For the detection of corrosion there are a number of important recommendations regarding the use of the appropriate tools and techniques.
By Juan Manuel Álvarez*
Corrosion detection can also be related to the term "inspect", i.e. finding corrosion for identification and titration purposes, but that does not involve the removal or treatment of corrosion.
To detect in time the appearance of corrosion products, these inspections must be carried out by analyzing frequencies determined by the environment, the level of protection applied and the mechanical or structural requirements and responsibilities of the materials with which the components and structures are manufactured.
For its identification and assessment, detection is carried out through non-destructive procedures. In principle, the identification of corrosion is the qualitative determination of the type of corrosion that is based on the defectology, a theme that establishes the different types of deterioration, its origin and mechanism of reaction or propagation.
On the other hand, the purpose of the valuation is to determine the level and / or degree of Corrosion that occurs in the material. This suggests making a measurement that allows to size the affectation of the material generated by the formation of the Corrosion products present during the inspection.
Visual inspection
For example, visual inspection is a non-destructive technique that allows compliance with the identification either by knowledge of the inspector and verification through the corresponding standards, as well as with the use of comparators that help identify the type of Corrosion present.
Within the inspection, the direct visual is understood as the remote visual; the first of these is done with the help of equipment or instruments such as borescopes, videoscopes and flexoscopes. The above equipment or instruments allow visual inspection to be carried out in areas or areas where there is no access for direct visual inspection, using probes that run through the interiors of pipes and structures to show the inspector the internal condition of the surface of the materials and thus perform the corrosion inspection for detection and identification.
Other non-destructive inspection techniques that allow the detection of Corrosion are:
- Eddy Currents. It uses the principle of surface conductivity of the material, with the presence of corrosion products varies the conductivity reporting the presence of deterioration.
- Radiography. The concept of differential absorption of penetrating radiation is used, which in the negatoscope will be observed in a shade of gray different from the rest of the material without the presence of corrosion products.
- Ultrasound. It uses the speed of sound in materials, which allows it to detect the presence of corrosion products due to the effect of the change in density at the same frequency.
For the correct selection of the technique and tool for the detection of Corrosion must be taken into account:
- Access to the surface to be inspected.
- The properties of the material.
- The geometry of the part, component or structure to be inspected.
- The luminosity at the time of inspection.
- The surface condition of the material.
- The presence of materials that may interfere with the inspection (painting, for example).
In addition to the above, the reliability of the equipment or tools to be used must be verified through calibration and when necessary of the standards to be used for calibration.
Absolutely always, for any inspection, in any technique, the cleaning of the area or area to be inspected must be carried out.
Inspections for the detection of Corrosion must be based on the reliability offered by the material, so that it can satisfactorily fulfill its function within structural safety margins.
Note: The following article will cover the topic "Procedures and standards related to Ageing".
As always I wish you a good aging and many successes in your work.
* Juan Manuel Álvarez Rodríguez. Designer for Corrosion Control, Certified Coating Inspector, Corrosion Technician and Marine Coating Inspector (NACE International, the Corrosion Society). A.S.T.M. member of the committees of corrosion, paints and coatings, fuels, general aviation, adhesives, nondestructive testing and composites. Certified Instructor ICAO (Organizacion de la Aviation Civil Internacional). Inspector in Non-Destructive Testing. Instructor, lecturer and columnist in Paints and Corrosion Specialist in Metal Structures and Composite Materials.
Juancorrosion.com [email protected]
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