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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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materials of construction in the cpi

Materials of Construction in the CPI

A Continuing Story of Success

characteristics of the cpi
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
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
characteristics of chemicals produced
Characteristics of Chemicals Produced
  • Toxic (HCN, H2S)
  • Corrosive (HF, HCl, H2SO4, NaOH)
  • Flammable (Propane, Benzene)
  • Explosive (DNT, NH4NO3)
  • Carcinogenic
cpi operations
CPI Operations
  • Raw materials handling
  • Unit operations
  • Storage
  • Shipment
  • Utilities
containment is vital
Containment is Vital
  • Prevent leaks
  • Secondary containment of leak
  • Remediation of area affected
  • Replacement of defective parts
  • Disposal of contaminated product
materials of construction
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

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

example h 2 so 4 in nitration process
Example: H2SO4 in Nitration Process
  • Nitration of toluene:
  • C7H8 + 2HNO3 C7H6(NO2)2 + 2H2O
  • Sulfuric Acid ties up H2O
  • H2O + H2SO4  H2SO4•H2O
nitration of toluene
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?
chemico process
Chemico Process
  • Uses hot flue gas in countercurrent exchange
  • Acid brick + membrane
  • High silicon iron (Duriron®) or high silicon nickel (Hastelloy D®) fire tubes
problems with chemico process
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
chemetics process
Chemetics Process
  • 5 Stage vacuum evaporation process
  • Glass lined vessels
  • Tantalum heater tubes (steam)
  • Venturi steam jet + barometric condenser vacuum system
problems with chemetics process
Problems with Chemetics Process
  • Corrosion of expansion bellows (321SS+Teflon® lining)
  • Corrosion of venturi expander (Alloy 20Cb3 general thinning)
solution to chemetics problems
Solution to Chemetics Problems
  • Up[grade expansion bellows to Alloy 20Cb3
  • Upgrade venturi expander to Hastelloy B-2®
storage tanks for acid
Storage Tanks for Acid
  • Vertical cylindrical tanks
  • Carbon steel construction
  • Required to hold 72%, 93%, and 98% sulfuric acid
corrosion of steel in acid
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
conclusions from rate studies
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
design issues for acid tanks
Design Issues for Acid Tanks
  • Inlet and exit nozzles
  • Impingement onto walls of tank
  • Hydrogen grooving
  • Eliminate crevices
  • Sunny side corrosion
  • Prevent acid dilution!
sulfuric acid pipelines
Sulfuric Acid Pipelines
  • Carbon steel – heavy wall
  • Limit velocity – 2 ft/sec max
  • Limit temperature
  • Use long radius elbows
  • Minimize flow disturbances from welds
problems with c steel pipelines
Problems with C Steel Pipelines
  • Maximum velocity limits production
  • Weld roughness causes damage
  • Accelerated corrosion at inlet end
corrosion rate prediction
Corrosion Rate Prediction
  • Dissolution of iron sulfate
  • Mass transfer analogy (Chilton, Colburn)
  • Prediction confirmed by measurements
  • CR = F(T,V,,,d)[w – Fe]
  • For 72%, use Alloy 20Cb3
  • For 93 and 98%, use 316L SS
  • Reliability improved
  • Iron content of acid reduced
answer to question
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
  • Higher cost materials are often justified by improved safety and reliability
  • Newer materials solve traditional problems
  • Designs can minimize materials problems
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