Can 18-8 stainless steel be used in materials containing chloride ions?

Austenitic stainless steel should preferably not be used in environments containing Cl- ions

The 18-8 series of stainless steels belongs to the austenitic stainless steels; chloride ions are particularly sensitive to them, causing easy corrosion

The 18-8 series stainless steels belong to the austenitic stainless steels, and chloride ions can easily corrode them. The principle behind this is that metals in a passive state still possess a certain degree of reactivity, meaning that the dissolution and restoration (re-passivation) of the passivation film are in dynamic equilibrium. When the medium contains active anions (such as chloride ions), the equilibrium is disrupted and dissolution becomes dominant. The reason is that chloride ions can preferentially and selectively adsorb onto the passivation film, displacing oxygen atoms, and then combine with the cations in the passivation film to form soluble chlorides. As a result, small pits (with pore sizes of 20–30 μm) are formed at specific points on the newly exposed base metal. These small pits are known as pitting nuclei, and can also be regarded as the active centers where pitting occurs. The presence of chloride ions has a direct destructive effect on the passive state of metals

Stainless steel owes its properties to a passivation film formed on its surface; chloride ions, being small in size, can penetrate everywhere and break through this water film (through electrochemical corrosion), thereby destroying the passivation film on the metal surface and generating trivalent iron ions that increase the metal’s conductivity.

Although chloride ions are the main factor causing corrosion and damage to stainless steel, this applies under acidic and neutral conditions. The user is working with alkaline substances at room temperature, and the properties of these substances are not well known. It is therefore recommended to conduct tests to make a decision, such as carrying out suspension testing for a certain period of time or using electrochemical methods to determine the pitting potential.

I’m currently facing a problem similar to that of the original poster. The solution contains mainly CaCl2, at around 150 mg/l. Is it possible to use 304 stainless steel for pipes and equipment in such conditions? What is the corrosion rate of 304 in such an environment? Is there a standard regarding the operating environment for stainless steel? For example, at what maximum level can devices made of 304 be used? I would appreciate it if experts could help answer this! ! !

304 steel cannot be used in the upper floors, as the concentration of chloride ions is already very high. Moreover, the hydrolysis of CaCl causes the solution to become acidic. The corrosion caused by chloride ions on SS is mainly pitting corrosion; therefore, the corrosion rate cannot be used as a criterion for evaluation.

It’s best not to use it; there are many other materials that can serve as substitutes for 18-8.

Weld corrosion progresses fastest, usually manifesting in the form of perforations