Selecting an appropriate NDT method:
Every NDT method has its own advantages and disadvantages.
Some methods are more suitable for detection and evaluation of certain flaws than others. As product quality requirements vary, so do the inspection requirements. Size, location and orientation of material flaw that is acceptable in one industry does not necessarily imply acceptance in a different industry.
Product quality acceptance criteria are usually specified by industrial standards, in some cases national or international standards. Often, clients have their own customized requirements.
NDT method selections will depend on material tested, nature or type of defect, size, location, and inspection speed among others.
FLAW DETECTION USING ULTRASONIC INSPECTION (UT)
The ultrasonic material evaluation method is based on transmission of acoustic waves into material under examination. Any material that transmits mechanical vibrations can be tested. Ultrasonics detects a variety of flaws, both linear and non-linear, and permits three-dimensional interpretation. Defect orientation can be longitudinal, transverse and oblique. Lamination can also be detected. Other applications include wall thickness, coating thickness and corrosion measurement.
Principle of flaw detection:
The UT instrument converts electrical pulses into mechanical vibrations or waves. These waves travel across the tested specimen and reflect from flaws because of their different acoustic nature. The returning reflected waves are re-converted to electric energy and displayed as signals on a cathode ray tube (CRT). The position and size of these signals correspond to the position and size of the flaws. Flaw evaluation is often difficult. Complex electronic equipment is required especially when high speed multi-channel defect detection is called for. Ultrasonic testing is highly suitable for automation.
SonoTron (TM) is a Multi-Channel Ultrasonic technology used for inspection of Tubes & Pipes, Round bar, Square bar, Hexagonal bar, Plate, Rails, Wheels, Axles, Brake liners, Composites, Aerospace parts and Automotive parts.
SonoTron (TM) is a registered trademark of NDT Technologies Inc.
Eddy Current Method
FLAW DETECTION AND EVALUATION USING EDDY CURRENT INSPECTION (EC)
Eddy Current inspection is used only on electrically conductive materials, and is suitable for detection and evaluation of surface and subsurface flaws.
Principle of flaw detection:
An energized electric coil induces a magnetic field into the tested specimen. The fluctuating magnetic field generates an electric eddy current. The presence of a defect in the tested material increases the resistance to the flow of Eddy Currents. This change is electronically analyzed to provide information on flaw severity or condition of the material. EC technique is suitable for automated high speed inspection applications. The method is non-contact, and complex-shaped objects can be non-destructively evaluated.
Just like Ultrasonic instruments, EC instruments can be small and portable or large multi-channel devices. EC inspection is the most widely used NDT tool.
Eddy Current and Ultrasonic testing methods compliment each other. Used in combination, they enable full reliable volumetric material inspection.
Eddytron (TM) is a Multi-Channel Eddy Current technology used for inspection of Tubes & Pipes, Round bar, Square bar, Hex bar, Plate, Sheet, Foil, Rails, Wheels, Axles, Composites, Aerospace parts and Automotive parts.
Rototron (TM) uses rotating probes for inspection of flat or round materials. For inspection of complex shapes, custom designed probe arrays are utilized.
Eddytron (TM) and Rototron (TM) are registered trademarks of NDT Technologies Inc.
Laser measurement is non-contact. It works in reflective or non-reflective modes. A high level of fundamental accuracy can be achieved. Laser is also suitable for high temperature measurement. Profile, dimensions and straightness can be measured at production speeds. Optical measuring devices are suitable for many applications, including complex-shaped surfaces.
On-line systems for optical evaluations of material surfaces are available. This method can be applied in addition to eddy current testing.
RADIOGRAPHIC INSPECTION (RT)
RT uses penetrating radiation and works on the principle that denser or thicker materials will absorb more radiation. The specimen is placed between a source of radiation and a sheet of radiographic film or image amplifier. A flaw present anywhere within the specimen will absorb less radiation than the specimen itself. An area of higher or darker exposure will indicate the flaw's presence and location.
Complete systems for radiographic examinations are avaiable from 5kV to 450kV. Portable or stationary equipment is available.