NACE SP0170-2021 (formerly RP0170) is the current standard for the Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress Corrosion Cracking During a Shutdown of Refinery Units.
This standard provides technical procedures to prevent Stress Corrosion Cracking (SCC) caused by polythionic acids (PTA) that form when sulfide scales on equipment react with moisture and oxygen during refinery downtime. Key Aspects of the 2021 Revision
Scope: Covers austenitic stainless steels (300 series) and other austenitic alloys (e.g., Alloy 600, 800, 825) used in refinery services where sulfide scales can form. Protection Methods:
Nitrogen Purging: Using dry nitrogen with a low oxygen content to exclude moisture and air.
Alkaline Wash Solutions: Neutralizing acidic components using solutions like soda ash (sodium carbonate).
Dehumidification: Maintaining low relative humidity to prevent the condensation necessary for acid formation.
Application: It is specifically used during shutdowns, turnarounds, or standby periods for equipment such as hydroprocessing units, reformers, and FCC units. Accessing the Paper
Because NACE standards are now managed under AMPP (Association for Materials Protection and Performance), the 2021 version is a protected, copyrighted document. nace sp0170 pdf 2021
Official Source: You can purchase or download the PDF through the AMPP Store.
Standard ID: The full designation is AMPP SP0170-2021 (Revised 2021-12-10).
NACE SP0170, also known as "Protection of Refinery Equipment from Corrosion," provides guidelines and practices for protecting equipment in refineries from corrosion. This standard is crucial for industries that deal with refining petroleum products, as corrosion can lead to significant safety risks, environmental hazards, and financial losses.
The 2021 annexes provide "pre-qualified" materials. For example:
This standard applies to:
The standard emphasizes the importance of safety and environmental protection. Implementing these practices correctly can prevent accidents and reduce environmental impact.
NACE SP0170 is a critical standard practice used in the petroleum refining industry to prevent Polythionic Acid Stress Corrosion Cracking (PTA SCC) NACE SP0170-2021 (formerly RP0170) is the current standard
in austenitic stainless steels and related alloys during equipment shutdowns. While the most recent major reaffirmed version is NACE SP0170-2018
, it remains the active industry guideline used through 2021 and beyond.
AMPP - The Association for Materials Protection and Performance Overview of NACE SP0170
The standard provides specific mitigation methods to protect equipment—such as heaters, tubes, and reactors—during the downtime, shutdown, and startup phases of refinery operations. PTA SCC occurs when sulfide corrosion products react with oxygen and water to form polythionic acids, which can rapidly cause cracking in sensitized austenitic alloys.
AMPP - The Association for Materials Protection and Performance Key Mitigation Strategies
Industry professionals following SP0170 typically employ one or more of the following primary protection methods: Nitrogen Purging
: Using dry nitrogen to exclude oxygen and moisture from the equipment, preventing the formation of polythionic acid. Alkaline Washing Carbon steel: Hardness ≤22 HRC (per API 6A
: Applying alkaline solutions (such as soda ash) to neutralize any acids that may have formed on the equipment surfaces. Dry Air Purging
: Maintaining a dry environment with air to ensure no liquid water is present to react with sulfur species. Material Selection
: Choosing corrosion-resistant materials or employing specific fabrication practices to reduce susceptibility to sensitization. Inspectioneering Evolution of the Standard
NACE SP0170 has a long history of updates to reflect evolving refinery practices: Polythionic Acid Stress Corrosion Cracking (PASCC)
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In the high-stakes environment of the oil and gas industry, a single drop of water can be a ticking time bomb. When that water mixes with hydrogen sulfide ($H_2S$) and stresses a piece of steel, the result is not just corrosion—it is cracking, potential failure, and catastrophic safety hazards.
For decades, engineers have relied on a specific shield against this invisible threat. In 2021, that shield was refined and re-released as NACE SP0170-2021, formally titled “Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress Corrosion Cracking During Shutdown of Refinery Equipment.”*
While the title is a mouthful, the document represents a critical evolution in industrial safety. Here is why the 2021 revision of SP0170 is one of the most important downloads for materials engineers this decade.