The field of NDT (nondestructive testing) and assessment is varied. There are different approaches that are readily available for usage in airplane maintenance. The efficiency of any specific approach of NDT assessment relies on the skill, experience and training of the persons using the process. Each process is restricted in its effectiveness as an evaluation tool through its adaptability to the part to be inspected. It is typically required to speak with the aircraft or product maker for particular guidelines concerning NDT examination of their item.

Visual examination

ASSESSMENT BY AMPLIFYING GLASS AFTER WELDING. Cautious evaluation of all joints with a medium-power magnifying glass (a minimum of 10-power), after first eliminating all scale, is considered an appropriate technique of assessment for fixed structures. The practice of filling steel tubular structures with hot linseed or petroleum base oils, under pressure, in order to coat the within surface and inhibit corrosion, assists in the detection of weld fractures, as the hot oil will leak through fractures unnoticeable to the eye. This practice, though not understandable in all cases, is recommended where a large part of the structure has actually been rewelded by aerospace engineers.

Magnetic particle assessment

Magnetic particle inspection can be utilized only on magnetic materials; i.e., iron and steel. Most stainless or high chromium nickel and manganese alloy steels, being nonmagnetic, can not be checked by this technique. The approach consists basically of detection of discontinuities (fractures, voids, problems, pits, subsurface holes, etc.) by means of build-up of magnetic particles on the discontinuities when the part has been magnetized. The magnetic particles are used either dry as a powder or suspended in light oil. For complete magnetic inspection, both circular and longitudinal, magnetization needs to be deployed. Improper operation of Magnaflux equipment, because of defective devices or by untrained persons, can endanger the airworthiness of parts being checked. Minute electrical arc burns caused during examination, can lead to eventual failure of the part.

Circular magnetization is produced by transmitting an electrical current straight through the short article being evaluated, or through a central conductor positioned through the part, in which case, flaws parallel to the circulation of current may be identified. As an example, circular magnetization of a round steel bar would be produced by placing completions of the steel bar between the heads of the magnetic inspection machine and passing a current through the bars. Magnetic particles applied either during or after passage of the present, or after passage of the existing in magnetically absorbent steels, would divulge discontinuities parallel to the axis of the bar.Longitudinal magnetization is induced in a part by putting the part in a strong electromagnetic field, such as the center of a coil. Therefore, longitudinal magnetization of a round steel bar would be produced by placing completions of the bar in between the heads of a magnetic-inspection machine and placing the D.C. solenoid around the bar. After application of the magnetic particles, either throughout or subsequent to magnetization, discontinuities perpendicular to the axis of the bar would be divulged.

Red, black, and often grey particles are used in the wet or dry approaches. In the case of wet evaluation, a fluorescent magnetic particle might likewise be utilized. Articles examined are illuminated by so-called black light, and the magnetic particles radiance by florescence triggering any problems or indications to be easily visible. The damp examination treatment provides much better control and standardiza tion of the concentration of magnetic particles, much easier application to complicated shapes, and indicators that are simpler to analyze. This is because of the difficulty of acquiring effective distribution of the dry powder throughout magnetization. The dry procedure is especially suitable for discovering subsurface defects, such as, when checking heavy welds, forgings, castings, etc. The damp continuous procedure is recommended by aerospace engineers for many aircraft work.

The presence of build-ups of magnetic particles in magnetic examination does not necessarily mean that a defect exists. Changes in section of the part, particularly where the modification in section is very sharp, and also holes drilled through a part, will often trigger signs ( Surface area problems are most easily spotted, nevertheless, considering that a fracture will trigger a sharp line of magnetic particles to appear. Subsurface flaws are less easily found, just a basic collection of magnetic particles will be observed.

After magnetic inspection thoroughly demagnetize and clean up the parts. Take a look at for possible proof of electrical arc burns that may have taken place throughout assessment. All metal particles must be eliminated and the serviceable bits covered with an appropriate preservative.

In house NDT

Portable type magnetic particle inspection equipment has been established for usage in the detection of surface or minor surface discontinuities in ferromagnetic aircraft materials and parts. This type of devices normally offers much better results when the damp pension kind of indicator, such as that complying with Spec MIL-I-6868, is used with the powder provided by the equipment maker.

X-ray or radiographic examination might may be used on either magnetic or nonmagnetic materials for discovering subsurface voids such as open cracks, blowholes, and so on. When a photographic film or plate is used to record the X-ray (in a similar way to exposing a photographic film), the procedure is called radiography. When the X-rays are projected through the part onto a fluorescent screen, the process is referred to as fluoroscopy. The strategy used for radiography ought to can suggesting the presence of defects having a dimension parallel to the X-ray beam of 3 percent of the density of the part being radiographed for magnesium alloys, and 2 percent for all other metals and alloys. Assessment using a fluoroscopic screen is much less delicate. As a result, the radiographic method is generally utilized for assessment and the fluoroscopic method is used for culling.


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