Corrosion service includes (corrosion detection), it is very important in cultural heritage assessment. Many structures contain metal targets embedded in masonry or mortar, and corrosion can cause significant damage.
In corrosion service, the detection by non-destructive methods is difficult and highly localized, providing in most cases incomplete results. In order to obtain a more thorough analysis, ground-penetrating radar was applied and evaluated to detect corrosion damage.
This technique is a non-destructive method that covers a large area of study whereas other methods are limited to a small area or specific points. Therefore, controlled laboratory tests were designed to determine possible differences in the radars obtained for corroded and non-corroded targets.
From these analyses, it was observed that corrosion appears to increase the attenuation of the radar signal, making it difficult to detect targets near damaged bars. The results were applied to the study of mosaic roofs in Barcelona. This park is one of the most important modernist complexes in Barcelona.
It is characterized by structures with roofs and benches with tesserae structures. Some of these structures are most likely supported by metallic elements, and seepage causes significant damage observed on the tesserae structure. The objective of the study was to define the possible existence of these metallic targets, by determining their location.
And, in the case of the existence of metallic elements, to define which areas are most affected by corrosion. The results show the existence of metallic supports in many parts, as well as some defined areas that could be damaged. Call us or contact us to benefit from our new corrosion service.
What is Corrosion?
Corrosion can be defined as the destruction or deterioration of a material due to a reaction with its environment. The term can refer to a process or to the damage caused by such a process.
Causes of Corrosion
Metal corrodes when it reacts with another substance such as oxygen, hydrogen, an electric current or even dirt and bacteria. Corrosion can also occur when metals such as steel are subjected to too much stress, causing the material to crack.
The most common type of iron corrosion occurs when iron is exposed to oxygen and water, creating a red iron oxide commonly known as rust. Rust can also affect iron alloys such as steel. Iron rust can also occur when iron reacts with chloride in an oxygen-deprived environment, while green rust, which is another type of corrosion, can form directly from metallic iron or iron hydroxide.
Types of Corrosion
Uniform Corrosion: This is the most common form of corrosion, usually occurring uniformly over large areas of a material’s surface.
Pitting Corrosion: One of the most aggressive forms of corrosion, pitting corrosion can be difficult to predict, detect or characterize. This type of localized corrosion occurs when a local anodic or cathode-ray point forms a corrosion cell with the surrounding surface.
This puncture can create a hole or cavity that typically penetrates the material in a vertical direction downward from the surface.
Pitting corrosion can be caused by damage or breakage of the oxide film or a protective coating and can also be caused by non-uniformities in the metal structure. This dangerous form of corrosion can cause a structure to fail despite relatively little metal loss.
Crevice Corrosion: This form of corrosion occurs in areas where oxygen is restricted, such as under washers or bolt heads. This localized corrosion usually results from a difference in ion concentration between two areas of metal. The stagnant microenvironment prevents the flow of oxygen, which stops passivation and causes a build-up of stagnant solution that moves the pH balance away from neutrality.
The imbalance between the crevice and the rest of the material contributes to high corrosion rates. Crevice corrosion can occur at lower temperatures than pitting corrosion, but it can be minimized by proper joint design.
Inter-granular Corrosion: Inter-granular corrosion occurs when impurities are present at the grain boundaries that form during the solidification of an alloy. It can also be caused by the enrichment or depletion of an alloying element at the grain boundaries. This type of corrosion occurs along or near the grain boundaries, affecting the mechanical properties of the metal, even though most of the material is not affected.
Corrosion Cracking: Stress corrosion cracking refers to the growth of cracks due to a corrosive environment that can cause ductile metals to fail when subjected to tensile stress, especially at elevated temperatures. This type of corrosion is more common with alloys than with pure metals and is dependent on the specific chemical environment, where only small concentrations of active chemicals are needed to cause catastrophic cracking.
Galvanic Corrosion: This form of corrosion occurs when two dissimilar metals in physical or electrical contact are immersed in a common electrolyte (such as salt water) or when a metal is exposed to different concentrations of electrolyte.
When two metals are immersed together, called a galvanic couple, the more active metal (the anode) corrodes faster than the more noble metal (the cathode). The galvanic series determines which metals corrode faster, which is useful when using a sacrificial anode to protect a structure from corrosion.