Does Stainless Steel Rust? How to Protect Stainless Steel Products from Rusting?
September 2nd, 2022
Stainless steel is one of the most versatile materials in the market. It is not affected by materials that erode iron and normal steel. This makes it popular and commonly used for being corrosion-resistant. Many people don’t know that stainless steel is not 100% impervious to corrosion. This blog will talk about does stainless steel rust and how we can protect stainless steel products from rusting.
Many things can cause stainless steel to rust and corrode. These include exposure to chemicals, heat, moisture, grease and saline. The amount of chromium present in stainless steel determines the protection level. In this blog, we are going to talk about what is stainless steel, how can it rust and steps to avoid corrosion.
Table of Contents
Chapter 1: What is Stainless Steel?
Stainless steel is a material that has gained popularity because of its nature. It is recyclable and has an almost 100% recovery rate. This is what makes it one of the most popular materials in the construction industry. Environmentally, it is inert, neutral and durable. This is what ensures life-long longevity in most cases.
The advantages just keep on adding up. It is easy maintenance, hygienic, looks good, durable, sustainable, and sturdy and is not affected much by external factors. This is why it is largely being used in many industries like transportation, energy, research, construction, logistics, food and even the health industry.
1) Definition of Stainless Steel
Steel is a compound of both carbon and iron. The difference between stainless steel and normal steel is the composition. Stainless steel has a minimum of 10.5% chromium and a maximum of 1.2% carbon. This is why it is called “stainless” as it does not rust.
When you expose stainless steel to oxygen, the chromium reacts with oxygen to form a very thin layer of chromium oxide on its surface. The layer is so thin that it can’t be seen by the naked eye. This stops the stainless steel from further oxidization.
Even if for any reason the layer of chromium oxide is scratched, it forms again. This acts as a protection layer for the stainless steel that is beneath it.
2) How is Stainless Steel different from Normal Steel?
Stainless steel and steel are alloys of iron. These are metal alloys. Out of the many differences between the two, the major difference is the property of being corrosion-resistant. Normal steel is prone to corrosion while stainless steel is not. The difference has been discussed in detail above.
Chapter 2: Different Types of Steel Corrosion
Unlike general belief, stainless steel also undergoes corrosion. Some people believe that is it corrosion-free. This is not the case. Below we are going to discuss the main six types of corrosion that can occur in stainless steel.
1) General Corrosion
Generally, corrosion in stainless steel is not uniform. In ordinary alloy and carbon steels, corrosion occurs uniformly. But some chemicals like acids act on the passive layer and uniformly corrode the outer layer of stainless steel. Sulphur and hydrochloric acid are very aggressive on stainless steel at specific concentrations.
This is the most common type of corrosion. It is also predictable, manageable and preventable. It occurs mostly in stainless steel that has a lower than 1 pH level.
2) Galvanic Corrosion
When two metals that are not the same come in contact with the presence of an electrolyte, a galvanic cell is made. The electrolyte can be any solution or water. This accelerates the corrosion manifold. This is also known as bimetallic corrosion. The easiest way to avoid this is to separate these metals. A non-metallic insulator like rubber is best in this case.
3) Pitting Corrosion
Other chemical species also attach to the passive layer of the outer stainless steel layer. CI – chloride ion is the chemical species that affect this layer the most. The reason is that it is mostly found in day-to-day materials like bleach and salt. This corrosion can be avoided by ensuring that the stainless steel is not exposed to these chemicals for longer periods.
4) Intergranular Corrosion
This is not a common form of stainless steel corrosion. It is very rare and does not occur much. This occurs when the carbon level is very high. When this occurs, carbon combines with this chromium and forms chromium carbide. For this, you need very high temperatures of around 450 degrees to 850 degrees C. This is known as sensitization. To avoid this, it is good to go with a form of stainless steel with niobium or titanium.
5) Stress Corrosion Cracking (SCC)
This is also a rare form of corrosion. It occurs only when there is a perfect combination of corrosive species, temperature and tensile stress. The most common corrosive species is chloride ion. This corrosion occurs mostly in swimming pools and hot water tanks.
6) Crevice Corrosion
The thin layer of corrosion that forms on the surface of stainless steel and prevents further corrosion can happen only when there is an oxygen supply. When there is no oxygen supply, the layer does not form. This leads to corrosion of the stainless steel. You can avoid this by using sealant on the crevices in air-tight spaces.
Chapter 3: How to Prevent Stainless Steel from Rusting?
Even though stainless steel is also not 100% corrosion-free, there are different methods by which you can ensure that this corrosion does not occur. Following these methods can help prevent corrosion and rust.
You can prevent corrosion during the fabrication stage. The prevention process starts so early. You have to make sure that during the process of fabrication, stainless steel does not come into contact with ordinary steel or any iron. Not even particles of carbon steel should come in contact with it to avoid contamination. If you don’t avoid this exposure in the fabrication process, it can lead to rust after the process is done.
To prevent this, you need to be very vigilant. All the tools, work tables, steel turning rolls, storage units and even the chains need to be free from any contamination. The tools that are used for grinding and cutting alloy or carbon steel should not be used for cutting stainless steel.
Another critical stage is the designing process. When stainless steel is made into different things, special care needs to be taken in the design process. Being proactive is going to be good in the long run. You need to make sure there is zero chance of contamination and an excellent air ventilation system. Moreover, water penetration needs to be zero to ensure that there is no surface damage.
Proper maintenance can also lead to fewer chances of rust forming on stainless steel. Rust is inevitable. Proper chemical and mechanical methods should be used to remove any rust formation on the things made of stainless steel. If you ignore the rust, it will build up and you can end up with a lot of rust.
4) Materials to avoid
Some materials should never be used on stainless steel. These include:
The finishing used on stainless steel also helps in the prevention of rust. If the stainless steel is going to be used in a rough environment, go for finishing with a higher grade of stainless steel. If it is not going to be used in very harsh environments, you can be for a lighter grade of stainless steel finishing.
Chapter 4: How to Remove Rust from Stainless Steel
The best thing about stainless steel is that in many cases, the rust on it can be removed. Sometimes, you might need professional help, but it is worth it. Following are the two major ways in which you can remove rust from stainless steel.
1) Acetic Acid
Acetic acid also plays a role in cleaning out rust from stainless steel. It is effective and gives accurate results. When compared to phosphoric acid, the reaction time is slower. Once you have used the acid on the rusty areas, you need to rinse the stainless steel well. Be sure that you use deionized water to perfectly remove every particle of the acid. If you leave any particle, it will only make matters worse.
2) Phosphoric Acid
Phosphoric acid helps to dissolve iron oxide only. It does not attack or affect chromium, nickel, chromium oxide and the other elements present in the steel. It is easily available everywhere and it does not even need to be diluted as it is very non-aggressive. Unfortunately, it does not work 100% and the results are not very effective.
Chapter 5: FAQs
1) Will Stainless Steel Rust?
Yes, stainless steel can rust. Even though it is largely corrosion-resistant, it can still rust under certain conditions. The level and rate at which it rusts are much less than normal steel. That is why most people believe that it can’t rust.
2) What factors affect Stainless Steel Corrosion?
Many factors can affect the corrosion of stainless steel. These include certain environmental factors, exposure to certain chemicals and general wear and tear over time.
3) What is Bimetallic Corrosion?
Bimetallic corrosion and galvanic corrosion are the same things.
4) Is it possible to save stainless steel from environmental factors?
Yes. Through proper maintenance, stainless steel can be protected from external environmental factors.
With this blog, you now know that even stainless steel is not 100% corrosion and rust-free. Even though most of the time, the thin layer of chromium carbonate formed on the outer surface (which can’t be seen with the naked eye) saves the steel from further corrosion.
With the right preventive measures, you can even increase the durability and longevity of stainless steel for years to come. If you want to know more about it, leave us a message at Ejet Sourcing and we will get right back to you!