Nace Rp 0391 Pdf [patched] -
Carbon steel is commonly used for storing concentrated sulfuric acid (93%-100%) because, at ambient temperatures, the acid forms a protective iron sulfate film on the metal surface. However, this film is fragile. The PDF outlines that:
Concentrated sulfuric acid is a strong oxidizing agent, but its behavior changes dramatically depending on concentration, temperature, and fluid velocity. Concentration Range Passivation Effect on Carbon Steel Risks / Mechanisms Highly corrosive; breaks down protective films quickly. Rapid uniform thinning. 90% to 98% Forms a protective, passive ferrous sulfate ( FeSO4cap F e cap S cap O sub 4 Turbulence or high flow washes away the film. 99% to 100%
: Many search engine queries for "nace rp 0391 pdf" are mistakenly submitted by refinery engineers actually looking for materials resistant to wet hydrogen sulfide (H₂S) cracking.
When carbon steel is exposed to static, ambient-temperature 93% to 98% sulfuric acid, a rapid initial reaction occurs, forming a on the metal surface. nace rp 0391 pdf
An existing pump handling 94% $H_2SO_4$ fails every six months.
: Materials like Sandvik SX provide excellent resistance across the full concentrated spectrum by forming a highly stable silicon-rich protective oxide layer. 4. Fabrication, Welding, and Equipment Engineering
The standard confirms that carbon steel is the primary material for tanks, piping, and fittings for concentrated $H_2SO_4$, provided the acid concentration remains above 90% and velocity is controlled. Carbon steel is commonly used for storing concentrated
The search for is more than just a request for a digital file—it reflects the need to prevent pipeline failures that cost millions in repairs, environmental damage, and reputational risk. This standard remains the gold standard for FRP pipeline storage, handling, installation, and repair.
: Focuses on alloys and construction materials (like carbon steel) suitable for storage tanks and piping systems in the chemical process industry (CPI). Limitations
: Updated and transitioned to a Standard Practice (SP) under AMPP (Association for Materials Protection and Performance) , which formed from the merger of NACE and SSPC. Scope Limits Concentration Range Passivation Effect on Carbon Steel Risks
Even with a PDF in hand, engineers often make these costly errors:
Before proceeding, please note that NACE RP0391 has been officially withdrawn and superseded. It was replaced by NACE SP0391 , which was later designated as AMPP SP0391 (due to the merger of NACE and SSPC into AMPP). While the PDF may still be found in older archives or referenced in legacy specifications, it is no longer the current industry standard. Always consult the latest version ( AMPP SP0391 ) for new projects.
The standard provides guidelines on monitoring corrosion through periodic inspections and thickness testing to prevent catastrophic failures. Summary of Revisions
Backfill must be sand or fine soil, pH 5–9, no sharp aggregate. What happens in reality: Native soil with limestone or slag is used to save cost. Result: point-loading stress fractures after backfill compaction.
