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What Causes Stainless Steel to Rust?

There is a misconception that stainless steel never rusts or corrodes. While it does take a lot to cause corrosion or rust in stainless steel because of its natural and strong corrosive resistance, it can still happen.

How Resistant to Rust Is Stainless Steel?

The level of corrosive resistance that stainless round bars or other stainless steel products will have is directly determined by their chromium content. Stainless steel contains a minimum chromium content of 10.5% (source). When chromium and oxygen interact with one another, that creates a substance known as chromium oxide. This becomes a film over the stainless steel that behaves passively but is attracted to electrons. It will stick to the surface of the stainless steel and then prevent corrosion an create a barrier that keeps out oxygen and liquid from getting into the interior of the steel and damaging it. In other words, the chromium oxide is responsible for giving stainless steel its rust resistant qualities.

How Rust Can Affect Stainless Steel

It is possible for your stainless concentric reducer or other stainless steel components to rust, given the right circumstances. This happens if the steel has been exposed to moisture, chemicals or extreme heat for a lengthy period of time. The steel will take plenty of time to corrode, so you won’t notice any corrosion right away.

How much chromium content the steel has will determine if it rusts and how long it takes to rust. The steel can be scratched and then form a new layer of chromium oxide on top to protect itself, but that does not always happen, especially if the chromium content is too low. If a new layer is not formed when the steel is damaged, then rust can start to form.

Rust can appear in different forms in the steel, including as stress corrosion, pitting, galvanic corrosion, inter-granular corrosion, and more. This weakens the steel and makes it more prone to severe damage and structural instability over time. The longer the rust remains there, the weaker the steel will become over time.

What Can Cause Stainless Steel to Rust?

Corrosion might occur after some welding has been done. This process could heat the steel so much that it weakens and allows rust to form from the carbide precipitation that the welding creates.

If stainless steel products are mixed with regular steel or a kind of iron steel, that will likely cause rust as well in the right conditions.

If there are chlorides in the area or the steel is exposed for long periods of time, it can start to rust after a while. Heating the steel up at extreme temperatures can also cause rusting, as it weakens the steel.

Anything that damages or weakens steel can open it up to rusting, if the damage is severe enough and prolonged enough. Typically, stainless steel products are incredibly durable and able to withstand severe weathering and other effects that would cause rust in lesser metals. Stainless steel is extremely durable and reliable in all conditions, so would make a great choice of metal for a whole host of different products.

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