During normal refinery operations, sulfur compounds react with iron to form metal sulfide scales inside process equipment. When the unit is shut down for maintenance, two atmospheric elements enter the system: and moisture ( H2Ocap H sub 2 cap O ) .
: The standard details the use of an aqueous solution containing soda ash (sodium carbonate, Na2CO3cap N a sub 2 cap C cap O sub 3 ) mixed with a corrosion inhibitor.
PTA SCC cannot happen during normal, reducing process operations. It requires the convergence of three factors during a turnaround or shutdown: NACE SP0170-2018
NACE SP0170 PDF 2021 has significant implications for industries that use equipment and components in petroleum refining and petrochemical environments. Some key implications include: nace sp0170 pdf 2021
What specific (e.g., 304, 316, 347) are in your unit?
Austenitic stainless steels (like Types 304 and 316) and other austenitic alloys used in high-temperature, high-pressure refinery service are often in a condition called "sensitized." This means their grain boundaries are depleted of chromium and are therefore vulnerable to attack. When PTA attacks these sensitized grain boundaries, it can initiate .
The 2018 revision (reaffirmed in later years by AMPP) applies to austenitic stainless steels and nickel alloys used in high-temperature environments. It is essential when: PTA SCC cannot happen during normal, reducing process
Engineers seeking the verified standard can purchase and download the verified standard text via legitimate industry repositories:
: This method cannot be used if workers must physically enter the vessel for internal mechanical inspections, due to asphyxiation risks. 2. Alkaline Washing (Neutralizing Acids)
This is the most common protective measure applied to equipment susceptible to PTA SCC. Austenitic stainless steels (like Types 304 and 316)
: Dehumidified air is continuously pumped through the equipment.
Polythionic acid stress corrosion cracking (PTA SCC) is a critical failure mechanism in oil refineries and petrochemical plants, particularly affecting austenitic stainless steel equipment during shutdown or startup. , often searched in the context of recent updates like "nace sp0170 pdf 2021," is the industry-standard practice providing mitigation methods for this exact problem.
This method is often preferred because it prevents the mess and potential disposal issues of an alkaline wash and can be used on catalyst beds where wetting is undesirable. C. Purging with Nitrogen (Inerting)
) break into the system, they react with these sulfide corrosion products to form polythionic acids ( H2SxO6cap H sub 2 cap S sub x cap O sub 6
AMPP - The Association for Materials Protection and Performance Overview of NACE SP0170