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Non-Destructive Testing with Qualified Personnel

Non-Destructive Testing (NDT), or Non-Destructive Evaluation (NDE), comprises a set of inspections, tests, and surveys conducted using methods that do not alter the material under examination and do not require the destruction or sampling of specimens for subsequent analysis. The fundamental characteristic of these types of inspections is the ability to verify structural details, even on a small scale, without any alterations or interference with the material being examined. Non-Destructive Testing (NDT) methods, therefore, represent an extremely important tool for inspecting various types of industrial infrastructure and transportation systems, both public and private. Security Control started operating in 1980 with qualified and certified personnel according to the American standard SNT-TC-1A. Since 1988, the personnel has been qualified by the ACCREDIA body.

Currently, SECURITY CONTROL relies on personnel certified at levels 1, 2, and 3 in the following methods:
MRT magnetic inductive testing of wire ropes;
MT Magnetic particle testing in the general sector;
PT Liquid penetrant testing in the general sector;
UTUltrasonic testing of forgings, stampings, castings;
VT Visual inspection on both new or in-service parts, as well as on ropes and accessories for anchoring, harnessing, lifting, and transporting loads.

Principle

The magnetic-inductive method exploits the ferromagnetic properties of steel, the material used for ropes in industrial plant engineering and public and private transportation sectors.

The method involves magnetizing the section of rope to be inspected with a longitudinal magnetic field of sufficient intensity to saturate the steel of the rope. Around the rope, due to saturation, a magnetic flux is created in the air parallel to the rope’s field.

If the rope, in a section, has internal or external inhomogeneities, the flux lines around the anomalies lose linearity due to the variation in metal section. By moving a coil longitudinally in the field, induced electromotive forces occur at the inhomogeneities. Once amplified, these forces can be sent to graphical or computerized recording devices. From a practical standpoint, to achieve this effect and conduct effective testing, suitable tools are used. These tools are movable along the rope and capable of magnetizing the rope uniformly with a longitudinal field along its entire length. These tools, called detectors, currently use permanent magnets, which allow for greater versatility and ease of use. They don’t require on-site electrical power, are quick to install and transport, and are easy to maintain.

Application

This method can be optimally used on the majority of ropes in operation, both in public and private transport systems, as well as in construction and industrial plants.

The magnetic inductive method is particularly suitable for detecting defects that arise due to the type of environment and operating conditions. With this method, it’s possible to assess the overall condition of the rope and identify any breakages in the wires, including internal ones, which can lead to a loss in efficiency and safety characteristics of the systems.

The instruments are entirely designed and manufactured in SECURITY CONTROL’s laboratories and can be customized for specific control requirements.

Principle

The technique exploits a particular characteristic of ferrous alloys: ferromagnetism, which is the ability to concentrate a magnetic field in the presence of discontinuities on the surface of the test piece.

In the vicinity of a discontinuity, such as a crack, the magnetic field lines locally deviate and create a magnetic field anomaly at the edges of the defect.

If the defect is surface-breaking or subsurface, some of the magnetic field lines are dispersed beyond the surface.

To highlight the defect, it is sufficient to spray the surface with special ferromagnetic powders, which can be colored or fluorescent. The particles will concentrate, aligning themselves along the lines of magnetic flux.

Application

Magnetic particle testing is particularly suitable for detecting surface and subsurface defects such as cracks, inclusions, and folds, but it is not effective for internal defects. The sensitivity in detecting rounded defects is also quite low. The minimum detectable defect size mainly depends on its distance from the surface, and in any case, the analysis capability is better and faster compared to the liquid penetrant method. SECURITY CONTROL carries out inspections directly on-site using a portable testing device.

Principle

This non-destructive test exploits the ability of certain liquids to penetrate, through capillarity (and not gravity), into surface defects (cracks, voids, etc.). The low surface tension of these liquids, as well as their remarkable permeation capacity, ensure penetration even into extremely thin discontinuities.

After the application and penetration of the liquid (called penetrant), which requires a variable amount of time depending on the type of product used, the material to be inspected, and the type of discontinuity to be detected, excess penetrant is removed from the surface by washing with cold running water.

Since water has a higher surface tension compared to the penetrant liquid, it is unable to remove the liquid from the cracks into which it has penetrated by capillarity.

After washing, once again utilizing the principle of capillarity, the remaining penetrant liquid inside the anomalies is extracted using a developer liquid. The penetrant liquid, “climbing” by capillarity, will leave a signal in the developer much larger in size than the defect that generated it. Depending on the technique applied, the defect can be highlighted in various ways: either as a red-colored stain or as a fluorescent stain easily detectable by irradiation in the dark with a Wood lamp.

The method is not without its difficulties, especially in the defect evaluation phase, as sometimes mechanical processes result in “defect indications” that can only be resolved by a particularly experienced operator.

 

Application

Inspection with liquid penetrants is a method particularly suitable for highlighting and locating surface discontinuities, such as cracks, porosity, and folds, quickly, economically, and with great accuracy.

Contrary to magnetic inspections, liquid penetrants can be successfully applied to any component, regardless of its geometry or material (except for porous pieces or those with particularly rough surfaces).

Principle

The defect detection method using ultrasonics is a technological application of the echo phenomenon. It is generated by the reflection of sound waves bouncing off the surface of an obstacle and returning to the listener’s ear. In ultrasonic testing, waves (ultrasonic and therefore not audible to the human ear) are generated using the piezoelectric properties of certain materials. These properties consist of the ability of materials to contract and expand when subjected to an electric field. If the generated field has the appropriate frequency, the material’s vibrations will produce ultrasonic elastic waves. The phenomenon is reversible. In other words, the same material capable of emitting ultrasonic waves can generate an electrical signal when struck by a beam of elastic waves. The ultrasonic waves sent into the material to be examined propagate with the same frequency as the generator and at a velocity that depends on the material being traversed. When the beam encounters an obstacle, it will be reflected, absorbed, deflected, or diffracted according to specific physical laws. The reflected waves take a certain time to return to the receiving probe, and this time depends on the distance to which the obstacle (reflector) is placed. By analyzing the time taken based on the specific velocity of the material, one can determine its position.

The energy absorbed by the defect, struck by the incident waves, causes it to vibrate, emitting elastic waves in turn. The signal returning to the transducer contains all the information about the dimensions, geometry, and nature of the obstacle encountered by the incident ultrasound beam. As mentioned, the physical phenomenon of piezoelectricity is reversible: when the reflected or emitted wave from the obstacle returns back to the generating transducer, it will generate an electrical signal which, once appropriately amplified and filtered, can be displayed on an oscilloscope.

Application

Ultrasonic testing can be considered complementary to magnetic particle testing (or liquid penetrant testing) as it also reveals internal defects. Ultrasonic testing finds wide application in inspecting welds, castings, detecting inclusions in rolled products, and is used for thickness measurement. The inspection is carried out by technicians from SECURITY CONTROL directly on structures in large naval and industrial plants, as well as within public and private transportation systems.

Visual Inspection refers to the inspection of objects performed with the naked eye or using aids such as lenses and endoscopes. The interpretation and evaluation of the indications detected are carried out by the operator based on specific parameters regarding the acceptability of defects in the inspected artifact. Therefore, it is evident how the technical expertise of the personnel combined with accumulated experience are essential factors to ensure the sensitivity and reliability of the result. The examination is termed direct when it is possible to inspect the object with the naked eye, under appropriate lighting and viewing conditions. The examination is instead remote when direct access to the surface to be examined is not possible, requiring the use of equipment such as mirrors, endoscopes, cameras, etc. It is necessary for the resolution provided by such instruments to be at least equivalent to that of the human eye. Dimensional inspections are closely related to the quality control of manufacturing companies. They allow for inspections on prototypes or samples during production, all the way to the finished product. Dimensional inspections aim to ensure that the final outcome matches what is specified in the technical drawing in terms of shape, dimensions, and geometries.

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