The standard aims to provide a comprehensive framework for preventing and controlling corrosion in equipment and components, ensuring safe and reliable operation, and minimizing the risk of corrosion-related failures.
During normal refinery operations, sulfur compounds react with iron to form metal sulfide scales inside process equipment. When the unit is shut down for maintenance, two atmospheric elements enter the system: and moisture ( H2Ocap H sub 2 cap O ) .
When the equipment is opened, air (oxygen) and moisture enter. nace sp0170 pdf 2021
The solution must be allowed to soak, and in some cases, a subsequent wash with deionized water is recommended to prevent chloride stress cracking. B. Dry Air Purge (Dehumidification)
During normal refinery operations, hydroprocessing units (like hydrocrackers, hydrotreaters, and desulfurizers) process sulfur-heavy hydrocarbon streams at elevated temperatures. Sulfur species react with the iron, nickel, and chromium in steel to form stable metal sulfide scales along the internal surfaces of the piping and vessels. The standard aims to provide a comprehensive framework
The primary objective of SP0170 is to provide reliable mitigation methods to prevent Polythionic Acid Stress Corrosion Cracking (PTA SCC). This form of cracking occurs when sensitized austenitic stainless steels react with oxygen and water in the presence of sulfide corrosion products—common in refinery units like hydrocrackers and hydrotreaters—during shutdown periods. Core Mitigation Practices
The following represents a summary of the key consequences for non-compliance with NACE SP0170: When the equipment is opened, air (oxygen) and
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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
The equipment is washed with an alkaline solution, usually a mixture of water and soda ash (Na₂CO₃), or sometimes ammonia.