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Non-destructive testing and technical diagnostics
NON-DESTRUCTIVE TESTING (NDT) – research method used for detection of object’s internal defects without its destruction.
It is used by production and operation of vitally important goods, components and constructions (houses, railways, aircrafts, sea vessels, fuel- and gas-piping, and other equipment).
Principal methods of non-isotopic non-destructive testing and technical diagnostics:
X-RAY INSPECTION
Radiation control methods differ in detection modes of flaw-detective information and are divided into
- radiographic
- radioscopic
- radiometric.
Radiographic methods of radiation non-destructive testing are based on transformation of controlled object radiation image into radiographic image or record of this image with the following transformations into light image.
Depending on detectors used the following ones may be distinguished:
- film radiography (photosensitive film serves as a detector of a hidden image and as the recorder of a statically visible image)
- xeroradiography, semiconductor plate (common paper is used as a recorder).
Radiation introscopy.
Non-destructive testing method consisting in transformation of object’s radiation image, being under control, into the light image on the output screen of radiation and optical transducer, provided that the analysis of the received image is carried out in the course of testing.
Radiometric fault detection.
Information acquisition method on product’s internal condition being under control and ionizing radiation in form of electrical signals (of different rate, duration or quantity). His method provides the highest possibilities for control process automatization, control automated reverse communication and product manufacture technological process. The advantage of this method is in the opportunity to carry out continuous high-productive goods quality control caused by equipment used high response rate. This method is as good as the radiography by sensitivity.
Dye penetrant inspection
Dye penetrant inspection of non-destructive testing is the simplest non-destructive testing method used for detection of continuous structure surface and through defects. It detects defects with the surface outlet. The method is based on the capillary penetration in the middle of the indicator fluid defect with the following recording of indication traces. It is widely used for the control of welding joint integrity.
Defect detection process using dye penetrant inspection is divided into 5 stages.
- stage 1– previous surface cleaning.
- stage 2– penetrant application.
- stage 3 – release of penetrant overflows.
- stage 4– developer application.
- stage 5 - inspection.
According to regulatory documents the sensitivity class is specified depending on detected defects size. Sensitivity of flaw-detective materials is set on control samples.
There were set 5 sensitivity classes (by the lower threshold) depending on defect sizes.
|
Sensibility class |
Defect disclosure width, μm |
|
I |
under 1 |
|
II |
Of 1 to 10 |
|
III |
Of 10 to 100 |
|
IV |
Of 100 to 500 |
|
Technological |
not defined |
Magnetic particle inspection
Magnetic particle inspection is used in a number of industrial branches: metallurgy, machinery engineering, shipbuilding, construction (steel structures, piping), etc.
Magnetic particle inspection is intended for detection of surface and undersurface defects spreading deep into the product, in the different sizes objects made of ferromagnetic materials, materials with non-magnetic coating.
This is one of four classical non-destructive testing methods connected with the use of devices and flaw-detective materials for NDT.
Magnetic particle inspection is an independent technological process and includes:
- preparation of product surfaces for inspection
- parts magnetizing
- parts surface finishing with dispersion (powder)
- parts checkup
- demagnetizing
- process quality control