NACE SP0170 is a standards-guidance document focused on welding practices for nickel-chromium-molybdenum and nickel-chromium alloys commonly used in corrosive-service equipment (e.g., sour service, hydrogen sulfide exposure). It provides recommendations to ensure weld quality, corrosion resistance, and mechanical integrity for these alloy systems when used in oil, gas, chemical, and related industries.
The NACE SP0170 standard outlines the procedures and best practices for designing, installing, and maintaining cathodic protection systems for reinforced concrete structures. Cathodic protection is a technique used to control the corrosion of metal surfaces by making them the cathode of an electrochemical cell. In the context of reinforced concrete, CP systems drive the corrosion reaction away from the steel reinforcement, thereby protecting it from corrosion.
Corrosion waits for no one. A refinery shutdown is a vulnerable time for austenitic stainless steel equipment. Without the guidance found in NACE SP0170, you risk irreversible Stress Corrosion Cracking that could lead to costly repairs or, worse, safety hazards.
Whether you are establishing a lay-up procedure for a turnaround or investigating a failure, this standard provides the roadmap you need. Don’t rely on guesswork—get the standard, study the prevention methods, and protect your assets.
Looking for more resources on corrosion prevention? Check out our other guides on NACE MR0175 and API 570 inspection codes.
The NACE SP0170 standard is a critical technical document for the petroleum refining industry, focusing on protecting equipment from Polythionic Acid Stress Corrosion Cracking (PTA SCC) during refinery shutdowns.
Originally established in 1970 and most recently updated as NACE SP0170-2018, this Standard Practice (SP) provides specific mitigation methods to safeguard austenitic stainless steels and other austenitic alloys. Overview of NACE SP0170
The standard is titled "Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress Corrosion Cracking During a Shutdown of Refinery Equipment". It is primarily intended for use by corrosion engineers, maintenance personnel, and inspection teams involved in refinery turnaround operations.
The current version, SP0170-2018, was published on September 10, 2018, by NACE International (now part of AMPP). Understanding PTA SCC
Polythionic Acid (PTA) forms when sulfide corrosion products (metal sulfides) or other sulfur species react with oxygen and water. This typically occurs during equipment shutdowns when the system is opened and exposed to the atmosphere. nace sp0170 pdf
The Risk: PTA can cause rapid, intergranular stress corrosion cracking in sensitized austenitic stainless steels.
Affected Equipment: Process units such as desulfurizers, hydrocrackers, and hydrotreaters are most at risk, though the standard applies to any refinery unit using susceptible alloys. Core Mitigation Methods in NACE SP0170
The standard outlines several primary strategies to prevent the formation of polythionic acid and the subsequent cracking:
Nitrogen Purging: Using dry nitrogen to exclude oxygen from the equipment's internal surfaces.
Alkaline Washing: Applying alkaline solutions (typically containing soda ash or sodium carbonate) to neutralize any PTA that might form.
Dry Air (Dehumidification): Maintaining a dew point at least 22°C (40°F) lower than the metal temperature to prevent the formation of liquid water.
Material Selection: Guidance on choosing resistant materials and specific fabrication practices.
Reactor Protection: Special considerations are provided for the unique challenges of protecting large reactor vessels during catalyst changes. Where to Find the NACE SP0170 PDF
As a copyrighted technical standard, official digital copies (PDF) must be purchased from authorized distributors. NACE SP0170 is a standards-guidance document focused on
AMPP Store: The official publisher's website offers the NACE SP0170-2018 for purchase.
ANSI Webstore: Provides a preview of the standard which includes the table of contents and foreword.
Accuris (formerly IHS Markit): Offers the standard in PDF and Print formats for immediate download. NACE SP0170-2018
Understanding NACE SP0170: Protection Against Polythionic Acid SCC
The NACE SP0170 standard (currently NACE SP0170-2018) is a critical standard practice for the petroleum refining industry, focusing on the protection of austenitic stainless steels and other austenitic alloys from Polythionic Acid (PTA) Stress Corrosion Cracking (SCC).
This cracking typically occurs during refinery equipment shutdowns when sulfide scale on the metal reacts with air (oxygen) and moisture (water) to form polythionic acids. Scope and Application
Target Materials: Austenitic stainless steels and iron-chromium-nickel alloys susceptible to sensitization.
Primary Industries: Refineries, specifically units like desulfurizers, hydrocrackers, and hydrotreaters where the risk of PTA SCC is high.
Other Applications: It can also be applied to crude distillation units, coking units, and fluid catalytic cracking units (FCCUs) if the user has concerns regarding PTA SCC. Key Mitigation Methods Looking for more resources on corrosion prevention
The standard outlines several strategies to prevent the formation of polythionic acid or protect the metal surface during shutdowns:
Exclusion of Oxygen: Using a dry nitrogen purge to keep air out of the equipment.
Exclusion of Water: Utilizing dry air or nitrogen to prevent liquid water from forming on surfaces.
Neutralization: Applying an alkaline wash (often using soda ash) to neutralize any PTA that might form.
Temperature Control: Keeping equipment "hot" (above the water dew point) if it remains unopened can also prevent the reaction. Document Evolution
The standard is now managed by AMPP (Association for Materials Protection and Performance), formed by the merger of NACE International and SSPC.
IHS Markit / Techstreet: These are authorized resellers of technical standards. They offer the NACE SP0170 PDF in various formats, including multi-user licenses for corporate use.
AMPP Standard Package: If your work involves multiple standards, consider purchasing the "Petroleum and Chemical Industry Standards Package," which includes SP0170 along with MR0175, SP0107, and SP0208.
The application of NACE SP0170 is vital for several reasons: