Non Destructive Testing
Non Destructive Testing (NDT) is defined as the inspection, testing or evaluation of a material, part, mechanism or machine without causing wear or damage on it. The objective of NDT is the detection of defects, flaws or functional deviations.
Non Destructive Testing (NDT) offers the ability to evaluate the condition of a material / component / mechanism / machine, to assess its suitability for use, to check the conformity of its characteristics with the specifications, to estimate its operational lifetime, to specify the time and the type / extent of its potential maintenance or repair.
Our company applies Non Destructive Testing on welds on materials, parts, welds and rotating machinery with methods such as:
- Visual Testing
- Penetrant Testing
- Μagnetic Particle Testing
- Ultrasonic Testing
- Eddy Current Testing
- Radiographic Testing
- Vibration analysis
Although the method is quick and easy to apply, it is of the first order of importance and requires experience. It can be performed during all stages of production / construction work, and can give important information regarding the defects and the integrity of the part / structure, the variables affecting the work and the general conformity to the specifications.
(LIQUID) PENETRANT TESTING
Liquid Penetrant Testing is a relatively simple and sensitive method that allows the inspection of a large variety of materials and components. It is applied to both magnetic and non magnetic materials. It is used to detect defects that intercept the surface of the part, such as cracks, laps, porosity, shrinkage areas, laminations, and similar discontinuities, by utilizing liquid penetrants that seep into surface flaws by capillary action. These flaws may be inherent in the original material, result from the fabrication / construction process, or develop from usage and / or corrosion.
MAGNETIC PARTICLE TESTING
Magnetic Particle Testing is a non destructive technique used to detect surface breaking or slightly subsurface defects. It is performed by spraying magnetic particles on the surface and then imposing a magnetic field on the inspected area. Surface or subsurface discontinuities in the material such as cracks and linear defects affect the magnetic field, causing a magnetic flux leakage, and attract the magnetic particles. Hence, the magnetically held particles outline the defect and indicate its location, size, shape, and extent. The application of the method is limited to ferromagnetic materials.
Ultrasonic Testing is one of the most widely used NDT methods today for the detection, mapping and evaluation of internal discontinuities in metals and other materials. It is a method of volumetric testing and requires a skilled operator / inspector. The basic principle of the technique involves directing a high frequency sound wave into the material on a predictable path, which is reflected back from any interruption in the material continuity, such as cracks, porosity, shrinkage cavities, laminations, disbonds, etc. The reflected beam produces a signal that is amplified and usually displayed on a suitable screen, and then analyzed to define the presence, the type and the location of the flaw. Inclusions and other inhomogeneities in a material, which cause partial reflection or scattering of the ultrasonic waves, can also be detected by the UT method.
EDDY CURRENT TESTING
Eddy current testing is a method of non destructive inspection that is based on the phenomenon of electromagnetic induction. When alternating current is applied to the conductor (with regard to the matter at issue the excitation coil of the probe of the control device), an alternating magnetic field develops around the conductor. If another electrical conductor (the material under inspection) is brought into the close proximity to this magnetic field, eddy currents will be induced in this second conductor. These eddy currents generate their own magnetic field, which interacts with the initial field (through impedance). If there is a discontinuity or a conductivity / magnetic permeability variation in the material under testing, then the eddy currents flow is disrupted and their magnetic field is altered. This variation is detected by the control device (either by a secondary coil (receiver coil) inside the probe, or by the change of the alternating current of the primary coil (excitation coil)) and points out the existence of the defect through a corresponding indication on the device screen. Eddy currents are used on electrical conducting materials for the detection of surface and subsurface defects, detection of corrosion, coating thickness measurements, material identification, heat damage detection, heat treatment monitoring, etc.
Radiography is used when the overall / through thickness soundness of a material / part is to be evaluated. RT can detect defects that are completely internal and located well below the surface. Our certified and highly experienced personnel utilize electromagnetic radiation produced by portable X-Ray tubes to penetrate the area / object of interest, record images on photographic film and interpret the radiographs. The whole radiographic process is performed under strict safety rules.
Our specialized personnel can undertake special tasks and responsibilities on the field of NDT such as:
- Reviewing NDT standards, specifications and procedures, and translating them into practical testing instructions adapted to the actual working conditions.
- Reviewing quality assurance / quality control program regarding the applied non destructive inspections.
- Reviewing / Verifying welding procedures and personnel qualifications.
- Interpreting and evaluating of test results according to applicable codes, standards and specifications.
- Organizing and reporting results of non destructive tests.