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.”

5. 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
“A chemical plant effected an anuual savings of more than $10,000 merely by changing the bolt material on some equipment from one alloy to another more resistant to the conditions involved. The cost of this change was negligible. Slight changes in the process sometimes reduce the corrosiveness of plant liquors without affecting the process itself, thus permitting the use of less expensive materials! These changes can often be made after the plant is in operation, but original preventive measures are more desirable. Corrosion difficulties can often be ‘designed out’ of equipment, and the time to do this is in the original design of the plant! It is easier and cheaper to erase lines on a drawing than to repair or replace failed equipment in a plant.

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

8. Corrosive Environments
Soil
Industrial – commercial/institutional

9. Definition of corrosion
Is the chemical or electro-chemical reaction between a material – usually a metal – ant it’s environment that produces a deterioration of the material and it’s properties.

10. 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

11. 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.

12. 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 cont’d
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.

14. Forms of Localized Attack cont’d
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.

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

16. Forms of Localized Attack cont’d
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.

17. S.E.M. What is it?

18. Forms of Localized Attack cont’d
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.

19. Forms of Localized Attack cont’d
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.)

20. Forms of localized Attack cont’d
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.

21. Forms of Localized Attack cont’d
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.

22. 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.
To increase production, the temperature of the cooling medium in a heat-exchanger system was lowered and the time required per batch decreased. Lowering the temperature of the cooling medium resulted, however, I more severe thermal gradients across the metal wall, They in turn, induced higher stresses in the metal. Stress corrosion cracking of the vessels occurred quickly, an the plant was shut down with production delayed for some time.

23. 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.

24. 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.

25. Environmentally-induced Cracking cont’d
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.

26. 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

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

28. 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.

29. 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)

30. 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

31. 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

32. 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

33. 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

34. 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

35. STAINLESS STEELS MARTENSITIC Martensitic structure (distorted BCC)
Lower chromium: %
Higher carbon: 0.15% min
Magnetic, hardenable
High strength – limited toughness
Lower corrosion resistance
Examples: 403, 410, 414, 416, 420, 431, 440

36. 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

37. OTHER ALLOYS COPPER & IT’S ALLOYS Copper 99+% copper
Water service, marine, heat exchangers, architectural
Not heat treatable
Resists biofouling

38. COPPER & IT’S ALLOYS BRASSES 5-45% Zinc Dealloying above 15% zinc
Tin added to stop dealloying (admiralty and naval brasses)

39. COPPER & IT’S ALLOYS BRONZES Phosphour bronze – 10% tin
Silicon bronze – 1-3% Si
Aluminum bronze – 5-10% Al

40. COPPER & IT’S ALLOYS CUPRO-NICKELS 90/10 Cu/Ni, 80/20, 70/30
Resistant to seawater, erosion, pitting

41. ALUMINUM & IT’S 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 & IT’S ALLOYS 4xxx – alloyed with Si
5xxx – Al-Mg-Mn, Al-Mg-Cr, Al-Mg-Mn-Cr

43. NICKEL & IT’S ALLOYS NICKEL Alloy 200, commercially pure
Plating/cladding
Resistant to caustic
MONEL
Alloy 400, approx. 30% copper
Very good fabricability

44. NICKEL & IT’S ALLOYS NICKEL-MOLY Hastelloy B, B-2 Resistant to HCI
NICKEL-CHROMIUM
Inconel or Alloy 600
(77% Ni-15%Cr-bal Fe)

45. NICKEL & IT’S 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

46. NICKEL & IT’S ALLOYS Ni-Cr-Mo Hastelloy C, C276, C-22
Inconel or Alloy 625
Resistant to hot acid mixtures

47. NON-METALLICS PLASTICS Thermoplastics
Polyethylene, PP, ABS, PVC, CPVC, PVDC
Fluorocarbons – PTFE or teflon, FEP, PFA, CTFE etc.
Nylon
Acetals, acrylics, polycarbonates, styrenes

48. Plastics Cont’d Thermosetting resins Usually reinforced with glass
Epoxy, phenolics, polyester, furanes
Rubber & Elastomers
Synthetic & natural rubbers
Carbon & graphite
Glass
Ceramics & Refractories
Concrete
Wood

49. METALS MATERIAL Advantages Disadvantage Carbon Steel Stainless 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

50. Non-metals Material Advantages Disadvantage Glass Plastics Ceramics
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
From "Analysis, Synthesis, and Design of Chemical Processes" Turton, Bailie, Whiting, Shaeiwitz

51. Tensile Strength of Steel

52. Data in Text
In pages of the text you can find a table recommending specific materials for specific chemicals, and descriptions of some common alloys

53. 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

54. 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?