Nondestructive testing (NDT)

One of the industry most important tasks is product quality in different areas of human activity. Key point is reliability and safety in hazardous environment of aviation, nuclear power, hydro power, explosive hazards in oil and gas production and refinery and chemical industry.

Nondestructive testing (NDT) is process to evaluate structure faults in different objects without damage by using proper equipment. NDT methods are developed to find different type of failures like integrity failures, change in dimensions, physical or chemical material features.

Electromagnetic, sound, radiation and other signal conversions are in use to examine quality of parts, joints, units and etc.

Nondestructive testing (NDT) inspection is control method to evaluate unit/joint reliability and material properties with no need of dismantle equipment or interrupt in operation routine.

Faults may form and show up in any materials by several causes:

  • Work in harsh environment conditions;
  • Dynamic load;
  • Material technology specification failure;
  • Linear expansion.

NDT methods:

Any fault shall cause to change in material physical feature or structure: density, integrity, conductivity, tension and etc. Analyzing of these parameters is base of modern NDT methods:

  1. Visual testing. Borescopes, cameras or other optical applications might be used to view internal surface, deep holes of inspected parts. Visual inspection allows to find fault of surface structure like fractures, holes of 0.1mm to 10 µm size.
  2. Magnetic-particle inspection is used on ferrous materials involving of fine iron particles (in liquid or dry powder) that applied to the part while it’s magnetized, so particles will be attracted to fault areas. It may detect subsurface fractures up to 2mm deep in material structure.
  3. Eddy-current method is based on measuring change in impedance in the testing coil during passing fault material sample. Areas of up to 20mm can be inspected, also suitable for automatization control.
  4. Ultrasonic method is based on propagation of ultrasonic waves in the material tested.
  5. Liquid penetrate inspection (LPI) or penetrant testing (PT). This method is based on enhancing contrast of fault area vs. normal surface. It makes possible to visually find thin surface cracks and other material faults created during manufacturing or operational routine. Low surface force penetrant is applied to the test component and fill in surface-breaking discontinuities. Inspection is performed under UV or white light, depending on type of dye used - fluorescent or visual.

 

DPI (Dye penetrant inspection) sensitivity allows to discover surface cracks of 0.02mm thickness. But penetrants and developer chemical are too toxic and irritant, that limits more wide application of this method.

 

So Nondestructive testing (NDT) of parts, jopint and units in oil industry is key factor of safety.

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