The alkaline wash neutralizes any polythionic acid as soon as it forms.
NACE SP0170 is designed for times when sulfide-coated equipment is opened to the air.
A positive pressure must be maintained throughout the shutdown duration to prevent atmospheric air from leaking into the system. 2. Exclusion of Moisture (Dry Air Blanketing) nace sp0170 pdf
During operation, sulfur-containing hydrocarbon streams in refineries react with stainless steel, forming a layer of sulfide scale on the metal surface. While the unit is running, this layer is harmless. However, when the unit shuts down and is exposed to the atmosphere, two key ingredients are introduced: from air. Water ( H2Ocap H sub 2 cap O ) from moisture or condensation.
NACE SP0170 provides essential protocols for protecting austenitic stainless steels from polythionic acid stress corrosion cracking (PTA-SCC) during refinery shutdowns. The standard details mitigation strategies, including nitrogen purging, alkaline washing, and dehumidification to prevent catastrophic equipment failure caused by acid formation. The official, copyrighted PDF can be purchased through the AMPP store. The alkaline wash neutralizes any polythionic acid as
NACE SP0170-2018 focuses on the complete "shutdown" period, which it defines as encompassing not only the actual downtime but also the periods required for safely shutting down and starting up the equipment . The standard outlines three primary mitigation methods to prevent PTA SCC.
Looking for more resources on corrosion prevention? Check out our other guides on NACE MR0175 and API 570 inspection codes. However, when the unit shuts down and is
Alloys stabilized with titanium (Type 321) or niobium/columbium (Type 347) are highly recommended for high-temperature sulfur services. These stabilizing elements bind with carbon at higher temperatures than chromium, preventing chromium depletion at the grain boundaries. Note, however, that even stabilized grades can undergo sensitization under severe, long-term thermal exposure, requiring SP0170 precautions during turnarounds. Key Operational Checklist Derived from NACE SP0170
They started a pilot: two additional mobile survey runs per quarter, a log of crew observations, and a small budget for targeted temporary coupons around suspect joints. The pilot cost less than anticipated. It caught two more active corrosion sites, both small and repairable. The data showed a pattern — certain clamps near high-traffic maintenance ladders, overlooked during routine measurements, correlated with early-stage failures.
NACE SP0170 is a standard that outlines the practices and procedures for preventing and controlling corrosion in petroleum refining and petrochemical processes. The standard covers various aspects of corrosion prevention, including:
The standard outlines several acceptable protection methodologies depending on whether the equipment needs to be opened for internal inspection/maintenance or kept closed during the turnaround. 1. Exclusion of Oxygen (Nitrogen Purging)