If the vessel must be opened to the air for maintenance or internal inspection, the internal surfaces must be treated with an alkaline solution before oxygen can react with the sulfides.
By removing the necessary reactants (air and water), the chemical pathway for polythionic acid formation is effectively blocked. 2. Neutralization (Alkaline Treatment)
: When implementing measures to control stray-current corrosion, adhering to the guidelines in NACE SP0170 can help ensure compliance with industry best practices. This is particularly important for maintaining asset integrity, safety, and environmental protection.
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When equipment must be opened to atmospheric air for repairs, cleaning, or internal inspection, the metal sulfide surfaces must be treated to prevent acid formation.
Official digital PDF downloads and printed versions of this standard can be secured directly through authorized nodes like the Accuris Standards Store NACE SP0170-2018 Page or the ANSI Webstore .
To avoid unpredicted downtime and major equipment failures, the standard details three primary mitigation methodologies used depending on whether the equipment will be opened, inspected, or left sealed. Mitigation Method Primary Mechanism Ideal Application nace sp0170 pdf 2021
During operations, hydrogen sulfide ( H2Scap H sub 2 cap S
) 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
Hardness is the single most important indicator of SSC resistance. The 2021 PDF introduces more stringent maximum hardness values for heat-affected zones (HAZ) in welds, especially for components exposed to H₂S partial pressures above 10 psi. If the vessel must be opened to the
Engineers looking up historical or current iterations should note the systemic changes in how corrosion standards are cataloged. Historically published by NACE International, these guidelines underwent a major organizational shift when NACE merged with the to form AMPP .
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