【Basic Knowledge 21】Pitting and Its Prevention (Prize Quiz)

Most of the metal surface does not corrode or only experiences slight corrosion, while in certain areas small corrosion pits form and spread deeper into the material; this phenomenon is known as pitting or spot corrosion. Pitting is a destructive and highly problematic form of corrosion. Factors affecting pitting corrosion: (1) Properties of the metal. The higher the pitting potential of the metal, the better. Then pitting corrosion is less likely to occur. Metals or alloys with self-passivation properties are more susceptible to pitting corrosion. The weaker the passivation ability, the higher the sensitivity. (2) Surface condition of the metal: Generally speaking, pitting is less likely to occur on smooth and clean surfaces, whereas surfaces covered with dust or various metallic and non-metallic impurities are prone to pitting. A rough surface resulting from cold working, or welding slag remaining on the surface, can easily lead to pitting in such areas. (3) Environmental factors: Most pitting corrosion occurs in media containing chloride ions or chlorides. Experiments show that under anodic polarization, the presence of chloride ions in the medium is sufficient to cause pitting in the metal. Therefore, chloride ions can also be referred to as the “trigger” for pitting. Furthermore, as the chloride ion concentration in the medium increases, the pitting potential decreases, making pitting more likely to occur. In an alkaline medium, as the pH value increases, the Ebr value of the metal becomes significantly more positive, thereby slowing down the occurrence of pitting. There are different views regarding the effect of pH value in acidic media; some researchers have found that as the pH value increases, the Ebr value rises slightly, while others believe that pH value actually has no impact on the Ebr value. As the medium temperature increases, the Ebr value of metals decreases significantly, accelerating pitting. Medium flow will slow down the occurrence of pitting. The flow rate of the medium increases. On one hand, this facilitates the delivery of dissolved oxygen to the metal surface, making it easier for a passivation film to form ； On the other hand, it can reduce the chances of sediment deposition on the metal surface, thereby decreasing the likelihood of pitting.

Pitting corrosion, also known as spot corrosion, refers to a type of corrosion in which the degradation is concentrated in a very small area on the metal surface and penetrates deep into the metal in the form of pits.

Pitting, also known as spot corrosion, refers to a type of corrosion in which the degradation is concentrated in a very small area on the metal surface and penetrates deep into the metal in the form of pores. It can improve surface smoothness and provide paint corrosion protection.

Metal corrodes deeply at a single point

What is pitting corrosion? What are the ways to prevent it? What is pitting corrosion? Answer: Most of the metal’s surface does not corrode, or corrosion is very slight. When small corrosion pits appear in certain areas and progress deeper, this phenomenon is known as pitting corrosion, or simply pitting. What are the ways to prevent it? Answer: Choose high-quality materials. Add a corrosion inhibitor.

Definition: The local passivation film on the surface of stainless steel is damaged, resulting in pinpoint corrosion pits that grow vertically to form \"deep pits\", and may even cause perforations in the container walls. Prevention and control: Ensure that the passivation film is smooth and free of defects, prevent chloride ions from damaging the passivation film, and avoid local concentration of the medium or accumulation of deposits.

A type of localized corrosion that occurs locally on the metal surface and spreads rapidly inward into the metal. Prevention methods: 1. Choose high-quality materials ； 2. Natural corrosion inhibitor.

Pitting corrosion refers to a type of corrosion in which the degradation is concentrated in a very small area on the metal surface and penetrates deep into the metal as pores. Preventive measures: Reduce inclusions in steel, especially sulfur content ； Secondly, it is to improve the pitting resistance of the steel matrix; the alloying elements that affect the corrosion resistance of the matrix are mainly chromium, molybdenum, and nitrogen

Pitting corrosion, also known as spot corrosion, refers to a type of corrosion in which the degradation is concentrated in a very small area on the metal surface and penetrates deep into the metal in the form of pores. Corrosion inhibitors and electrochemical protection methods can be used to prevent pitting corrosion