Inspection Services

Indian industries are dealing with fierce competition and struggle to reduce the lead time of the project due to untimely services of Non-destructive testing. Achieving a significant reduction in lead time of the project, while improving product quality, was considered impossible. However, at Terahertz, we understand the importance of time & contingencies and provide on-time services to our clients.

Liquid Penetrant Testing (PT)

The principle of liquid penetrant testing is that the liquid penetrant is drawn into the surface-breaking crack by capillary action and excess surface penetrant is then removed; a developer (typically a dry powder) is then applied to the surface, to draw out the penetrant in the crack and produce a surface indication. Cracks as narrow as 150 nanometres can be detected. The indications produced are much broader than the actual flaw and are therefore more easily visible. Liquid penetrant testing can be applied to any non-porous clean material, metallic or non-metallic, but is unsuitable for dirty or very rough surfaces. Surface cleaning is a vital part of the penetrant testing technique. The method can be manual, semi-automatic or fully automated. Penetrant inspection, continuous-operation production lines in which the specimens are cleaned, dipped, washed, dried, etc on a time cycle are common. Recently, equipment to fully automate the visual inspection stage of the process, by robotic handling of the specimen on a programmed procedure with television camera viewing and pattern recognition to identify and recognise flaws, has been introduced. Television image enhancement processes can be included. A special, very high sensitivity penetrant process, using radioactive tracers is sometimes used, but requires very stringent safety procedures.

Magnetic Particle Testing (MT)

This method is used for the detection of surface and near-surface flaws in ferromagnetic materials and is primarily used for crack detection. The specimen is magnetised either locally or overall, and if the material is sound the magnetic flux is predominantly inside the material. If, however, there is a surface-breaking flaw, the magnetic field is distorted, causing local magnetic flux leakage around the flaw. This leakage flux is displayed by covering the surface with very fine iron particles applied either dry or suspended in a liquid. The particles accumulate at the regions of flux leakage, producing a build-up which can be seen visually even when the crack opening is very narrow. Thus, a crack is indicated as a line of iron powder particles on the surface. The method is applicable to all metals which can be strongly magnetised – ferritic steels and irons, but not generally austenitic steels. The method of magnetisation must produce a magnetic field with lines of force at a large angle to the expected direction of the cracks to be detected, so that it is usual to apply the magnetisation more than once in different directions, for example in two directions mutually at right-angles, but methods of swinging the field direction during magnetisation are available.

Ultrasonic Testing (UT)

Manual Ultrasonic Testing (UT) one of the more common non-destructive testing methods performed on materials. This testing utilises high frequency mechanical energy, i.e. high frequency sound waves, to conduct examinations and measurements on a test area. Typically the UT inspection system consists of a ultrasonic transducer, pulser/receiver, and display unit. A pulser/receiver is an electronic device that can produce high voltage electrical pulses to the transducer. When driven by the pulser, the transducer generates high frequency ultrasonic sound energy into the material in the form of sound waves. When there are discontinuities such as inclusions, porosity, cracks, etc. in the sound path, part of the mechanical energy will be reflected from the discontinuities' (reflectors') surface. The reflected sound waves signal received by the transducer is then transformed back into an electrical signal and its intensity is shown on the display unit. The sound waves travel time can be directly related to the distance that the signal has travelled. From the signal, information about reflector location, size, orientation and other features can be determined.

Radiographic/X-Ray Testing (RT)

Radiographic Testing (RT) is a non-destructive testing (NDT) method which uses either x-rays or gamma rays to examine the internal structure of manufactured components identifying any flaws or defects. In Radiography Testing the test-part is placed between the radiation source and film (or detector). The material density and thickness differences of the test-part will attenuate (i.e. reduce) the penetrating radiation through interaction processes involving scattering and/or absorption. The differences in absorption are then recorded on film(s) or through an electronic means. In industrial radiography there are several imaging methods available, techniques to display the final image, i.e. Film Radiography, Real Time Radiography (RTR), Computed Tomography (CT), Digital Radiography (DR), and Computed Radiography (CR).

Phased Array Ultra Sonic Testing

Phased array ultrasonic systems utilise multi-element probes, which are individually excited under computer control. By exciting each element in a controlled manner, a focused beam of ultrasound can be generated. Software enables the beam to be steered. Two and three dimensional views can be generated showing the sizes and locations of any flaws detected.

Time Of Flight Diffraction

In time-of-flight diffraction (ToFD) systems, a pair of ultrasonic probes are used, sitting on opposite sides of a weld-joint or area of interest. A transmitter probe emits an ultrasonic pulse which is picked up by the receiver probe on the opposite side. In an undamaged part, the signals picked up by the receiver probe are from two waves: one that travels along the surface (lateral wave) and one that reflects off the far wall (back-wall reflection). When a discontinuity such as a crack is present, there is a diffraction of the ultrasonic sound wave from the top and bottom tips of the crack. Using the measured time of flight of the pulse, the depth of the crack tips can be calculated automatically by trigonometry application. This method is even more reliable than traditional radiographic, pulse echo manual UT and automated UT weld testing methods.

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