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Materials of Construction in the CPI

Materials of Construction in the CPI. A Continuing Story of Success. Characteristics of the CPI. Major contributor to world economy Producer of a variety of products Produces key components for many industries 200 + years and growing. Chemical Processes - Conditions.

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Materials of Construction in the CPI

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  1. Materials of Construction in the CPI A Continuing Story of Success

  2. Characteristics of the CPI • Major contributor to world economy • Producer of a variety of products • Produces key components for many industries • 200 + years and growing

  3. Chemical Processes - Conditions • Extreme temperature range: –250 to 1400°C (LH2, POX ) • Extreme pressure range: vacuum to 4000 + psi (TDA distillation, Urea synthesis) • Large volumes of materials: 1 million gallons or more

  4. Characteristics of Chemicals Produced • Toxic (HCN, H2S) • Corrosive (HF, HCl, H2SO4, NaOH) • Flammable (Propane, Benzene) • Explosive (DNT, NH4NO3) • Carcinogenic

  5. CPI Operations • Raw materials handling • Unit operations • Storage • Shipment • Utilities

  6. Containment is Vital • Prevent leaks • Secondary containment of leak • Remediation of area affected • Replacement of defective parts • Disposal of contaminated product

  7. Materials of Construction • We rely upon M/C for containment • Very few loss of containment incidents from M/C failures • Reliability has increased dramatically in the last 40 years

  8. Question: How has industry managed to achieve this in view of the difficult conditions and cost pressures?Answer: (Later)

  9. Example: H2SO4 in Nitration Process • Nitration of toluene: • C7H8 + 2HNO3 C7H6(NO2)2 + 2H2O • Sulfuric Acid ties up H2O • H2O + H2SO4  H2SO4•H2O

  10. Nitration of Toluene • Dinitrotoluene, DNT, is important urethane intermediate • Sulfuric acid regeneration is key to process economics • Thermal regeneration used • Problem: How to contain hot acid?

  11. Chemico Process • Uses hot flue gas in countercurrent exchange • Acid brick + membrane • High silicon iron (Duriron®) or high silicon nickel (Hastelloy D®) fire tubes

  12. Problems with Chemico Process • Tubes often fracture – brittle material + thermal shock • Brick lining is difficult to maintain • Process is inefficient • Acid mist in exit gas pollutes

  13. Chemetics Process • 5 Stage vacuum evaporation process • Glass lined vessels • Tantalum heater tubes (steam) • Venturi steam jet + barometric condenser vacuum system

  14. Problems with Chemetics Process • Corrosion of expansion bellows (321SS+Teflon® lining) • Corrosion of venturi expander (Alloy 20Cb3 general thinning)

  15. Solution to Chemetics Problems • Up[grade expansion bellows to Alloy 20Cb3 • Upgrade venturi expander to Hastelloy B-2®

  16. Storage Tanks for Acid • Vertical cylindrical tanks • Carbon steel construction • Required to hold 72%, 93%, and 98% sulfuric acid

  17. Corrosion of Steel in Acid • 93% and 98% acid: H2SO4 + Fe  FeSO4(s) + H2(g) • 72% acid: • H2SO4•H2O + Fe  FeSO4•H2O(s) +H2(g) • Reactions are very fast

  18. Conclusions from Rate Studies • Corrosion rates are reasonable for all three acids • Corrosion allowance required • Corrosion rate determined by dissolution of FeSO4 • Issue of velocity accelerated corrosion • Issue of corrosion product wedging

  19. Design Issues for Acid Tanks • Inlet and exit nozzles • Impingement onto walls of tank • Hydrogen grooving • Eliminate crevices • Sunny side corrosion • Prevent acid dilution!

  20. Sulfuric Acid Pipelines • Carbon steel – heavy wall • Limit velocity – 2 ft/sec max • Limit temperature • Use long radius elbows • Minimize flow disturbances from welds

  21. Problems with C Steel Pipelines • Maximum velocity limits production • Weld roughness causes damage • Accelerated corrosion at inlet end

  22. Corrosion Rate Prediction • Dissolution of iron sulfate • Mass transfer analogy (Chilton, Colburn) • Prediction confirmed by measurements • CR = F(T,V,,,d)[w – Fe]

  23. Upgrades • For 72%, use Alloy 20Cb3 • For 93 and 98%, use 316L SS • Reliability improved • Iron content of acid reduced

  24. Answer to Question • Designs that incorporate features to prevent problems • Using industry standards (NACE, API) • Maintaining awareness of industry experience (MTI) • Inspection and upgrade to eliminate problems

  25. Conclusions • Higher cost materials are often justified by improved safety and reliability • Newer materials solve traditional problems • Designs can minimize materials problems

  26. THANK YOU! • References • Shreve,N., “The Chemical Process Industries”,McGraw-Hill, 1956 • Dillon,C.P.”M.S.for H.C.”, Vol.1 Sulfuric Acid, MTI, 1997 • NACE RP02-94 “Design, Fabrication and Inspection etc.” 1994

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