Chloride Stress Corrosion Cracking Of 300 Series Stainless Steel

By Dr. Hira Ahluwalia, Material Selection Resources Inc. (MSR)

Stress corrosion cracking (SCC) is the unexpected, sudden failure of normally sound materials when subjected to tensile stress in a corrosive environment. The conditions necessary for stress corrosion cracking are:

• Suitable Environment: The most common corrosive species that has caused failures in chemical plant is the chloride ion. Chloride stress corrosion cracking (CSCC) can occur in hot acid chloride solutions, sodium chloride/peroxide solutions, and seawater. Other neutral halides such as bromides, iodides, and fluorides can also cause SCC of the 300 series stainless steels.
• Tensile Stress: The combination of residual stresses from welding, the cold work from fabrication, and the cyclic stress from operating conditions are sources of tensile stress that, when above a certain threshold stress, will make the metal susceptible to stress corrosion cracking.
• Sensitive Material: The alloy content of stainless steels, particularly nickel, determines the sensitivity of the metal to SCC. The most common grades of stainless steel, 304L, 316L, 321, 347, have nickel in the range 8-10% and are the most susceptible to SCC. Ferritic stainless steels that are nickel free, and the high nickel alloys are not subject to SCC.