Polythionic Acid Stress Corrosion Cracking
The chemical reaction of sulfur compounds, oxygen, and water at elevated temperatures, which typically occurs during process unit shutdowns, can lead to the formation of oxoacids known as polythionic acids (PTAs). These acids can destroy the passive oxide layer of austenitic steels and alloys. Consequently, if the austenite stainless steel is sensitized and subjected to stress, it can lead to an intergranular cracking phenomenon known as Polythionic Acid Stress Corrosion Cracking (PTASCC). This mechanism can occur in any unit that using sensitized austenitic material in high-temperature sulfur containing environments. PTASCC is typically seen in FCC regenerators and heater/furnace tubes in crude and hydroprocessing units.