Rust on Stainless Steel: Why Does It Happen and How to Prevent It?
Stainless steel, as its name suggests, is a material known for its resistance to rust. However, this does not mean that stainless steel will not rust under any circumstances. So why does stainless steel rust and what can be done to prevent this problem? In this blog, we will discuss in detail the causes of rust in stainless steel and the solutions.
Why Does Stainless Steel Rust?
Stainless steel is resistant to corrosion thanks to its chromium (Cr) content. Chromium forms a thin oxide layer (passive layer) on the surface of the steel, which protects the material. However, in some cases, this protective layer can be damaged and rust can begin. Here are the main causes of rust in stainless steel:
- Chromium Deficiency or Wrong Alloy Selection
- The corrosion resistance of stainless steel depends on a chromium content of at least .5. Lower chromium content prevents the formation of the passive layer.
- Wrong alloy selection (for example, using a type that is not resistant to seawater) can lead to rust.
- Chloride and Salt Environments
- Chloride ions (sea water, salt air, cleaning chemicals) weaken the passive layer and cause the steel to rust. This is especially common in grade 304 stainless steel.
- Mechanical Damage or Scratches
- Scratches or damages on the surface of the steel disrupt the integrity of the passive layer and pave the way for corrosion to begin.
- High Temperature and Humidity
- Humid and hot environments increase the risk of rust. This is especially common in industrial facilities.
- Pollution and Foreign Matter Accumulation
- Dust, oil or other dirt accumulated on the surface can inhibit the function of the passive layer.
Types of Rust in Stainless Steel
- General Corrosion: Rust is seen on the entire surface. This situation usually occurs due to wrong alloy selection or excessively acidic environments.
- Pitting Corrosion: It starts as small holes on the surface and deepens over time. It is common in environments containing chloride.
- Crevice Corrosion: Occurs due to lack of oxygen at cracks or joints.
- Galvanic Corrosion: It occurs as a result of using different metals together.
Rust Prevention Methods
- Choosing the Right Material
- Choose the type of stainless steel that is appropriate for the ambient conditions. For example, 316L grade steel should be preferred in structures that will be exposed to sea water.
- Regular Cleaning and Maintenance
- Clean the surface regularly with dirt, oil and foreign matter. You can use mild soapy water or special stainless steel cleaners.
- Surface Coatings
- Apply anti-corrosion coatings (e.g. passivation treatment) to strengthen the passive layer.
- Preventing Mechanical Damage
- Be careful during assembly and handling to avoid scratches and damage.
- Corrosion Preventive Chemicals
- Reduce the risk of rust by using corrosion inhibitors, especially in industrial environments.
Stainless Steel Cleaning Tips
- Light Rust Stains: You can clean it with vinegar or lemon juice.
- Stubborn Stains: Use special stainless steel cleaners or baking soda paste.
- Scratches:Smooth the surface with sandpaper (fine grain) or stainless steel polish.
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