Materials of Construction in the CPI

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Materials of Construction in the CPI

• A Continuing Story of Success

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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

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Chemical Processes - Conditions

• Extreme temperature range 250 to 1400C (LH2,
  POX )
• Extreme pressure range vacuum to 4000 psi (TDA
  distillation, Urea synthesis)
• Large volumes of materials 1 million gallons or
  more

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Characteristics of Chemicals Produced

• Toxic (HCN, H2S)
• Corrosive (HF, HCl, H2SO4, NaOH)
• Flammable (Propane, Benzene)
• Explosive (DNT, NH4NO3)
• Carcinogenic

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CPI Operations

• Raw materials handling
• Unit operations
• Storage
• Shipment
• Utilities

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Containment is Vital

• Prevent leaks
• Secondary containment of leak
• Remediation of area affected
• Replacement of defective parts
• Disposal of contaminated product

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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

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

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Example H2SO4 in Nitration Process

• Nitration of toluene
• C7H8 2HNO3 ? C7H6(NO2)2 2H2O
• Sulfuric Acid ties up H2O
• H2O H2SO4 ? H2SO4H2O

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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?

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Chemico Process

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

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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

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Chemetics Process

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

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Problems with Chemetics Process

• Corrosion of expansion bellows (321SSTeflon
  lining)
• Corrosion of venturi expander (Alloy 20Cb3
  general thinning)

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Solution to Chemetics Problems

• Upgrade expansion bellows to Alloy 20Cb3
• Upgrade venturi expander to Hastelloy B-2

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Storage Tanks for Acid

• Vertical cylindrical tanks
• Carbon steel construction
• Required to hold 72, 93, and 98 sulfuric acid

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Corrosion of Steel in Acid

• 93 and 98 acid H2SO4
  Fe ? FeSO4(s) H2(g)
• 72 acid
• H2SO4H2O Fe ? FeSO4H2O(s) H2(g)
• Reactions are very fast

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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

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Design Issues for Acid Tanks

• Inlet and exit nozzles
• Impingement onto walls of tank
• Hydrogen grooving
• Eliminate crevices
• Sunny side corrosion
• Prevent acid dilution!

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Sulfuric Acid Pipelines

• Carbon steel heavy wall
• Limit velocity 2 ft/sec max
• Limit temperature
• Use long radius elbows
• Minimize flow disturbances from welds

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Problems with C Steel Pipelines

• Maximum velocity limits production
• Weld roughness causes damage
• Accelerated corrosion at inlet end

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Corrosion Rate Prediction

• Dissolution of iron sulfate
• Mass transfer analogy (Chilton, Colburn)
• Prediction confirmed by measurements
• CR F(T,V,?,?,d)w Fe

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Upgrades

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

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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

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Conclusions

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

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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