S8 · Grade Boundaries by Medium

Boundary of Same Medium (904L/254SMO Media and Boundary List)

List out the media, grades, and boundary conditions related to "Boundary of Same Medium": 5 typical components/processes, including recommended grades, specifications, failure reasons, and standards.

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List of materials for five parts

Part / ComponentRecommended designationSpecification / ThicknessSurfaceMain Failure ModesReference Standards
Sulfuric Acid H₂SO₄ 20–40%904L/254SMO2507 (over 50mm/a at 40%); 316L/317L severely corroded2507 corrodes over 50mm/a in 40% H₂SO₄Sulfuric Acid is not a strength of duplex stainless steel; high-molybdenum austenitic/superaustenitic required for medium to high concentrationsASTM A240; Corrosion charts
Hydrochloric Acid HCl 20%C276/C22316L perforates in 3 days; 904L not suitable for long-term use in hydrochloric acidC276 typically <0.1mm/a in HCl; 10% H₂SO₄, 80°C <0.1mm/aHydrochloric Acid requires nickel-based alloys; high-molybdenum does not equal resistance to hydrochloric acidASTM B575; Haynes data
Phosphoric Acid H₃PO₄ (pure)904L/316L/317L (mild)444/304 insufficient in hot concentrated phosphoric acidCorrosion curves: 444→304→316/317→904L904L upgrade endpoint in phosphoric acid plants; further evaluate 254SMO when Cl⁻/F⁻ presentASTM A240; corrosion maps
High chloride seawater/RO concentrate2507/254SMO316L pitting/SCC within months; narrow boundary for 2205 at high temperature and high chlorideConcentrated Salt Water Cl⁻ 60,000–80,000ppm; 2507 CPT > 50℃, PREN 41–432507 is an economical high-corrosion-resistant choice for the high-pressure section of seawater desalination; select 254SMO/6Mo when temperature or Cl⁻ exceeds.ASTM A240/A789/A182
FGD Wet Scrubbing Acid Solution2205/2507/254NM/AL-6XN304L/316L highly corrosiveSort by Corrosion Rate: 2507 < 2205 < TA2 < 316LGrade by Location: Spraying/Deaerating 2205/2507; Inlet Flue/Tower Liners 254NM/904L/AL-6XNASTM A240；DL/T 5196
Table ContentsStandard ConfigurationMaterial selection

Consider usage conditions instead of grades

  • Here are the most common grades: 904L (2), 254SMO (2), 2507 (2) —— numbers in parentheses indicate the number of affected areas, for quoting and material preparation.
  • Common sources of corrosion are chloride ions and salts (pitting, crevice corrosion) (3/5 hits).
  • In acidic media, 316L is just the start. Increase concentration and temperature with 904L / duplex (3/5 hits).

Common questions

Which stainless steel is used most in sulfuric acid/phosphoric acid/chloride acid/high chloride media?
Top 5 parts: 904L (2), 254SMO (2), 2507 (2). Specific to a part still depends on the medium and temperature, e.g., stainless steel countertops require switching from 304 to 316L when exposed to saltwater.
Where are issues most likely to occur?
Typical failure: Wet FGD acidic wash solution. By section: spray/condenser 2205/2507; inlet stack/tower liner 254NM/904L/AL-6XN; recommended grades 2205/2507/254NM/AL-6XN, specs 304L/316L for corrosion. Dry/wet interface perforation fast.

For this type of operation, specify medium concentration, temperature, and cleaning method in the design phase.

316LRelated materials and adjacent industries2205Material specificationsStainless steel fasteners: A2-70/A4-70/A4-80/D series and latest standardsStainless FastenersDuplex flanges for seawater desalination: 2205/2507 pressure-temperature-corrosion boundaryDuplex Flange & DesalinationSanitary diaphragm valves/clean valves: ASME BPE, Ra, temperature boundarySanitary Valves
Applications5
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