Why 304 Stainless Steel Pipes Rust and the Principles of Rust Prevention

The Principle of Rust Prevention in Stainless Steel

304 stainless steel pipes are very common in our daily lives. However, we sometimes observe rust on stainless steel pipes. Why does "stainless" steel rust?

The traditional rust prevention method involves forming a tight protective film on the surface of stainless steel. This protective film's purpose is to prevent air from contacting the stainless steel surface, thereby preventing oxidation. The chemical rust prevention principle of stainless steel involves the transformation of the chromium-depleted layer into a chromium-rich layer under the action of stainless steel passivation solution, forming a layer of chromium trioxide on the surface, achieving excellent rust resistance.

Why 304 Stainless Steel Pipes Rust

304 stainless steel pipes are not completely rust-proof. The chromium-rich oxide film (protective film) on the surface resists atmospheric oxidation and corrosion in acidic, alkaline, and salty environments.

The corrosion resistance varies with the chemical composition of the steel, the processing state, usage conditions, and the type of environmental medium. When the protective film is damaged, rust naturally occurs.

Common reasons for the protective film on the surface of pipes being damaged in daily life include:

The surface adheres to organic substances (such as vegetable juice or noodle soup), forming organic acids in the presence of water and oxygen, which can corrode the surface over time.

The surface adheres to substances containing acids, bases, or salts (such as alkaline water or lime water from wall decorations), causing localized corrosion.

The surface contains dust or particles of other metal elements, and in humid air, the condensate between the adherent and the stainless steel pipe forms a "micro battery," causing an electrochemical reaction that damages the protective film.

Methods for Preventing Rust on Stainless Steel

The most commonly used and effective physical method is to apply anti-rust oil.

A more professional chemical rust prevention method involves using stainless steel passivation solution. This solution reacts with the pipe surface to form a dense passivation film of chromium trioxide, thereby achieving rust prevention.