The solution must wet all internal surfaces via circulation or spraying, leaving a protective, alkaline film on the steel after it dries. 3. Desiccant Dehumidification
Polythionic acid stress corrosion cracking is a catastrophic form of localized environmental cracking. It primarily attacks (such as unstabilized grades 304 and 316) and specific nickel-chromium-iron alloys. The Sensitization Mechanism
This is the most common method. The goal is to neutralize the acids that form on the metal surfaces. A mixture of soda ash ( Na2CO3cap N a sub 2 cap C cap O sub 3 ) and water is used, typically a soda ash solution (or lower, e.g., with a surfactant).
What is Polythionic Acid Stress Corrosion Cracking (PTA-SCC)? nace sp0170 pdf 2021
: Guidelines for selecting materials and fabrication practices that resist sensitization, reducing the inherent risk of PTA SCC. Dry Nitrogen Purging
Understanding NACE SP0170-2021: Protecting Refinery Equipment from Polythionic Acid SCC
: Keeping the equipment dry by circulating dry air (dew point below negative 15 raised to the composed with power C 5 raised to the composed with power F ) to stop the corrosion reaction. Exclusion of Air The solution must wet all internal surfaces via
Industry professionals following SP0170 typically employ one or more of the following primary protection methods: Nitrogen Purging
In the oil and gas industry, equipment failure is not just an operational downtime issue—it is a safety and environmental catastrophe waiting to happen. When we talk about transporting and processing "sour" hydrocarbons (containing hydrogen sulfide, or H₂S), the stakes are exponentially higher. Hydrogen sulfide doesn't just poison personnel; it destroys metal through a vicious mechanism known as .
) is often added to the wash to minimize the risk of chloride stress corrosion cracking, which can be triggered by standard wash water. It primarily attacks (such as unstabilized grades 304
Understanding NACE SP0170: Protecting Refineries During Shutdowns
Polythionic acid cracking is an insidious mechanism because it does not happen while the refinery is running. Instead, it occurs when three distinct variables intersect:
To ensure effective corrosion prevention in pipelines, operators should follow best practices outlined in NACE SP0170 PDF 2021: