently — eddy current testing and magneto-inductive testing. The eddy current testing makes use of alternating current in a coil or probe in order to induce an eddy current in the material being examined. Variations and flaws in properties or geometry result in changing the distribution & strength of the eddy current.
The magneto-inductive method uses variations in the permeability of magnetic components to develop variations in a pickup probe or coil.
The read-out is displayed on a cathode ray tube or meter, by a favorable or visible alarm, or by a combination of these two methods.
➤ In some reader frequency testing installations, operators faced burns internally when they passed between the testing device and the component. Therefore, some special regulations must be formulated and applied.
➤ Also, barriers must be set up in order to prevent operators or any other person from entering these areas.
➤ The recommendations of the equipment manufacturer must be followed in a proper manner.
NDT is generally considered to be a safe testing method when compared to other testing methods. Still, certain safety practices must be implemented in order to protect employees from injuries. The manufacturing industry is the one that makes use of NDT methods to keep their products in harmony and consistency and to make sure that they are better controlled at the time of manufacturing procedures.