What are the causes of surface corrosion on thin-walled stainless steel pipes

As people's requirements for the hygiene and safety of drinking water have increased, stainless steel water pipes have been widely used in public buildings and urban residences. The occurrence of corrosion damage in stainless steel pipes can generally be divided into two types: general corrosion and local corrosion. Corrosion usually refers to the corrosion that occurs uniformly or non-uniformly over the entire surface of the component. This kind of corrosion is easily noticed and easier to deal with. Now let's take a look at the causes of corrosion on the surface of stainless steel pipes. 

Corrosion usually does not affect the entire surface of stainless steel pipes, but occurs only within or around the defects. This kind of localized corrosion problem is generally referred to as pitting corrosion or crevice corrosion, and both will cause corrosion to penetrate deep and spread widely, but will not affect the majority of the surface of the pipes. Let's first talk about the causes of surface corrosion on thin-walled stainless steel pipes. 

1. Dust

In production processing enterprises, there are often areas with dust. The dust in the ambient air will continuously settle on the surface of the stainless steel thin-walled tubes. These dust particles can be washed off with water or alkaline solutions. However, if the dirt is sticky, a high-pressure water gun should be used for cleaning. 

2. Floating iron powder or embedded iron

On the surface of thin-walled stainless steel pipes, free iron can cause rust and corrosion of the pipes. Therefore, it must be removed. Floating iron powder can usually be removed along with the dust. For some with stronger adhesion, it must be treated as embedded iron. 

Apart from dust, there are many sources of surface iron. These include cleaning with ordinary carbon steel wire brushes and shot peening treatment using sand, glass beads or other abrasives previously used on plain carbon steel, low alloy steel or cast iron parts, or grinding of non-stainless products near stainless steel components and equipment. If no protection measures are taken for stainless steel during cutting or lifting processes, iron from steel wire ropes, lifting equipment and workbenches can easily embed in or contaminate the surface. 

3. Scratches

To prevent the accumulation of process lubricants, products or dirt, it is necessary to mechanically clean the rough surfaces such as scratches on the thin-walled stainless steel tubes to make them smooth. 

4. Heat Tempering Color and Other Oxidation Layers

During the welding or polishing process, there is no such thing as food-grade stainless steel tubes available. When stainless steel tubes are exposed to high temperatures in the air, the weld seams, the underside of the weld seams, and the bottom surfaces will all develop a chromium oxide heat tempering color. This heat tempering color is thinner than the oxidation protection film and is clearly visible. The color is determined by its thickness and can present as a rainbow color, blue, purple to light yellow and brown. Thicker oxides are usually black. 

This is due to their prolonged exposure to high temperatures. Whenever any of these oxide layers form, the chromium content on the metal surface decreases, resulting in a reduction in the corrosion resistance of these areas. Not only must the heat tempering color and other oxide layers be removed, but the precision tubes must also clean the chromium-poor metal layer beneath them. 

5. Rust Stains

Sometimes, rust spots may appear on thin-walled stainless steel pipes or equipment, indicating that the surface of the pipe material has been severely contaminated. Before the equipment is put into use, the rust must be removed. The surface that has been thoroughly cleaned should be tested through a rust test and/or a water test. 

The above are the factors causing corrosion of thin-walled stainless steel pipes and the corresponding prevention measures. The reasons for the electrochemical reaction of the pipe materials include poor corrosion resistance of the material, acidic substances, and surface scratches. Therefore, to prevent corrosion, it is necessary to select materials with stronger corrosion resistance; apply a transparent silicone resin protective film on the surface; and avoid intense collisions or friction between the thin-walled stainless steel pipes and other objects.