The 8 most common types of corrosion

Corrosion can significantly affect the service life of systems - especially if it remains undetected. In this article, you will learn more about the 8 most common types of corrosion and how modern drone technologies are revolutionising inspection in hard-to-reach areas.

How drones efficiently monitor corrosion in hard-to-reach places

Corrosion is an insidious but often underestimated enemy of industrial plants and structures. It becomes particularly problematic when it occurs in places that are difficult to access or dangerous, such as on tank ceilings, in pipes or in underwater areas. Traditional inspection methods are often complicated, time-consuming and dangerous. Thanks to modern drone technologies, such as the Elios 3 and Underwater dronesHowever, it is possible to inspect these hidden corrosion spots quickly and accurately. In this article, we look at 8 types of corrosion that you can detect safely and efficiently using drones.

1. surface corrosion

Surface corrosion, also known as uniform corrosion, is the most widespread form. It occurs evenly over the entire surface of the metal, resulting in uniform material removal. This type of corrosion is easy to recognise as the entire surface is affected and typically appears rusty or dull.

Examples:

Rust formation on steel outdoors
Corrosion on metal panelling or pipes

Protective measures:

Protective coatings such as paint or galvanic coatings
Use of corrosion-resistant materials such as stainless steel

2. pitting corrosion (pitting)

Pitting corrosion is one of the most dangerous types of corrosion as it is difficult to detect and can quickly lead to structural damage. It is characterised by small, punctual holes that penetrate deep into the material and weaken it. This type of corrosion often occurs in materials such as stainless steel when the protective film on the surface is damaged.

Examples:

Stainless steel in chloride-containing environments (e.g. in swimming pools)
Marine environments in which salt water has an aggressive effect on metal

Protective measures:

Use of protective coatings
Cathodic protection (e.g. sacrificial anodes)
Regular inspections for early detection

3. crevice corrosion

Crevice corrosion occurs in narrow gaps or under seals and screw connections where the flow of oxygen is restricted. These oxygen-poor conditions promote corrosion as aggressive chemical compounds such as chlorides accumulate and attack the material. Corrosion can progress rapidly in these small gaps and cause considerable damage.

Examples:

Screw connections on pipework
Overlaps in metal connections

Protective measures:

Avoidance of narrow gaps in constructions
Use of corrosion-resistant materials
Regular cleaning and maintenance

4. intergranular corrosion

In the case of intercrystalline corrosion, the metal decomposes along the grain boundaries, which are often more susceptible than the grain material itself. This type of corrosion often occurs after inadequate heat treatment, when carbon precipitates at the grain boundaries and leads to corrosion there.

Examples:

Incorrectly heat-treated stainless steel
Aluminium alloys in corrosive environments

Protective measures:

Control of heat treatment during production
Use of corrosion-resistant alloys
Heat treatment to reduce the carbon content

5. stress corrosion cracking

Stress corrosion cracking is caused by the interaction of mechanical stresses and a corrosive environment. This combination leads to fine cracks in the material, which in the worst case can lead to a sudden and catastrophic failure of the structure. This type of corrosion particularly affects highly stressed components such as pressure vessels and pipes. Druckbehälter und Rohre.

Examples:

Pressurised containers and pipelines that are live
Components in chemically aggressive environments, such as refineries

Protective measures:

Reduction of mechanical stresses in the design
Use of stress-free materials
Application of coatings or corrosion protection systems

6 Galvanic corrosion

Galvanic corrosion occurs when two different metals come into contact with each other in an electrolyte. The less noble metal corrodes more, while the more noble metal remains protected. This type of corrosion often occurs in humid or marine environments and can be exacerbated by the choice of unsuitable materials.

Examples:

Combining aluminium and steel in a maritime environment
Copper pipes with galvanised steel joints

Protective measures:

Avoidance of direct contact between different metals
Use of insulating materials between the metals
Use of sacrificial anodes to control the galvanic reaction

7. microbially induced corrosion (MIC)

Mikrobiell induzierte Korrosion wird durch Mikroorganismen verursacht, die in bestimmten Umgebungen wachsen und ihre Stoffwechselprodukte als Säuren oder Sulfide abgeben. Diese Substanzen fördern die Korrosion, insbesondere an schwer zugänglichen oder feuchten Stellen. MIC tritt häufig in Pipelines, Tanks und in der maritimen Industrie auf.

Examples:

Pipelines in the oil and gas industry
Ship structures that lie in seawater

Protective measures:

Regular cleaning and disinfection of systems
Use of biocides to control microorganisms
Use of antibacterial materials or coatings

8. erosion corrosion

Erosion corrosion occurs when the material is removed by a combination of mechanical wear and chemical corrosion. This often occurs in pipes or pumps where high flow velocities occur and the material is attacked.

Examples:

Turbine blades in hydropower plants
Pipes that transport liquids at high speeds

Protective measures:

Use of abrasion and corrosion-resistant materials
Reduction of the flow velocity in systems
Optimisation of the design to minimise turbulence

Conclusion

Corrosion is a complex and multifaceted problem that can affect various materials and structures. The selection of suitable protective measures requires an in-depth understanding of the corrosion mechanisms and the specific environmental conditions. By using preventive measures, suitable materials and modern inspection technologies such as drones and ROVs, corrosion damage can be recognised early and contained before major damage occurs. If you are looking for more information on the subject of corrosion, we recommend the book "Principles of Corrosion Engineering and Corrosion Control" by Zaki Ahmad to the heart.