Why Does Surface Corrosion Occur on Stainless Steel Welded Pipes?

Corrosion damage to stainless steel pipes can generally be categorized into two types: general corrosion and localized corrosion. Corrosion typically refers to uniform or non-uniform distribution across the entire surface of a component. Today, stainless steel pipe manufacturers will explain: Why does surface corrosion occur on stainless steel welded pipes?

 

 

1. Dust

During stainless steel welded pipe processing, dust particles in the surrounding environment often settle on the pipe surface. Such dust can be removed with water or alkaline solutions. However, if the contamination is sticky, high-pressure water jets should be used for cleaning. Failure to clean promptly may lead to surface corrosion of the stainless steel welded pipe.

 

2. Loose Iron Particles or Embedded Contaminants

Free iron on the surface of stainless steel welded pipes can cause rust and corrosion. Therefore, it must be removed. Loose iron particles can usually be cleared along with dust. Those with stronger adhesion must be treated as embedded iron.

Beyond dust, surface iron contamination stems from multiple sources. These include cleaning with ordinary carbon steel wire brushes, shot blasting using sand, glass beads, or other abrasives previously employed on carbon steel, low-alloy steel, or cast iron components, or grinding non-stainless steel items near stainless steel parts or equipment. If stainless steel pipe manufacturers fail to implement protective measures during cutting or handling operations, iron particles from steel cables, lifting equipment, or work surfaces can easily embed into or contaminate the surface.

 

3. Scratches

To prevent the accumulation of process lubricants, product residues, or contaminants, rough surfaces such as scratches on stainless steel welded pipes must undergo mechanical cleaning to achieve a smooth finish.

 

4. Heat-affected zones and other oxide layers

During welding or grinding, stainless steel pipes heated to high temperatures in air develop chromium oxide heat-tempered colors on both sides of the weld, the underside, and the base. These colors are thinner than the oxide protective film and clearly visible. Their appearance varies with thickness, ranging from iridescent, blue, or purple to pale yellow and brown. Thicker oxides are typically black.

 

5. Rust Spots

Occasional rusting on stainless steel pipes or equipment indicates severe surface contamination. Rust must be removed before equipment commissioning. Thoroughly cleaned surfaces should be verified via iron tests and/or water tests.

 

The above outlines factors causing corrosion in stainless steel welded pipes and corresponding preventive measures. We hope this information from stainless steel pipe manufacturers proves helpful.

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