Non-destructive testing

Non-destructive testing (NDT) of materials allows to inspect the quality of products and to detect the presence of imperfections without destroying their integrity or properties from a physical, mechanical or structural point of view.
These methods are applicable in castings, forgings, rolled products, pipes and welded joints in metal manufacturing and processing, pre and in-service testing of equipment, installations and structures, railway maintenance and aerospace, also in military industry, archeology, etc.
Controltest Ltd is accredited by the Executive Agency “Bulgarian accreditation service” according BDS EN 17020/2012 as an Inspection Body type “A” (Certificate №52OKA) for the following methods of non-destructive testing

Radiographic testing
Conventional radiography
  - Computed radiography
Radiographic methods are based on exposing optically non-transparent objects to X-rays or gamma rays.
Indications of a defect are displayed on a radiographic film or a monitor and consist of variations in the intensity of the radiation passing through the tested material.
These methods allow detecting of surface and subsurface indications such as porosity, undercuts, slag inclusions, gas and metal inclusions, cracks, lack of fusion and penetration etc.
Ultrasonic testing
Ultrasonic inspection permits detection of surface and subsurface defects.
The method is based on the propagation of the ultrasonic waves in the object or material tested.
The method permits detection of internal flaws in the materials such as discontinuities, cracks, lamination, gas and slag inclusions, incomplete penetration and changes in structure, even at a long distance from the surface of material.
 Ultrasonic thickness measurements Ultrasonic inspection permits wall thickness determination, used for corrosion inspection of vessels and piping.  
Dye Penetrant testing Dye penetrant methods are based on the capillary effect of liquids.
Defects are apparent in high optical contrast between penetrant (color or luminescent) sucked out of the surface discontinuities and the developer  used.
Surface discontinuities such as irregularities, cracks, undercuts, surface pores and lack of fusion can be detected. A limitation of this method is that it cannot be applied to materials with surface porosity.
Magnetic-Particle testing
Magnetic particle testing is based on the distortion of the magnetic field when crossing irregularities and discontinuities on the surface of magnetized material.
Surface and near-surface (around 2mm) discontinuities can be detected.
A limitation of this method is that it can be applied only on ferromagnetic materials.
Magnetic rope testing (MRT)
The instruments for electromagnetic and magnetic steel rope nondestructive testing (NDT) are based on the general principle: detection and evaluation of changes in the distribution of magnetic flux created by a magnetization system in a rope under test. The changes occur because the rope part under test contains irregularities, like wire breaks or a section with corrosion or abrasive degradation. Magnetic flux leakage arising close to the broken wire can be detected by a sensor as the changes of the magnetic flux around the rope (or through it) are caused by changes in the rope cross-section area.   
Visual testing  Visual methods are based on using of different kinds of optical equipment to amplify the abilities and sensitivity of the human eye.
Surface discontinuities such as porosity, cracks, undercuts, erosion, and corrosion as well as other mechanical damages at the material surfaces can be detected, even at difficult to access locations.
Leak testing
 Leak testing is a method applicable for detection of discontinuities passing through the entire thickness of the material, as well as testing high pressure and vacuum equipment. The method is based on deliberately exceeding the vacuum or pressure parameters than those the equipment is designed to bear.
Continuity of coatings and insulation   /Holiday test/  Holiday test involves applying a high voltage over the surface of an insulated conductor.
Holiday test or a Continuity test is one of the nondestructive test method applied on protective coatings to detect unacceptable discontinuities such as pinholes and voids, that are not readily visible. 
Vibration measurements
and vibration state analyses of rotating machines, vibro – diagnostics
Vibration measurements and analysis are diagnostic methods that detect the vibration characteristics of the examined object. The information is collected by vibration sensors. The vibration analysis is performed on the basis of the amplitude-phase characteristics recorded.
The method is applied to rotating elements of electrical and industrial mashines. 
Eddy Current testing
Eddy current inspection relies on the detection of eddy current disruption when inducted in objects. In general, the induction of eddy currents is carried out by a coil. The same coil is often used for the detection of field disturbances too.
Those disturbances in the current density through the object can be caused by surface roughness, corrosion, inclusions, cracks, discontinuities, differences (partial effects caused by differences in the heat treatment regimes) in hardness, conductivity, magnetic permeability and material structure.
Eddy Current Methods detect surface and subsurface discontinuities. They can be used in measuring of coatings thicknesses layed over ferromagnetic and non-feromagnetic materials, as well as for sorting of materials.  
Hardness tests:
  • Vickers
  • Rockwell
  •  Brinell
  •  Shore
Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. It can be applied to metals and their alloys, welded joints, castings, forgings, formed, rolled and drawn as well as parts produced by them.
Dimensional measurements. The measurement of the geometric dimensions of the parts are designed to ensure their geometric accuracy. Precision requirements to detail guarantee its operation in the assembled unit. Deviations of linear and angular dimensions of the details of the nominal values are determined depending on the functionality of these dimensions for the purpose of details.  
Chemical analysis of metals:
Alloy analysis
Alloy analysis are based on using spectral and X-ray non-defractable methods. They are used to precisely identify alloys by evaluating their content and the quantity of the constituent elements, as well as other inclusions.
The applied methods are:
  • Atomic emission spectrometry of carbon and stainless steel (incl. “C”, “P”, “S”), as well as aluminum and aluminum alloys.
  • X-Ray spectrometry of steel, aluminum and brass alloys. (PMI).