By removing the necessary reactants (air and water), the chemical pathway for polythionic acid formation is effectively blocked. 2. Neutralization (Alkaline Treatment)
The official document can be purchased and downloaded in PDF format from the AMPP Store (Association for Materials Protection and Performance).
Updated to a "Standard Practice" designation to align with modern metallurgical definitions.
When sulfide-containing equipment made of austenitic stainless steel is shut down and exposed to air (oxygen) and moisture (water), a chemical reaction occurs: oxygen and water react with sulfide corrosion products (iron sulfides) to form polythionic acid (H₂SₓO₆). This acid, combined with tensile stresses in the steel (often residual stresses from welding or fabrication), causes intergranular cracking. If not mitigated, this cracking can propagate rapidly, leading to leaks or catastrophic failures when the unit is repressurized.
To understand the weight of this standard, one must first understand the enemy. In refineries and petrochemical plants, equipment is often exposed to sulfide-containing environments. During normal operation, high temperatures keep these sulfides stable. However, during a shutdown—when equipment cools down and is exposed to air and moisture—these sulfides react to form Polythionic Acids (PTA). nace sp0170 pdf 2021
Primary objectives:
While search terms looking for the standard under a specific year (such as 2021) are common due to corporate procurement cycles, the document is officially tracked via its structural revisions. The core foundational versions include:
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.
Related search suggestions: functions.RelatedSearchTerms(suggestions:[suggestion:"NACE SP0170 2021 ECDA guidelines",score:0.9,suggestion:"External Corrosion Direct Assessment best practices",score:0.8,suggestion:"NACE SP0170 PDF download",score:0.7]) By removing the necessary reactants (air and water),
) precipitate along the grain boundaries. This depletes the adjacent areas of chromium—dropping it below the 12% threshold required for passive corrosion protection. This microstructural change is known as sensitization. The Three-Part Reaction Matrix
The most effective way to prevent PTA-SCC is to prevent the reaction between iron sulfide, oxygen, and water. Operators achieve this by filling and blanketing the equipment with high-purity .
While the standard was technically last updated in 2018, it is commonly referred to in modern updates, sometimes as NACE SP0170-2018 or via the AMPP store .
) typically keeps standards in effect for several years; the 2018 version remains the active guidance for preventing Polythionic Acid (PTA) Stress Corrosion Cracking (SCC) during refinery shutdowns. ANSI Webstore Core Content & Mitigation Methods Updated to a "Standard Practice" designation to align
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.
The standard highlights the need for properly selected materials, particularly stabilized grades of austenitic stainless steels (e.g., 321 or 347) which are more resistant to sensitization. Importance of the 2021/Updated Standard
AMPP - The Association for Materials Protection and Performance Overview of NACE SP0170
Under normal operations, sulfide scales form on the inside of pipes and vessels.