|4. Forms of Corrosion|
4.6 Stress Corrosion Cracking [4/4]
Material selection: Select suitable materials of construction resistant to SCC in the required environment. Substitute a more resistant alloy than the one that failed. For instance, substitute alloy 600 (chromium-nickel alloy) for alloy AISI 304 austenitic steel to avoid failure in a chloride environment if conditions allow.
Stresses: Keep stress levels as low as possible and stress relief where possible.
Species: Identify all the species in the service environment.
Change environment: For instance eliminate oxygen or oxidizing agents to reduce cracking of service conditions permit.
Coatings: Barrier coatings can be used to control cracking as they isolate the material from the environment.
Cathodic protection: In case of chloride induced SCC, cathodic protection may be applied to polarize the structure to a potential moer reducing then the SCC range. Cathodic protection may lead to problems of hydrogen embrittlement, when hydrogen is generated on the surface.
Inhibitors: Use inhibitors to minimize SCC after proper assessment of the dosage and its previous history. Phosphates and other organic and inorganic inhibitors have been successfully used to reduce SCC in mildly corrosive media.
Induce residual compressive stress: The compressive stress offsets the applied tensile stress. It can be achieved mechanically by slot penning.
Welding procedures: It involves the use of low hydrogen electrode, pre-heating and post-heating the weldment.
Design: Designs involving smooth corners, which do not alloy stagnation of the liquid are helpful in minimizing corrosion.