Steel Pipe Rusting And Ordinary Rusting

1. Floating Rust (Water Rust, Thin Rust, Yellow Rust)
Appearance: Light yellow or orange-yellow thin layer of powder, thinly adhering to the surface of the steel pipe, when rubbed off the yellow powder, the base remains intact without dents, pits, peeling, and the original color of the steel can be clearly seen, forming a thin yellow film in patches.

Formation Conditions

1. The oxide layer on the steel during factory rolling is damaged. In high humidity, condensation, rain, humid air environment, short-term (a few days to several tens of days) electrochemical mild oxidation occurs;
2. Large temperature differences between day and night in the warehouse cause condensation on the pipe wall, rainy season moisture return, maritime condensation water, short-term exposure to rain;
3. Only forms a thin layer of iron hydroxide, with extremely shallow corrosion depth (micron level).

2. Common rust (surface rust/deep rust, pitted rust, thick rust)

It is classified into medium rust and heavy rust.
Appearance: Red-brown or black-brown rust layer, the rust layer is thick and lumpy, peeling off and chipping off. After removing the rust layer, small pits, pockmarks and defects appear on the pipe wall, and the local wall thickness becomes thinner.

Generation conditions

1. Long-term outdoor storage, rain and sun exposure, mud and water immersion, salt/acid-base mist (coastal areas, chemical plant areas);
2. Rusting period lasts from several months to several years. Oxygen and water continuously invade for a long time, generating a thick rust composed of iron oxide and ferrous trioxide, and corroding deeper into the steel base.

(1) Removal of Floating Rust (Simple and Low Cost)
1. Dry Scrubbing / Steel Wire Brushing / Fan Wheel Grinding: Light polishing with cotton cloth or steel wire wheel can remove it completely, and the surface will be shiny after grinding;
2. High-pressure Air Blowing + Cloth Wiping, simple and efficient treatment for large quantities;
3. For mild floating rust, a weak acid rust remover (phosphate-based rust removal water) can be used for short-term soaking and wiping, then rinse with clean water and dry immediately.

> Floating rust does not require sandblasting or acid washing for long-term soaking.

(2) Removal of deep rust
1. Small scale: Use angle grinder steel wire wheel or sanding machine for grinding. In deep pits, the surface needs to be polished until the original metal color is exposed;
2. Large-scale pipes: Use shot blasting or sandblasting (the most common process in steel pipe factories);
3. Batch acid washing and passivation: Acid wash with hydrochloric acid/sulfuric acid → neutralize → rinse → dry (commonly used in anti-corrosion processing).

1. Floating Rust: Minimal impact

1. The wall thickness remains almost unchanged, and the mechanical properties (tensile strength, yield strength, pressure-bearing capacity) remain the same;
2. Only affects the adhesion of painting and galvanization: Before applying anti-corrosion treatment, the floating rust must be removed; otherwise, the paint film will peel off;
3. Seamless steel pipes, fluid pipes, and structural pipe strips with floating rust do not affect pressure-bearing or cutting and processing.

2. Severe Rusting: Significant impact, by scenario

1. 1. Pressure-bearing steel pipes (water supply and drainage, oil and gas, hydraulic steel pipes): The formation of pitted corrosion points leads to stress concentration, making them prone to cracking and leakage when under pressure. The reduction in wall thickness directly lowers the rated pressure-bearing capacity, and severely damaged pipes must be scrapped and cannot be used;
2. 2. Structural steel pipes (scaffolding, steel structure square and rectangular tubes): The effective cross-sectional area decreases, and the load-bearing capacity declines. There are safety hazards;
3. 3. Subsequent galvanization / painting: Incomplete cleaning of thick rust, flaking and peeling of the coating, accelerating further rusting.

1. Prevention of Scale Formation: Ensure that the pipes are protected from rain and moisture during storage. Control the temperature in the storage area to reduce condensation on the pipe walls. Cover the finished pipes with plastic film and rain shelters.
2. Prevention of Scale Growth: Remove the scale promptly within one month if it occurs. Apply anti-rust oil or primer and conduct regular inspections in damp environments.