What specific (e.g., 304, 316, 347) are in your unit?
NACE SP0170-2021 is an indispensable tool for protecting sensitized austenitic stainless steel equipment from the disastrous effects of PTA SCC. By following the procedures for alkaline washing and excluding oxygen during shutdowns, refiners can significantly extend the life of their equipment and prevent catastrophic failures during startup.
) during welding or high-temperature process operations, chromium carbides precipitate along the grain boundaries. This depletes the adjacent zones of chromium, rendering them vulnerable to localized corrosion.
PTA SCC is a severe corrosion mechanism that particularly threatens equipment made from the common 300-series stainless steels (e.g., Types 304, 316, 321, 347) and their alloys. The cracking occurs when these materials are exposed to , which form from the reaction of: nace sp0170 pdf 2021
Understanding PTA SCC (Polythionic Acid Stress Corrosion Cracking)
: The relative humidity inside the vessel must be kept below 20% to 30% , ensuring that the internal metal surface temperature always remains safely above the ambient dew point to prevent condensation. Material Selection Considerations
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This is a must-read for Materials Engineers, Corrosion Specialists, and Process Engineers looking to mitigate pitting and system failures.
: Before the equipment drops below the dew point, the process environment is completely purged with high-purity dry nitrogen gas.
) reacts with the steel elements to form ( The cracking occurs when these materials are exposed
NACE SP0170 is specifically designed to prevent . PTA SCC is a particularly dangerous failure mode because it can lead to catastrophic brittle fractures of equipment made of austenitic stainless steel, specifically during plant shutdowns or start-ups.
When equipment must be opened to atmospheric air for repairs, cleaning, or internal inspection, the metal sulfide surfaces must be treated to prevent acid formation.
: The official source for the SP0170 standard.
: Guidelines for selecting materials and fabrication practices that resist sensitization, reducing the inherent risk of PTA SCC. Dry Nitrogen Purging
Equipment that must be opened to the atmosphere for internal inspection or catalyst dumping.