De vanligaste korrosionsfallen
De korrosionstyper som främst kan förekomma på aluminium är:
- bimetallkorrosion (före detta galvanisk korrosion)
- gropfrätning
- spaltkorrosion
- filiformkorrosion
En annan, mer speciell korrosionstyp, är sprickbildning på grund av spänningskorrosion. Den kan förekomma främst hos höghållfasta legeringar, till exempel AlZnMg-legeringar, om dessa utsätts för stora dragspänningar under lång tid och det finns ett korrosionsmedium närvarande.
Bimetallkorrosion
Bimetallkorrosion kan uppstå när olika metaller är i metallisk kontakt med varandra, samtidigt som det finns en kontinuerlig elektrolytbrygga mellan metallerna. Figur 54 och Figur 55 visar exempel på bimetallkorrosion.
Figur 54 Den ädlaste metallen blir katod (–) och skyddas mot korrosion, medan den oädlaste blir anod (+) och korroderar. En liten katodyta och en stor anodyta ger obetydlig korrosion. I det omvända fallet kan man, i svår miljö, snabbt få allvarliga angrepp.
Figur 55 Elektrolytisk cell mellan aluminium och koppar. Den oädlaste metallen (här aluminium) blir anod och korroderar.
I de flesta kombinationer med andra metaller är aluminium den oädlare. Därför
How to Effectively Recognize, Prevent and Treat Pitting Corrosion
Pitting corrosion initially presents itself as one or more tiny holes or cavities that are nearly invisible to the human eye. But this type of corrosion can quickly progress in both horizontal and vertical directions below the substrate's surface, and can result in failures and breakdowns with disastrous consequences. Some of the deadly bridge collapses in history are attributed to the onset of deep or wide cavities as a result of pitting.
A structural member (e.g., a metal beam) can lose its load bearing capacity due to pitting corrosion, resulting in fatigue cracks due to overloading, and finally culminate in the collapse of the entire structure.
Pitting can often cause severe problems even though it is sometimes neglected by those who are responsible for the maintenance of plant equipment. (For a deep dive into one particular industry where pitting is problematic, read Pitting Corrosion in Oil and Gas Wells and Pipelines.)
For these reasons it is necessary to understand:
- The causative factors of pitting
- How to recognize when pitting occurs
- Preventive measures needed to be put in place
Types of Me
Aluminium Corrosion &#; Its Different Types
Aluminium is the second most abundant metal on earth and due to its excellent properties, is one of the most widely used metals today. Therefore, it is useful to be aware of the conditions that shorten the lifetime of these metals.
Corrosion of any metal can significantly impact its functional strength causing structural damage like cracks, partial fracture, and total material failure in extreme cases. In this article, we shall take an in-depth look into aluminium corrosion to help understand the different types of corrosion that can affect the metal.
What is Aluminium Corrosion?
Aluminium corrosion is the gradual decay of aluminium molecules into its oxides that degrades its physical and chemical properties.
By nature, aluminium is a reactive metal but it is also a passive metal.
It means that while nascent aluminium will react with oxygen and water in the environment, the resulting compound will form a layer on the surface protecting the material underneath from further corrosion. This non-reactive oxide layer sticks well to the surface and does not flake off easily, similarly to stainless steel.
Unlike deliberate processe
Uncover the risks and prevention methods for galvanic corrosion in aluminium. Learn about how different metals interact and the impact on structural integrity.
Naturally resistant to corrosion
It is known that the resistance of aluminum and aluminium alloys to normal environmental conditions is very high. The main source of protection against corrosion is a durable, self-healing oxide film, which is always present on aluminium in the surrounding air atmosphere (Fig. 1).
Figure 1 &#; Surface oxide film is a natural protection of aluminium from corrosion [1]
Main types of aluminium corrosion
There are many types of corrosion. The most coomom types are [1]:
- General
- Crevice
- Poultice
- Fretting
- Stress
- Galvanic
- Pitting
- Intergranular
The most common design error
The most common design errors in aluminum structures are related to galvanic corrosion. Galvanic or electrochemical corrosion occurs when two dissimilar metals form an electrical circuit that is completed by a liquid or film electrolyte or corrosive medium. Under these conditions, the potential difference between dissimilar metals creates an electric current passing through the electrolyte, which (current) leads
.
Aluminium Corrosion &#; Its Different Types
Aluminium is the second most abundant metal on earth and due to its excellent properties, is one of the most widely used metals today. Therefore, it is useful to be aware of the conditions that shorten the lifetime of these metals.
Corrosion of any metal can significantly impact its functional strength causing structural damage like cracks, partial fracture, and total material failure in extreme cases. In this article, we shall take an in-depth look into aluminium corrosion to help understand the different types of corrosion that can affect the metal.
What is Aluminium Corrosion?
Aluminium corrosion is the gradual decay of aluminium molecules into its oxides that degrades its physical and chemical properties.
By nature, aluminium is a reactive metal but it is also a passive metal.
It means that while nascent aluminium will react with oxygen and water in the environment, the resulting compound will form a layer on the surface protecting the material underneath from further corrosion. This non-reactive oxide layer sticks well to the surface and does not flake off easily, similarly to stainless steel.
Unlike deliberate processe
Uncover the risks and prevention methods for galvanic corrosion in aluminium. Learn about how different metals interact and the impact on structural integrity.
Naturally resistant to corrosion
It is known that the resistance of aluminum and aluminium alloys to normal environmental conditions is very high. The main source of protection against corrosion is a durable, self-healing oxide film, which is always present on aluminium in the surrounding air atmosphere (Fig. 1).
Figure 1 &#; Surface oxide film is a natural protection of aluminium from corrosion [1]
Main types of aluminium corrosion
There are many types of corrosion. The most coomom types are [1]:
- General
- Crevice
- Poultice
- Fretting
- Stress
- Galvanic
- Pitting
- Intergranular
The most common design error
The most common design errors in aluminum structures are related to galvanic corrosion. Galvanic or electrochemical corrosion occurs when two dissimilar metals form an electrical circuit that is completed by a liquid or film electrolyte or corrosive medium. Under these conditions, the potential difference between dissimilar metals creates an electric current passing through the electrolyte, which (current) leads
.