Prolonged use in strong acid environments leads to gradual changes in the thickness of stainless steel plates. This process is closely related to the material properties of stainless steel, the type and concentration of the acid, and the temperature. The corrosion resistance of stainless steel primarily stems from the dense chromium oxide passivation film formed on its surface. This film effectively blocks oxygen and moisture from contacting the internal metal, thus slowing down the corrosion process. However, in strong acid environments, the passivation film can be damaged, accelerating corrosion and causing thickness changes.
Under the action of strong acids, the passivation film on the surface of the stainless steel plate gradually dissolves, especially when the acid is highly oxidizing or concentrated, significantly accelerating the dissolution rate. For example, nitric acid, a strong oxidizing acid, can both promote the formation of the passivation film on the stainless steel surface and dissolve and disrupt its formation process. As the passivation film is damaged, uniform corrosion begins on the stainless steel surface, and the material gradually thins. If corrosion intensifies further, grain breakage and detachment may occur on the stainless steel surface, leading to varying degrees of corrosion thinning, significantly weakened surface grain strength, and a marked reduction in the bonding force between the surface grains and adjacent internal grains.
Different types of strong acids exhibit varying corrosion mechanisms on stainless steel plates. Sulfuric acid, as a non-oxidizing acid, is highly corrosive to stainless steel under high temperature or high concentration conditions. The corrosion rate of 304 stainless steel already increases significantly at around 80℃ in 3% sulfuric acid; further increases in temperature or sulfuric acid concentration will intensify corrosion. Strong acids containing chloride ions, such as hydrochloric acid, easily induce pitting and stress corrosion cracking in stainless steel. Chloride ions damage the passivation film, causing localized corrosion pits on the stainless steel surface, leading to uneven thickness and reduced structural strength.
Temperature is one of the key factors affecting the thickness change of stainless steel plates in strong acid environments. As temperature increases, the oxidizing and reactivity of the acid increases, significantly accelerating the corrosion rate. For example, in a nitric acid environment, increased temperature promotes stainless steel corrosion, and the higher the nitric acid concentration, the more pronounced the temperature-driven corrosion effect. In high-temperature nitric acid vapor, stainless steel is more prone to intergranular corrosion, and the corrosion is more severe than in aqueous solutions. Intergranular corrosion propagates along grain boundaries, causing grain detachment and further exacerbating thickness reduction.
The material composition of stainless steel plates significantly impacts their thickness variation in strong acid environments. High-chromium, high-nickel stainless steels (such as type 316), containing molybdenum, exhibit significantly better resistance to pitting corrosion and acids/alkalis than type 304 stainless steel. Molybdenum stabilizes the passivation film, inhibiting the penetration of corrosive ions such as chloride ions, thus slowing down the corrosion process. Therefore, for long-term use in strong acid environments, selecting high-performance molybdenum-containing stainless steel can effectively reduce the rate of thickness change and extend service life.
Furthermore, the thickness variation of stainless steel plates in strong acid environments is also affected by surface condition, stress distribution, and medium flowability. Stainless steel plates with high surface roughness or defects such as scratches and welds are more prone to localized corrosion in strong acids, leading to uneven thickness. Residual or applied stress exacerbates the risk of stress corrosion cracking, especially in strong acid environments containing chloride ions, where crack propagation accelerates and thickness variations become more pronounced. Poor medium flowability or the presence of stagnant zones allows corrosion products to accumulate, forming concentration cells, accelerating localized corrosion, and causing rapid thickness reduction.
To mitigate thickness changes in stainless steel plates in strong acid environments, various protective measures can be implemented. These include: improving the corrosion resistance of stainless steel through alloying; selecting high-performance stainless steels containing elements such as molybdenum and nitrogen; optimizing structural design to reduce gaps and stress concentration areas; controlling the temperature and concentration of the medium to avoid extreme conditions; using coatings or linings to protect the stainless steel from direct contact with strong acids; and conducting regular inspections and maintenance to promptly detect and address corrosion problems.
