Non Destructive Testing
What is NDT?
Non destructive testing is a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage. NDT is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research.
Where is NDT used?
Nondestructive testing methods are routinely applied in industries where a failure of a component would cause significant hazard or economic loss, such as in transportation, pressure vessels, building structures, piping, and hoisting equipment.
What are NDT methods?
NDT methods rely upon use of electromagnetic radiation, sound and other signal conversions to examine a wide variety of articles for integrity, composition, or condition with no alteration of the article undergoing examination. Visual inspection (VT) is often enhanced by the use of magnification, borescopes, cameras, etc for direct or remote viewing.
Eddy current testing
Eddy current testing uses the principle of electromagnetic induction to detect flaws in conductive materials. An excitation coil carrying current is placed in proximity to the component to be inspected. The coil generates a changing magnetic field using an alternating current, which interacts with the component generating eddy currents.
Variations in the phase and magnitude of these currents are monitored either by using a second coil, or by measuring changes to the current flowing in the excitation coil. The presence of any flaw will cause a change in the eddy current field and a corresponding change in the phase and amplitude of the measured signal. In the case of nondestructive testing (NDT), these are displayed on an eddy current flaw detector as a distinct change in signal.
Liquid penetrant inspection (LPI), or penetrant testing (PT), this is a low-cost inspection method widely used to locate surface-breaking defects in non-porous materials (metals, plastics, ceramics). LPI is used to detect casting, forging, and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.
DPI uses capillary action where a low-surface-tension fluid penetrates into clean and dry surface-breaking flaws. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed and a developer is applied to draw penetrant from flaws, making indications visible
Magnetic particle testing
Magnetic particle testing (MT) is a non-destructive testing technique utilized to detect defects or discontinuities (such as cracks) at or near the surface in ferromagnetic metals such as iron, steel, nickel, cobalt, etc. Magnetic particle testing (as well as other non-destructive testing techniques) is primarily utilized in the industrial sector to test metal materials such as oil & gas pipelines and various metal machinery components to prevent failures or accidents. Some of the most common industries that utilize magnetic particle testing include petrochemical, automotive, aerospace and structural steel – just to name a few. In addition, magnetic particle testing may be utilized to inspect underwater structures such as pipelines.
Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more.
A typical UT inspection system consists of several functional units, such as the pulser/receiver, transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high frequency ultrasonic energy. The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface. The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen. Signal travel time can be directly related to the distance that the signal traveled. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.