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RT - Radiographic Discontinuities Part 4

RT - Radiographic Discontinuities Part 4











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Penetrant Testing (PT)

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Penetrant Testing (PT) In general terms, penetrant testing reveals surface discontinuities by the bleedout of a penetrating medium against a contrasting colored background. This is accomplished by applying a penetrant (usually liquid) to the cleaned surface of the test piece. Once this penetrant is allowed to remain on the surface for a prescribed time (dwell time), it will be drawn into any surface opening by capillary action. Subsequent removal of excess penetrant and application of a developer draws remaining penetrant from discontinuities.  The resultant indications are shown in high contrast and magnify the presence of the discontinuity so it can be visually interpreted. There are two primary ways in which penetrant materials are grouped: specifically, the type of indication produced, and the method of excess penetrant removal.  The two penetrant indications are visible and fluorescent.  The visible dye (usually red) produces a vivid red indi...
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Magnetic Particle Testing (MT)

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Magnetic Particle Testing (MT) This particular nondestructive test method is used primarily to discover surface discontinuities in ferromagnetic materials.  While indications can be observed from subsurface discontinuities very near the surface, they are very difficult to interpret, and often require testing by other methods.  Other NDE techniques are usually required for subsurface discontinuity detection and interpretation.  However, surface discontinuities present in a magnetized part will cause the applied magnetic field to create “poles” of opposite sign on either side of the discontinuity, creating a very attractive force for iron particles.  If iron particles, which are “magnetic particles” since they can become magnetized, are spnnkled on this surface, they will be held in place by this attractive field to produce an accumulation of iron particles and a visual indication of the discontinuity. While several different types of magnetic parti...
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Nondestructive Testing (NDT)

Nondestructive Testing (NDT) One of the purposes of an effective quality control program is to determine the suitability of a given base metal or a weld to perform its intended service. One way to judge that suitability is to subject the base metal or weld to destructive tests which would provide information about the performance of that test object. The major disadvantage of such an approach is that, as the name implies, the test object is destroyed in the process. Therefore, a number of tests have been developed to provide an indication of the acceptability of the test object without rendering it unusable for service. These various tests are referred to as nandestructìve tests, because they permit the nondestructive evaluation (NDE) of the metal or component. Even the destructive testing of a given percentage of parts can be expensive and assumes that the untested parts are of the same quality as those tested. Nondestructive tests yield indirect, yet still valid, results...
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