Nitric pitting is a common form of localized corrosion that occurs in materials such as stainless steel, titanium, and other alloys. It is a result of chemical reactions that occur on the surface of the metal when exposed to an oxidizing environment, particularly in the presence of nitric acid. This article will explore the process of nitric pitting, its causes, and how to prevent it.

The Process of Nitric Pitting

Nitric pitting is a form of corrosion that is characterized by small, localized holes or pits on the surface of the metal. The process of nitric pitting involves the following steps: Formation of a passive oxide layer: When a metal is exposed to an oxidizing environment, it forms a passive oxide layer on the surface. This layer protects the metal from further corrosion. Breakdown of the passive oxide layer: If the passive oxide layer is damaged or disrupted, the metal is exposed to the environment, and corrosion can occur.
Formation of pits: Once the passive oxide layer is broken down, the metal is exposed to the environment, and pits can form on the surface. These pits can be small and localized or grow and merge to form larger areas of corrosion.

How is Nitric Pitting harder to clean?

When pitting occurs, it can make it significantly harder to clean a metal surface. This is because the pits create small cavities on the surface of the metal, which can trap dirt, debris, and organic material. These contaminants can then react with the metal surface and exacerbate the corrosion, leading to further damage.

Cleaning a metal surface that has pitting can be challenging, as the cavities created by the pits can be difficult to access and clean thoroughly. Traditional cleaning methods such as wiping, scrubbing, or blasting may not be effective in removing the contaminants from the pits. In addition, aggressive cleaning methods can further damage the metal surface, leading to more pitting.

How we can remedy the issue caused by Nitric Acid?

Our chemicals are crafted to have low surface tension and can provide a balanced chelator solution. If the damage has already been done and pitting is present our solutions can still clean thoroughly and completely.

What is an acceptable corrosion rate with Nitric Acid?

ZERO.
√ 2-3 mils per year – Generally using nitric acid systems. √ Above 5 mils per year – Unacceptable corrosion control.
2-3 mils/year the corrosion will fill up with organic material and cause cleaning nearly
impossible, however with our prebatch 20+ complete, the residual will attack the micro pits because we have a 19/ dyne/ cm surfactant balanced with the appropriate chelators, along with the correct concentration of liquid caustic soda.

Conclusion?

Nitric pitting is a common form of localized corrosion that can occur in metals such as stainless steel and titanium. It is caused by the breakdown of the passive oxide layer on the surface of the metal, leading to the formation of pits. Nitric acid has been used primarily because of its low cost. In the past, other products such as phosphoric acid had been used however, the cost is significantly higher but prevents the pitting.

Interested in setting up a CIP Trial?