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%
NACE RP0391 is a standard practice developed by the National Association of Corrosion Engineers (NACE) that provides guidelines for the protection of steel pipelines and other metallic structures from corrosion using cathodic protection (CP) systems.
It is important to note that NACE/AMPP standards are copyrighted intellectual property.
: Heavy corrosion allowances (e.g., 3.18 mm or 0.125 inches) are standard practice. Stainless Steels and High Alloys nace rp 0391 pdf
Originally approved in 1991 and revised in 2001, this "Standard Practice" (SP) addresses the specific challenges of handling concentrated sulfuric acid ( H2SO4cap H sub 2 cap S cap O sub 4
) between 90% and 100% concentration by mass at ambient temperatures up to 50°C (120°F) . Originally compiled by NACE Task Group T-5A-18 and updated through the Association for Materials Protection and Performance (AMPP), this standard serves as a critical safety and mechanical reference for the chemical process industries (CPI). Managing concentrated sulfuric acid requires highly specific engineering controls due to its unique chemical anomalies, including extreme hygroscopic nature, exothermic dilution properties, and flow-velocity velocity effects.
However, this passivating layer is highly fragile and vulnerable to two main operational variables: NACE Standard RP0391-2001 - ANSI Webstore Concentrated sulfuric acid is a strong oxidizing agent,
The benefits of using NACE RP0391 include:
This electrical technique can be used to maintain the protective film on steel surfaces, significantly reducing corrosion rates in tanks and heat exchangers.
Used for subsea manifolds and tubing due to high pitting resistance. 90% to 98% Forms a protective, passive ferrous
Plant operators introduce water into a 96% acid line, causing a drop to 85%.
Note: NACE standards are now under AMPP (Association for Materials Protection and Performance). What is NACE RP0391?
Understanding the standard is one thing; applying it is another. Here are three real-world scenarios where consulting the is mandatory.