1.What is the difference in corrosion resistance between galvanized steel and stainless steel in coastal areas and marine engineering applications?
Galvanized steel: High humidity + salt (such as NaCl) will accelerate the electrochemical corrosion of the zinc layer. Zinc reacts with chloride ions to form zinc chloride, which is easily soluble in water, causing the coating to gradually wear out. For example, if the galvanized steel components of coastal bridges are not regularly maintained, large areas of coating may peel off within 5-10 years.
Stainless steel (such as 304/316): The passivation film is highly stable in a neutral salt spray environment. 316 stainless steel contains molybdenum, and its resistance to chloride ion corrosion is significantly better than that of galvanized steel. It is often used in offshore platforms, ship accessories, etc., and its service life can reach more than 20 years.
2.What is the difference between galvanized steel and stainless steel in corrosion resistance in high humidity industrial environment applications?
Galvanized steel: Water vapor and oxygen in humid air will form an electrochemical corrosion environment, and the zinc layer will gradually oxidize into white zinc oxide powder (white rust). If it is not cleaned in time, it will accelerate the rust of the substrate.
Stainless steel: The passivation film is not easily destroyed in a humid environment, especially under non-acidic condensation conditions, and the corrosion resistance advantage is obvious (such as stainless steel equipment in bathrooms and food processing workshops).
3.What is the difference in corrosion resistance between galvanized steel and stainless steel in acidic environments?
Galvanized steel: Strong acids such as dilute sulfuric acid and hydrochloric acid react directly with zinc to generate hydrogen and soluble zinc salts, causing the coating to dissolve quickly. For example, galvanized pipes exposed to acidic industrial wastewater may be perforated within a few months. ◦ In a weakly acidic environment (such as acid rain, pH < 5.6), the corrosion rate of the zinc layer is about 5-10 times that of stainless steel.
Stainless steel: 304 stainless steel has good corrosion resistance in medium-concentration non-oxidizing acids (such as dilute sulfuric acid), but pitting may occur if the acid concentration is high or contains chloride ions (such as hydrochloric acid); 316 stainless steel is more resistant to chloride ion pitting and is suitable for chemical pickling equipment.
4.What is the difference in corrosion resistance between galvanized steel and stainless steel in an alkaline environment?
Galvanized steel: Strong alkali (such as NaOH) will react with zinc to form soluble zincate, causing corrosion of the coating. For example, if galvanized steel is used in alkaline solution pipelines in paper mills, the coating may fail due to alkali corrosion.
Stainless steel: The passivation film is highly stable in alkaline environments and is suitable for use in alkaline media such as laundries and printing and dyeing plants.
5.What is the difference between the corrosion resistance of galvanized steel and stainless steel in chloride environments?
Galvanized steel: Chloride ions (such as NaCl in seawater and road deicing agents) will destroy the oxide film on the surface of the zinc layer, forming local corrosion cells and accelerating the loss of zinc. For example, in winter in the north, the corrosion rate of galvanized steel guardrails on roads and bridges where salt is spread is 3-5 times higher than in ordinary environments.
Stainless steel: 304 stainless steel may experience pitting or stress corrosion cracking in high concentrations of chloride (such as seawater); 316 stainless steel contains molybdenum, which significantly improves its resistance to chloride ion corrosion and is often used in seawater desalination equipment.