In numerous industrial applications, stainless steel offers satisfactory corrosion resistance. Based on experience, besides mechanical failure, corrosion of stainless steel water pipes mainly manifests in the following ways: A serious form of corrosion in stainless steel is localized corrosion (i.e., stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue, and crevice corrosion). These localized corrosion-related failures account for almost half of all failures. In fact, many failures can be avoided through proper material selection.
First, what are the causes of corrosion in stainless steel welded pipes?
1. Pitting corrosion: Pitting corrosion in stainless steel welded pipes is a form of localized corrosion that leads to corrosion.
2. Intergranular corrosion: Grain boundaries are disordered junctions between grains with different crystallographic orientations. Therefore, they are favorable areas for the segregation of various solute elements or the precipitation of metallic compounds (such as carbides and δ-phase) in the steel. Therefore, it is not surprising that grain boundaries may be corroded first in certain corrosive media. This type of corrosion is called intergranular corrosion, and most metals and alloys can exhibit intergranular corrosion in specific corrosive media.
3. Crevice Corrosion: Crevice corrosion in stainless steel welded pipes is a form of localized corrosion that can occur in stagnant crevices or within shielded surfaces. Such crevices can form at the junctions of metals with metals or metals with non-metals, for example, at contact with rivets, bolts, gaskets, valve seats, loose surface deposits, and marine organisms.
4. General Corrosion: This term describes corrosion that occurs relatively uniformly across the entire surface of a stainless steel welded pipe. When general corrosion occurs, the material gradually thins due to corrosion, eventually leading to material failure. Stainless steel can exhibit general corrosion in strong acids and alkalis. The failure caused by general corrosion is not particularly worrying because this type of corrosion can usually be resolved through a simple immersion test.
Second, what are the reasons for the corrosion of stainless steel welded pipes from the perspective of their corrosion mechanism?
1. Chemical Corrosion of Stainless Steel Welded Pipes
1.1 Surface Contamination: Oil, dust, acids, alkalis, and salts adhering to the surface of stainless steel welded pipes can transform into corrosive media under certain conditions. These media react chemically with certain components in the stainless steel, resulting in chemical corrosion and rust.
1.2 Surface Scratches: Various scratches damage the passivation film, reducing the protective ability of the stainless steel welded pipe and making it more susceptible to reaction with chemical media, leading to chemical corrosion and rust.
1.3 Cleaning: Incomplete cleaning after pickling and passivation can leave residual liquid that directly corrodes the stainless steel (chemical corrosion).
2. Electrochemical Corrosion of Stainless Steel Welded Pipes
2.2.1 Carbon Steel Contamination: Scratches caused by contact with carbon steel components can form galvanic cells with corrosive media, resulting in electrochemical corrosion.
2.2.2 Cutting: Cutting slag, spatter, and other easily rusting substances adhere to the surface and form galvanic cells with corrosive media, resulting in electrochemical corrosion.
2.2.3 Baking/Heating: The composition and metallographic structure of the flame-heated area change and become uneven, forming a galvanic cell with the corrosive medium and resulting in electrochemical corrosion.
2.2.4 Welding: Physical defects (undercut, porosity, cracks, lack of fusion, incomplete penetration, etc.) and chemical defects (coarse grains, chromium-depleted grain boundaries, segregation, etc.) in the welded area form a galvanic cell with the corrosive medium, resulting in electrochemical corrosion.
2.2.5 Material: Chemical defects (uneven composition, S, P impurities, etc.) and surface physical defects (porosity, sand holes, cracks, etc.) in stainless steel welded pipes facilitate the formation of a galvanic cell with the corrosive medium, leading to electrochemical corrosion.
2.2.6 Passivation: Poor pickling and passivation result in an uneven or thin passivation film on the stainless steel surface, making it prone to electrochemical corrosion.
2.2.7 Cleaning: Residual pickling and passivation solutions react with the stainless steel, and the resulting chemical corrosion products form electrochemical corrosion on the stainless steel parts.
Post time: Jan-21-2026