Radiography is a process of recording inner and outer defects in three-dimensional objects on a two-dimensional film plane. Radiograph is a permanent recording in the form of a picture on a film. In order to create a radiograph we need a strong source of energy, a testing object and a film on which the permanent recording will be recorded. Radiography is one of the best non-destructive methods of testing because it’s recordings are reliable and durable.
Because of it’s potential health and environmental issues, the person who is operating the testing equioment must be highly trained. The equipment is expensive and complicated (it includes equipment for developing film), and laminar faults (cracks) are easily overlooked (depending on orientation). Many radiography testing techniques are developed according to specific testing needs.
Usual energy sources that are used are:
- X-ray machines
- Iridium 192
- Cobalt 60
- Cesium 137
Radiography testing is ususally used to test: welding joints, forged pieces and drip-mouldings.
Ultrasonic material testing has been in use since the 1940’s since when many different aplications have been developed. Ultrasonic testing is based on the fact that solid materials are good at carrying sound waves. The effect that occurs when the borders of solid materials start to reflect sound waves is used to test material volume.
Ultrasonic testing and radiography are the only two methods for testing volume flaws. With the appropriate knowledge and by using modern techniques ultrasonic testing has become one of the best non-destructive testing methods.
Soundwave reflection doesn’t just occur on the outer borders of the material, it also occurs when the sound wave collides with the inner flaws of the material. With those kind of properties ultrasonic testing and radiography has become the most common method for testing the inner material flaws. It’s worth mentioning that both methods, radiography and ultrasound, overlap in just one area of testing, while each method has it’s own advantages and disadvantages.
Some material flaws that can be revealed with ultrasonic testing are:
Magnetic flux is a fairly simple non-destructive testing method. The basic principle is to magnetize the object by applying the magnetic particles which then show the problematic area by accumulation of magnetic particles on parts where the magnetic field is „leaking“.
With the use of magnetic flux it is possible to find flaws on the surface of the object as well as directly below the surface. Materials that can be tested must have magnetic properties (ferromagnetic materials).
This method is used for:
Penetrant testing is one of the first widely accepted non-destructive testing method. The very first techniques used oil and chalk while today many new techniques have been developed which allow very high sensitivity. Penetrant testing method is based upon capillary action. The penetrant is applied on the object, then after adequate penetration time the excess penetrant is removed and a developer is applied. The developer helps to draw the penetrant out of the flaws so that an invisible indication becomes visible.
This method is used for:
Wide application of this method is possible due to it’s ease of use and the ability to work on-the-spot. The ability to use this testing method on nonmetallic materials such as ceramics, plastics, and glass ensures that this method is future-proof.
Visual inspection is the oldest and the most common non-destructive testing method. The purpose of this method is to quickly and efficiently find various surface flaws. This method can be separated to two different testing techniques, direct and indirect. The properties of welding joints need to be controlled during all three phases of welding (before, during and after welding).