Effective Corrosion Prevention for Stainless Steel Storage Tanks

To reduce the occurrence of accidents involving stainless steel storage tanks and protect them from corrosion caused by internal and external environmental factors, comprehensive anti-corrosion treatment is essential. This not only safeguards the tank's structure and extends its lifespan but also significantly lengthens the overhaul cycle of the tank, lowering maintenance costs. This article will discuss the causes of corrosion in stainless steel storage tanks, anti-corrosion measures, coating selection, and specific construction details.

Main Causes of Corrosion in Stainless Steel Tanks

Before exploring anti-corrosion measures, it's important to understand the primary causes of corrosion in stainless steel tanks. Corrosion not only affects the tank's normal operation but can also pose safety risks. Identifying the causes of corrosion is crucial for developing effective protection strategies.

1. Bottom Plate Corrosion and Perforation

Corrosion of the tank's bottom plate is one of the most common causes of accidents, particularly when the tank is in contact with groundwater or located in a humid environment. The alternating between full and empty tank states, along with seasonal temperature changes and groundwater levels, can make the bottom plate susceptible to corrosion. Groundwater can seep through cracks into the tank's bottom, causing electrochemical corrosion and accelerating damage.

2. Stray Current Effects

Stray current in the tank area is another significant cause of corrosion. This usually stems from incomplete cathodic protection systems in the network or interference from nearby welding machines, electrified railways, or DC equipment. When a tank is not adequately protected, stray currents can cause electrochemical corrosion, accelerating aging and deterioration.

3. Atmospheric Corrosion and Temperature Variations

The outer wall of stainless steel tanks is also subject to environmental corrosion. In coastal regions, acidic gases dissolved in rain or fog adhere to the tank's surface, causing a corrosive electrolyte film. Temperature fluctuations, particularly in extreme weather, accelerate this corrosion process, leading to electrochemical corrosion on the tank's exterior.

4. UV and Chemical Gas Damage

Long-term exposure to sunlight can cause the tank's outer coating to age, crack, and peel due to ultraviolet (UV) radiation. Meanwhile, corrosive gases in the atmosphere, such as hydrogen sulfide and chlorides, can further deteriorate the coating, reducing the tank's anti-corrosion capability.

Anti-Corrosion Measures for Stainless Steel Tanks

Effective anti-corrosion measures are essential to protect stainless steel tanks from corrosion, extend their service life, reduce the risk of accidents, and lower maintenance costs.

1. Coating Treatment

Applying a protective coating is an economical and effective way to shield the tank from corrosive media. Coatings isolate the metal surface from corrosive elements, delaying the aging process. However, coatings can develop cracks and peel over time, especially if applied poorly. Pinholes in the coating can accelerate localized corrosion, making high-quality application crucial.

2. Cathodic Protection

For tank bottom corrosion, cathodic protection is a highly effective method. It works by supplying concentrated electrical current to exposed metal, compensating for defects in the coating and preventing localized electrochemical corrosion. Cathodic protection is widely used to extend the service life of the tank bottom and reduce the need for frequent repairs.

3. Improving Construction Quality

Construction quality directly affects the effectiveness of anti-corrosion coatings. It is important to ensure that the coating is applied evenly and without pinholes, following standard thickness guidelines. Post-application inspections should be carried out to verify the integrity and performance of the coating.

Coating Selection and Anti-Corrosion Plans

Selecting the appropriate anti-corrosion coating is critical for ensuring the long-term stability of the tank based on its specific operating environment.

1. External Wall Coating Selection

For stainless steel tanks without insulation, the external environment plays a key role in coating selection. In coastal environments with high salt and humidity, a combination of zinc-rich epoxy primer, epoxy micaceous iron oxide intermediate paint, and polyurethane topcoat is often used. This system provides excellent corrosion resistance and UV protection, slowing down the aging process of the coating.

2. Bottom Coating Protection

The bottom of the tank, which is in contact with the ground or soil, requires similar anti-corrosion treatment as underground pipelines. Typically, two coats of epoxy asphalt, each 125 microns thick, are applied, for a total thickness of 250 microns. Alternatively, thick-film modified epoxy coatings, ranging from 200 to 300 microns, are also effective. These coatings provide good wear and corrosion resistance against groundwater and soil-based corrosive media.

3. Top Coating Protection

The coating system for the tank's top should be consistent with the external wall, taking into account atmospheric corrosion factors. Since the top of the tank often requires maintenance and inspection, it is important to include anti-slip design elements. A common approach is to scatter quartz sand of 60-80 mesh evenly on two layers of polyurethane topcoat to create a rough surface, reducing the risk of slips during maintenance work.

Anti-Corrosion Coatings for Chemical Storage Tanks

For chemical storage tanks, both the external environment and the corrosiveness of the internal chemical media must be considered when selecting anti-corrosion coatings. High-solids, solvent-free coatings with chemical resistance are often chosen for these tanks. These coatings not only provide environmental benefits but also enhance the tank's resistance to chemical corrosion, ensuring long-term stable operation.

Conclusion

Anti-corrosion treatment for stainless steel storage tanks is crucial, especially in harsh environments. By considering environmental factors and specific working conditions, appropriate anti-corrosion measures and coating systems can be selected. Utilizing high-quality coatings, cathodic protection, and strict construction processes will not only extend the service life of the tanks but also reduce accident risks, ensuring the safety and reliability of long-term operation.