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NDT of Metals

Nondestructive testing of metals

NDT of metals – cutting-edge equipment for the PA UT (phased array) and PE UT (pulse-echo).

Principle of PA UT method:
The probe consists of small transducer elements
Allows to change transducer parameters electronically

  • Transducer size;
  • Beam steering;
  • Refraction angle and focal point;

Beam steering of individual elements



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• NDT of metals – other methods VT, PT, ET, MT
• Certification of NDT technicians in accordance with ČSN EN ISO 9712

PT method
Liquid penetrant testing is non-destructive method used for the detection of open surface cracks and discontinuities of various shapes and sizes, even in non-porous and non-metallic materials (i.e. copper, aluminum, ceramics, glass, rubber, plastic).

Types of liquid penetrant testing:
– Dye penetrant inspection
– Fluorescent penetrant inspection
Crack detection is usually visual, but for fluorescent inspection a CCD camera can be used. Recognition capability of human eye is approx. 0.09 mm from the 30 cm distance.
The advantage of liquid penetrant testing is its sensitivity to very small cracks, possibility of complex geometry specimen testing, applicability within the production process (liquid penetrant line for bulk component inspection), portable technical equipment and easy operation.
The disadvantage is, that it detects only surface flaws on unabsorbing material, risk of misinterpretation for polluted surface and necessity for access to the tested object.

VT method
Visual testing is one of the very old diagnostic inspections. Its relatively low time consumption and low price makes it the most available non-destructive method. It is performed by naked eye or with magnifying glass.
Indirect inspection is performed using an endoscope, incl. systems using miniature TV cameras with the appropriate manipulators and lighting.
Borescopes are rigid and inflexible endoscopes with probe diameter 0.9 to 16 mm, tube length between 0.06 to 1.6 m and observational focusing distance between 1 mm to infinity. Optical device incl. a probe forms a rigid unit with the lens at one end and the eyepiece at the other end.
Fiberscopes alias fiber endoscopes transmit the image by fiber light waveguide. Picture waveguides of endoscope consist of up to 200 000 fibers with the diameter approx. 10 microns. Exposure waveguides consist of approx. 60 000 fibers. Videoscopes on probe tips are equipped with a CCD chip, which in comparison with fiberscopes allow significant improvement in resolution and truly reproduced colors.
Industrial videomicroscope replaces conventional microscopes in those cases where the inspected sample cannot be placed in their field of view. The reasons may include excessive dimensions, weight and non-transferability of the sample – i.e. large castings, coachworks, piping, machinery products (turbines). It is possible to inspect for example weld details, surface treatment, wear rate or damage of the components. The specially designed sensor head, which can be loosely attached to the inspected surface, is a combination of removable microscopic lens and CCD scanning chip.

ET method
Alternating current field of the coil induces in the material eddy currents. According to Lenz’s law the eddy current field counteracts the excitation field. The resulting field is given by the vector sum of both fields.
The endpoint of resulting vector is shown in the phase plane on the display. The resulting field is mostly influenced by surface cracks perpendicular to the flow of eddy currents.

Probes can be classified according to the orientation to the test material:
– Surface probes
– Bobbin probes

It is also possible to classify probes according to the winding arrangement:
– Absolute probes
– Differential probes
– Absolute reflection probes
– Differential reflection probes
– Special probes

MT method
The principle of this method is material magnetization and evaluation of the magnetic flux variance in the vicinity of the defect. Physical principle of the method lies in local cross section reduction of ferromagnetic material and increase of the magnetic resistance at point of surface or subsurface discontinuity…
The basic requirement for material magnetization is correct inductive line orientation – perpendicular to direction of the expected discontinuity. The longitudinal magnetization detects transversely oriented cracks and the transverse magnetization detects longitudinally oriented cracks in material.

Simulation of ultrasonic testing, ultrasonic field and defect response in CIVA software: