Materials

1
Materials Corrosion
2
Why worry about corrosion?

• One large chemical company spent more than
  400,000 per year for corrosion maintenance in
  its sulfuric acid plants, even though the
  corrosion conditions were not considered to be
  particularly severe.

3
Why worry about corrosion?

• A refinery employing a new process developed a
  serious problem after just 16 weeks of operation
  some parts showed a corrosion loss of as much as
  1/8 inch.

4
Why worry about corrosion?

• The trend in the chemical process industries
  toward higher temperatures and pressures has made
  possible new processes or improvements in old
  processes. Higher temperatures and pressures
  usualy involve more severe corrosion conditions.
  Many of the present day operations would not have
  been possible or economical w/o the use of
  corrosion-resistant materials.

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Why Worry about Corrosion?

• Safety/Health
• Environment
• Operability
• Profitability
• Product Quality
• Appearance of Facilities/Equipment
• Badly corroded and rusted equipment in a plant
  would leave a poor impression on the observer

6
Examples of Corrosion

• Erosion-corrosion of copper water pipe (tubing)
• Chloride Stress corrosion cracking of stainless
  steels
• Chloride pitting of stainless steel
• Nitric acid attack of titanium tubing

7
Corrosive Environments

• Atmospheric
• Industrial
• Urban
• Rural
• Marine
• Water
• Seawater
• Freshwater
• Tapwater
• Treated water

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Corrosive Environments

• Soil
• Industrial commercial/institutional

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Definition of corrosion

• Is the chemical or electro-chemical reaction
  between a material usually a metal ant its
  environment that produces a deterioration of the
  material and its properties.

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Factors Influencing Corrosion

• Design, fabrication materials
• Design/configuration
• Forming, welding, heat treating
• Metallurgy, composition
• Environmental factors
• Process chemistry including
• pH
• Dissolved materials
• Salt
• Metal ions
• Gases (O2, N2, CO2, ammonia, chlorine etc.)
• Suspended matter
• Temperature
• Flow velocity
• Micro-organisms

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Types of Corrosion

• 2 Main Types
• General corrosion is the loss material over the
  entire surface, at a relatively constant rate.
  The metal is thinned fairly uniformly, without
  appreciable localized attack.
• Localized Attack is specific to certain areas of
  the material, and can take many forms.

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Forms of Localized Attack

• Pitting is corrosion that produces sites of
  localized attack that are small relative to the
  overall exposed surface area. It is the most
  common form of corrosion in aqueous environments,
  and the major cause of corrosion service failures
  in
• the chemical processing
• industry.

13
Forms of Localized Attack contd

• CREVICE CORROSION is attack at narrow spaces or
  gaps between two metal surfaces, or between a
  metal and non-metal. It can occur at cracks or
  seams in a metal, or under a washer, gasket, or
  deposit.
• Crevice corrosion results from a difference
  between the chemistry of the bulk environment and
  that in or at the crevice.

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Forms of Localized Attack contd

• BIOLOGICAL ATTACK is that which caused or
  accelerated by organisms on the affected surface.
  Fouling organic deposits may cause crevice
  corrosion, or organisms may produce chemicals
  that cause corrosion.

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• EROSION CORROSION is acceleration of material
  loss due to the combined effects of corrosion
  plus removal of material by the moving fluid.

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Forms of Localized Attack contd

• CAVITATION IMPINGEMENT is material loss due to
  collapse of voids or cavities in the fluid, due
  to pressure changes (cavitation), or due to
  impingement of liquid droplets. This may be
  strictly mechanical damage, or may
• be worsened by the effects
• of corrosion.

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S.E.M. What is it?
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Forms of Localized Attack contd

• Fretting is a process combining wear and
  corrosion in removal of material from contacting
  solid surfaces. It typically involves very small
  relative movements of the components, oxidation
  of the surfaces, and abrasion by the oxidation
  products. It often occurs between a shaft and a
  component fitted on the shaft.

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Forms of Localized Attack contd

• INTERGRANULAR ATTACK is corrosion at the
  boundaries of a metal grain, with little or no
  attack of the grain. It results in weakening of
  the metal, or separation at the grain boundary.
  (The composition and corrosion resistance of a
  metal grain varies from the surface to the
  interior.)

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Forms of localized Attack contd

• DEALLOYING ATTACK is preferential removal of one
  constituent of an alloy in a corrosive
  environment. An example is the dezincification
  of brass, in which zinc is leached from the brass
  in some aqueous streams, leaving a weak structure
  of copper and copper oxide.

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Forms of Localized Attack contd

• GALVANIC ATTACK is attack of a metal that is in
  electrical contact with a more noble metal, or a
  non-metallic conductor, in a corrosive
  environment. Examples are corrosion of copper or
  brass couple to steel in an aqueous environment
  or corrosion of a zinc coating on steel. The
  latter is done intentionally to protect the
  steel, as in roofing nails, fencing, corrugated
  galvanized sheets, etc.

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Types of Corrosion

• Environmentally-induced cracking
• Stress-corrosion cracking (SCC) is due to the
  combined effects of a corrodent and sustained
  tensile stress. SCC of AUSTENTITIC (300-series)
  stainless steels by chorides is a major problem
  in the chemical industry. SCC can
• be caused in copper alloys in
• nitrates, and in steel by caustic.

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Environmentally-induced Cracking

• CORROSION FATIGUE occurs in a cyclically loaded
  part in a corrosive environment. It occurs
• at lower stress levels or
• after fewer cycles that
• would be the case in the
• absence of the corrosive
• environment.

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Environmentally-induced Cracking

• Hydrogen-induced cracking or Embrittlement is
  reduction of the ductility or toughness of a
  metal due to the presence of atomic hydrogen. The
  hydrogen can be present due to introduction into
  the molten metal, or through absorption by the
  solid metal.

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Environmentally-induced Cracking contd

• LIQUID METAL EMBRITTLEMENT is brittle failure of
  a normally ductile metal when coated with a thin
  film of liquid metal followed by stressing in
  tension. Examples of LME may occur when steel is
  brazed, soldered, welded, or plated, or
  dip-coated with zinc, cadmium, or tin.

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Corrosion Control

• Materials selection
• Design
• Method of Operation
• Barriers/coatings
• Paint systems
• Linings e.g. rubber or plastic
• Cladding metal on metal
• Galvanizing
• Plating
• Glass/ceramic e.g. porcelain on steel
• Inhibitors
• Cathodic/Anodic Protection

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Factors affecting choice of an engineering
material
Strength
Appearance
Corrosion resistance
Materials Selection
Availability
Fabricability
Cost
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Corrosion-resistant Materials

• All materials are resistant to corrosion in some
  specific environments. For example, carbon steel
  is resistant to many process and aqueous liquids.
  It may corrode slowly or not at all. Steel is the
  main material used in chemical plant equipment.
• The term corrosion-resistant is used to refer to
  materials that resist attack in specific or
  unusually corrosive environments.

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Corrosion-Resistant Materials

• The following is a list of a few materials used
  in various corrosive services
• Stainless steels
• Nickel nickel alloys
• Reactive refractory metals such as tantalum,
  titanium, zirconium, their alloys
• Copper/copper alloys (brasses, bronzes)

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Corrosive-Resistant Materials

• Aluminum
• Lead
• Chromium
• Plastics, such as teflon, PVC, nylon,
  polypropylene, polyethylene, etc.
• Rubbers/elastomers such as nitrile (NBR or
  BUNA-N) EPDM (e.g. NORDEL), Viton, NEOPRENE,
  butyl, etc.
• COMPOSITES, e.g. fiber-reinforced plastic (FRP,
  fiberglass)
• GLASS CERAMICS, tile, porcelain, brick

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STAINLESS STEELS

• Iron-based alloys, with at least 10.5 Chromium
• Chromium-rich oxide surface film
• passive
• Forms and heals in oxygen
• Additives of nickel, molybdenum, copper,
  titanium, aluminum, silicon, niobium, nitrogen,
  sulphur, selenium
• Processing applications, cutlery, decorative,
  health and sanitary, dairy, transportation,
  medical

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STAINLESS STEELS

• FERRITIC
• Iron plus 10-25 chromium (BCC)
• Magnetic
• High strength, limited toughness
• Good ductility fabricability
• Examples 405,409, 429, 430, 434, 442, monit

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STAINLESS STEELS

• AUSTENTITIC
• Iron plus chromium plus nickel (FCC)
• Also molybdenum, manganese, copper, nitrogen,
  others
• Non-magnetic (Usually)
• Relatively low strength
• High ductility/toughness
• Susceptible to chloride attack (SCC, pitting)
• Good fabricability
• Examples 201, 202, 205, 301, 302, 303, 304,
  304L, 305, 308, 309, 310,316, 316L, 317, 321,
  330, 347, 348, 384, 904L, nitronic types, Alloy
  20, 20Cb-3, sanicro 28

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STAINLESS STEELS

• DUPLEX
• Mixed structure of BCC ferrite FCC austenite
• High corrosion resistance, SCC-resistant
• High strength, good toughness
• Examples 329, 2205, 2507, 3RE60, 7-Mo PLUS,
  Ferralium 255

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STAINLESS STEELS

• MARTENSITIC
• Martensitic structure (distorted BCC)
• Lower chromium 10-18
• Higher carbon 0.15 min
• Magnetic, hardenable
• High strength limited toughness
• Lower corrosion resistance
• Examples 403, 410, 414, 416, 420, 431, 440

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STAINLESS STEELS

• PRECIPITATION HARDENING
• Chromium-nickel grades with copper, aluminum,
  titanium additions
• Hardened by ageing at moderately elevated
  temperatures
• Good formability (form then harden)
• Susceptible to heat damage
• Good corrosion resistance
• Examples 15-5 PH, 17-4 PH, 17-7 PH, PH 14-4 Mo,
  Custom 450, custom 455

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OTHER ALLOYS

• COPPER ITS ALLOYS
• Copper
• 99 copper
• Water service, marine, heat exchangers,
  architectural
• Not heat treatable
• Resists biofouling

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COPPER ITS ALLOYS

• BRASSES
• 5-45 Zinc
• Dealloying above 15 zinc
• Tin added to stop dealloying (admiralty and naval
  brasses)

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COPPER ITS ALLOYS

• BRONZES
• Phosphour bronze 10 tin
• Silicon bronze 1-3 Si
• Aluminum bronze 5-10 Al

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COPPER ITS ALLOYS

• CUPRO-NICKELS
• 90/10 Cu/Ni, 80/20, 70/30
• Resistant to seawater, erosion, pitting

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ALUMINUM ITS ALLOYS

• Protected by barrier oxide film
• Corrodes at low and high pH
• Resistant to nitric acid (oxidizing)
• 1xxx 99 Al
• 2xxx
• alloyed with copper
• Strong, heat-treatable
• Lower corrosion resistance

42
ALUMINUM ITS ALLOYS

• 4xxx alloyed with Si
• 5xxx Al-Mg-Mn, Al-Mg-Cr, Al-Mg-Mn-Cr

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NICKEL ITS ALLOYS

• NICKEL
• Alloy 200, commercially pure
• Plating/cladding
• Resistant to caustic
• MONEL
• Alloy 400, approx. 30 copper
• Very good fabricability

44
NICKEL ITS ALLOYS

• NICKEL-MOLY
• Hastelloy B, B-2
• Resistant to HCI
• NICKEL-CHROMIUM
• Inconel or Alloy 600
• (77 Ni-15Cr-bal Fe)

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NICKEL ITS ALLOYS

• Ni-Fe-Cr
• Incoloy or Alloy 800 (21Cr-32Ni-bal Fe)
• Resistant to chlorides
• Ni-Fe-Cr-Mo
• Includes Alloys 20 20Cb3, Incoloy 825,
  Hastelloy F G
• Increased resistance to sulphuric, phosphoric,
  and organic acids and to SCC and chloride pitting

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NICKEL ITS ALLOYS

• Ni-Cr-Mo
• Hastelloy C, C276, C-22
• Inconel or Alloy 625
• Resistant to hot acid mixtures

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NON-METALLICS

• PLASTICS
• Thermoplastics
• Polyethylene, PP, ABS, PVC, CPVC, PVDC
• Fluorocarbons PTFE or teflon, FEP, PFA, CTFE
  etc.
• Nylon
• Acetals, acrylics, polycarbonates, styrenes

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Plastics Contd

• Thermosetting resins
• Usually reinforced with glass
• Epoxy, phenolics, polyester, furanes
• Rubber Elastomers
• Synthetic natural rubbers
• Carbon graphite
• Glass
• Ceramics Refractories
• Concrete
• Wood

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METALS
MATERIAL Advantages Disadvantage
Carbon Steel Low cost, readily available, resists abrasion, standard fabrication, resists alkali Poor resistance to acids strong alkali, often causes discolouration and contamination
Stainless steel Resists most acids, reduces discolouration, available with a variety of alloys, abrasion less than mild steel Not resistant to chlorides, more expensive, fabrication more difficult, alloy materials may have catalytic effects
Monel-Nickel Little discoloration, contamination, resistant to chlorides Not resistant to oxidizing environments, expensive
Hasteloy Improved over Monel-Nickel More expensive than Monel-Nickel
Other exotic metals Improves specific properties Can be very high cost
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Non-metals
Material Advantages Disadvantage
Glass Useful in laboratory and batch system, low diffusion at walls Fragile, not resistant to high alkali, poor heat transfer, poor abrasion resistance
Plastics Good at low temperature, large variety to select from with various characteristics, easy to fabricate, seldom discolours, minor catalytic effects possible Poor at high temperature, low strength, not resistant to high alkali conditions, low heat transfer, low cost
Ceramics Withstands high temperatures, variety of formulations available, modest cost Poor abrasion properties, high diffusion at walls (in particular hydrogen), low heat transfer, may encourage catalytic reactions
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Tensile Strength of Steel
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Data in Text
In pages 168-174 of the text you can find a table
recommending specific materials for specific
chemicals, and descriptions of some common alloys
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The Methanol Project

• Process streams in the methanol section are not
  corrosive
• Sulphur can cause problems in earlier stages, but
  that is not our problem
• Long term storage (days) of methanol in carbon
  steel can cause side reactions that generate
  impurities which interfere with proper operation
  of fuel cells

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Workshop

• What material should we use for the majority of
  the equipment in the methanol reaction and
  purification section?
• What equipment requires other material?
• What would be some good choices for that material?