: Using dry nitrogen to exclude oxygen and moisture from the equipment, preventing the formation of polythionic acid. Alkaline Washing
The standard provides specific mitigation methods to protect equipment—such as heaters, tubes, and reactors—during the downtime, shutdown, and startup phases of refinery operations. PTA SCC occurs when sulfide corrosion products react with oxygen and water to form polythionic acids, which can rapidly cause cracking in sensitized austenitic alloys.
This creates an immediate asphyxiation hazard; therefore, rigid tagging and isolation protocols must be followed. 3. Temperature Control (Dew Point Prevention) nace sp0170 pdf 2021
for preventing polythionic acid stress corrosion cracking (PTA SCC) in refinery equipment. While users often search for a "2021 PDF" version due to standard review cycles or the AMPP (Association for Materials Protection and Performance) merger era, the 2018 edition is the current, reaffirmed version used globally by corrosion engineers.
: Neutralizes any PTA that may form. The standard emphasizes that solutions must be properly applied to all surfaces and warns of potential effects on catalysts. : Using dry nitrogen to exclude oxygen and
: Used to exclude oxygen and moisture from the equipment during shutdown. Alkaline Washing (Soda Ash Wash)
is a Standard Practice published by NACE International (now merged into AMPP ) titled "Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress Corrosion Cracking During a Shutdown of Refinery Equipment" . While users often search for a "2021 PDF"
: When austenitic stainless steels are exposed to high operational temperatures—typically between 425°C and 815°C (800°F to 1500°F) —chromium carbides precipitate along the grain boundaries. This depletes the adjacent zones of chromium, leaving the grain boundaries highly vulnerable to localized corrosion.
