Ensure surfaces remain coated with the soda ash residue during air exposure. Continuous chemical protection.
The technical standard , officially titled "Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress Corrosion Cracking During a Shutdown of Refinery Equipment," is a foundational document for asset integrity in the petroleum refining industry. Maintained by the Association for Materials Protection and Performance (AMPP) , this standard maps out exact operational workflows to shield critical components from devastating, rapid structural failures during planned downtimes.
Understanding NACE SP0170: Protection of Austenitic Stainless Steels from Polythionic Acid SCC
The standard explains the electrochemical process behind Polythionic Acid Stress Corrosion Cracking (PASCC). It details the specific alloy types that are susceptible (such as 304SS, 316SS, and Incoloy alloys) and identifies the "danger zone" of temperatures and environments where cracking is most likely to occur during a shutdown. nace sp0170 pdf
When a piece of equipment does not need to be opened for internal maintenance, the most effective defense is to completely isolate it from air.
The Four-Hour Fire and a Paragraph on Page 23
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Equipment is purged and kept under a continuous positive pressure blanket of dry, high-purity nitrogen ( N2cap N sub 2
Austenitic stainless steels are highly valued in the refining and petrochemical industries for their excellent corrosion resistance and high-temperature strength. However, these materials are susceptible to a severe form of localized corrosion known as Polythionic Acid Stress Corrosion Cracking (PTA-SCC).
This document serves as a comprehensive guide to NACE SP0170, a critical standard for maintaining the integrity of refinery equipment. It is designed for corrosion engineers, integrity managers, and plant operators seeking to understand, implement, or source the official NACE SP0170 PDF. This article details the standard's scope, technical basis, practical applications, and provides essential guidance on obtaining the official document. Maintained by the Association for Materials Protection and
Here is what you will find inside the document:
Shutdown, inspection, and startup scenarios in refineries.
The (Standard Practice) provides crucial guidelines for protecting austenitic stainless steels and other austenitic alloys from Polythionic Acid Stress Corrosion Cracking (PTA SCC) . This type of corrosion typically occurs during the shutdown of refinery equipment when sulfide corrosion products react with air and moisture. Key Mitigation Strategies
The standard outlines several acceptable protection methodologies depending on whether the equipment needs to be opened for internal inspection/maintenance or kept closed during the turnaround. 1. Exclusion of Oxygen (Nitrogen Purging)