) is pumped into the system to maintain a slight positive pressure.
The standard outlines several strategies to prevent the formation of polythionic acid or to neutralize it before damage occurs: NACE SP0170-2018
Polythionic acid stress corrosion cracking is a form of rapid, intergranular cracking that occurs predominantly in (such as 300-series stainless steels like 304 and 316) and high-nickel austenitic alloys. The Chemical Mechanism
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 . nace sp0170 pdf 2021
: While the core document was comprehensively revised in late 2018 ( NACE SP0170-2018 ), it remains a primary technical requirement referenced in standard industry compliance portfolios. The Mechanics of Polythionic Acid SCC (PTA SCC)
When utilizing an alkaline wash, use chloride-free or low-chloride water. High-chloride water can inadvertently trigger Chloride Stress Corrosion Cracking (Cl-SCC).
Stay safe, stay compliant, and always refer to the most current standard. ) is pumped into the system to maintain
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PTA requires moisture to form. Removing moisture removes the hazard.
: The standard covers topics such as the effects of stray current, methods for detecting and measuring stray currents, and mitigation techniques. Its primary purpose is to offer guidance on protecting buried or submerged metallic structures from corrosion caused by stray electric currents. When we talk about transporting and processing "sour"
This acid seeks out "sensitized" areas in the steel (often near welds) and causes rapid, microscopic cracking. Equipment that looked perfect yesterday can literally fall apart tomorrow. Mitigation: The SP0170 Playbook
) partial pressures. This creates thick, iron-sulfide corrosion scales that become high-risk zones for PTA generation upon shutdown.
: These acids are relentless. They seek out "sensitized" areas—grain boundaries in the metal weakened by heat—and cause rapid, catastrophic cracking. A pipe that looked perfect yesterday can literally shatter today.
) during welding or high-temperature process operations, chromium carbides precipitate along the grain boundaries. This depletes the adjacent zones of chromium, rendering them vulnerable to localized corrosion.