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NonDestructive Testing

Nondestructive testing asks "Is there something wrong with this material?" Various performance and proof tests, in contrast, ask "Does this component work?" This is the reason that it is not considered nondestructive testing when an inspector checks a circuit by running electric current through it. Hydrostatic pressure testing is usually proof testing and intrinsically not nondestructive testing. Acoustic emission testing used to monitor changes in a pressure vessel's integrity during hydrostatic testing is nondestructive testing.

Another gray area that invites various interpretations in defining nondestructive testing is that of future usefulness. Some material investigations involve taking a sample of the inspected part for testing that is inherently destructive. A noncritical part of a pressure vessel may be scraped or shaved to get a sample for electron microscopy, for example. Although future usefulness of the vessel is not impaired by the loss of material, the procedure is inherently destructive and the shaving itself - in one sense the true "test object" - has been removed from service permanently.

The idea of future usefulness is relevant to the quality control practice of sampling. Sampling (that is, the use of less than 100 percent inspection to draw inferences about the unsampled lots) is nondestructive testing if the tested sample is returned to service. If the steel is tested to verify the alloy in some bolts that can then be returned to service, then the test is nondestructive. In contrast, even if spectroscopy used in the chemical testing of many fluids is inherently nondestructive, the process is destructive if the test samples are discarded after testing.

Hardness testing by indentation provides an interesting test case for the definition of nondestructive testing. Hardness testing machines look somewhat like drill presses. The applied force is controlled as the bit is lowered to make a small dent in the surface of the test piece. Then the diameter or depth of the dent is measured. The force applied is correlated with the dent size to provide a measurement of surface hardness. The future usefulness of the test piece is not impaired, except in rare cases when a high degree of surface quality is important. However, because the piece's contour is altered, the test is rarely considered nondestructive. A nondestructive alternative to this hardness test could be the use of electromagnetic nondestructive testing.

Radiographic Testing

Radiography is the best method for detecting volumetric flaws. It is commonly applied in the inspection of shrink, inclusions and porosity. It is also used to investigate welded joints for lack of penetration voids and heat affected zone cracking.

Ultrasonic Testing

Ultrasonic testing is a method that detects internal and surface flaws. It can detect inclusions in steel such as silicate and sulfide. It can find cracks which can occur in production and in service by fatigue. It can discover other flaws such as pipe, shrink and porosity which are common in casting applications. In addition to these flaw detection capabilities, ultrasonic testing can also measure physical parameters such as density, thickness and elastic modules.

Magnetic particle Testing

Magnetic particle testing is applied to alloys. It is most commonly used for inspecting extrusions, castings and forgings, heat treatment, machining and polishing. It is the method that decides defects visually by shapess which magnetic particles are attracted and formed when applying magnetic particle to test object,
magnetizing by Ac or Dc.

Liquid Penetrant Testing

Liquid penetrant testing is a method used to detect surface flaws on large surface areas. It is very time consuming, economical and can be applied to a large number of components and materials. It can also be used to reveal surface connected flaws.

Eddy Current Testing

Eddy current testing is especially designed to test nonmagnetic Tube, which provides useful information to decide the time of estimating remnant life, deterioration, repairing, replacement and so on by detecting defects such as corrosion, erosion, dent, pin hole, material changing which happen to internal and external side of tube for Condenser, Heat Exchanger.

Leak Test

Leak testing is a method reveals the defects by the flow of gas or liquid in or out of the test specimen. The presence of leaks can be presented by water or gas seepage, or by change in pressure. It is used for inspecting vessels, storage tanks and pipeline.