What is the corrosion resistance of stainless steel towers
Information summary：The corrosion resistance of stainless steel towers mainly depends on the content and microstructure of alloy elements such as chromium and nickel in their materials. The following are the specific characteristics and advantages of their corrosion resistance:
1、 Corrosion resistance principle
The substrate of stainless steel towers is usually stainless steel (common grades such as 304, 316,
The corrosion resistance of stainless steel towers mainly depends on the content and microstructure of alloy elements such as chromium and nickel in their materials. The following are the specific characteristics and advantages of their corrosion resistance:
1、 Corrosion resistance principle
The substrate of stainless steel towers is usually stainless steel (common grades such as 304, 316, 316L, etc.), and its corrosion resistance is derived from the following characteristics:
1. Passivation film protection
When the chromium (Cr) content in stainless steel is ≥ 12%, it will react with oxygen in the air to form a dense and stable chromium oxide passivation film (Cr ? O3) on the surface. This film can prevent direct contact between internal metals and external corrosive media (such as water, acid, alkali, salt, etc.), thereby delaying corrosion.
For example, the passivation film of 304 stainless steel (Cr ≈ 18%, Ni ≈ 8%) can resist daily atmospheric, water, and steam corrosion; The passivation film of 316 stainless steel (with added Mo element) is more resistant to strong corrosive environments such as seawater and chemical media.
2. Synergistic effect of alloy elements
Nickel (Ni): enhances the toughness and acid corrosion resistance of stainless steel, and expands the stability range of passivation film.
Molybdenum (Mo): enhances resistance to reducing acids (such as sulfuric acid, hydrochloric acid) and pitting and crevice corrosion (such as 316L stainless steel).
Nitrogen (N): enhances strength and corrosion resistance, reduces the amount of nickel used (such as some economical stainless steels).
2、 Specific manifestations of corrosion resistance
1. Resistance to atmospheric corrosion
In a dry and clean atmosphere, stainless steel towers hardly rust.
In heavily polluted industrial or marine atmospheres (including sulfides and salt spray), high chromium nickel stainless steel (such as 316) can still maintain good corrosion resistance, while low-grade stainless steel (such as 201) may exhibit rust spots.
2. Corrosion resistance
It has excellent tolerance to neutral water media such as ordinary tap water and distilled water, and is not easily corroded after long-term immersion.
For water containing chloride ions (Cl ?) such as seawater and swimming pool water, high molybdenum stainless steel (such as 316L, 254SMO) should be selected, otherwise it may cause pitting corrosion or stress corrosion cracking.
3. Chemical corrosion resistance
Acid resistance: It has good corrosion resistance to oxidizing acids such as nitric acid and phosphoric acid (applicable to 304 stainless steel); For reducing acids such as hydrochloric acid and sulfuric acid, it is necessary to rely on molybdenum elements (such as 316L and 904L stainless steel).
Alkali resistance: Stainless steel has strong corrosion resistance to alkaline solutions such as sodium hydroxide (NaOH), and is widely used in alkali storage towers in the chemical and pharmaceutical industries.
Salt resistance: Avoid contact with salt solutions containing chloride ions (such as sodium chloride). High molybdenum stainless steel can be used in some salt environments.
4. Resistance to intergranular corrosion
Improper temperature during welding or heat treatment of stainless steel may lead to the precipitation of chromium carbide (Cr ? ∝ C ?) at grain boundaries, resulting in chromium depletion at grain boundaries and causing intergranular corrosion.
By selecting low-carbon grades (such as 304L, 316L) or adding stabilizing elements such as titanium (Ti) and niobium (Nb) (such as 321 stainless steel), intergranular corrosion can be effectively prevented.
3、 Factors affecting corrosion resistance
1. Material grade selection
Low corrosion environment: Optional 304 stainless steel (high cost-effectiveness).
Strong corrosive environment (such as marine, chemical): 316L, duplex stainless steel (such as 2205) or higher grade materials should be selected.
2. Surface condition
Rough surfaces are prone to accumulate dirt and grime, which may become the starting point of corrosion; Mirror polishing or passivation treatment can improve surface density.
3. Operating environment
High temperature, high humidity, and highly corrosive media (such as acid mist and seawater) can accelerate corrosion and require anti-corrosion coatings (such as epoxy resin) or regular maintenance.
4. Stress action
Stainless steel may undergo stress corrosion cracking (SCC) under the combined action of tensile stress and corrosive media, and it is necessary to reduce stress concentration through reasonable design.
4、 Application scenarios and advantages
Stainless steel towers are widely used due to their corrosion resistance
Chemical industry: acid/alkali storage tanks, reaction towers, waste gas treatment towers.
Food and medicine: Storage tanks and distillation towers in sterile environments (made of sanitary grade stainless steel, such as 316L).
Ocean engineering: seawater treatment tower for offshore platforms (requiring high chloride corrosion resistant materials).
Environmental protection equipment: aeration tower and desulfurization tower in sewage treatment (resistant to acid and alkali corrosion).
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