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Corrosion Basics

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January 21st, 2009 Robert J. Sinko Look for comet tails ! Water was flowing from right to left in copper water pipe. Monitoring Corrosion Visual examination for ... – PowerPoint PPT presentation

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Title: Corrosion Basics


1
Corrosion Basics
  • January 21st, 2009
  • Robert J. Sinko

2
Corrosion Experts!
  • An expert is someone who carries a briefcase and
    comes from more than 50 miles away (anonymous)
  • An expert is a man who has made all the mistakes
    which can be made in a very narrow field (Niels
    Bohr)

3
Outline of the Talk
  • A Little History
  • Corrosion Basics
  • Top Corrosion Mechanisms
  • Monitoring Corrosion and Obtaining Data
  • Materials Selection
  • Points to consider
  • Continuing Education
  • Questions

4
A Little History
  • Corrosion has been here since the copper age.
  • 18th century has Luigi Galvani and Allesandro
    Volta dabbling in electrochemistry.
  • A. Volta goes to make the 1st recorded battery or
    voltaic pile

5
A Little More History
  • Sir Humphry Davy in early 1800s passes current
    through substances to decompose them
    (electrolysis).
  • Concludes that the voltaic piles and electrolysis
    were same process.
  • Claims that current is generated only when the
    electrolyte and one of the metals was oxidized
  • Found that two metals are not required as
    reaction proceeds with zinc and carbon.
  • Initiated the use of zinc as a sacrificial anode
    for copper hulled British warships

6
A Little MORE History
  • Michael Faraday had been Sir Davys lab flunky
    but outgrew the role
  • in the 1830s he contributed by developing the
    theory of electrochemical action and coined the
    following words we use now.
  • Electrode
  • Electrolysis
  • Ion
  • Sir Davy tried to block Faradays election to the
    Royal Society
  • There are countless more that have moiled in the
    service

7
Corrosion Basics/History
  • Man sees ore in lowest energy state
  • Man transforms ore in useful object
  • Nature wants her dirt back
  • Nature transforms the object back to dirt.
  • Remember J.W. Gibbs (free energy diagram)?
  • He really worked with the 2nd Law of Thermo in
    the late 1800s.
  • (You cant break even - entropy)

8
Smelted, heated and beated, forged, ground,
drilled and machined
Useful life!
Left out in the rain
Energy
Rusted away
Ore
Time
9
Corrosion Basics
  • Corrosion is electrochemical
  • Anode (Oxidizing losing electrons) Electrode
  • Cathode (Reducing gaining electrons) Electrode
  • Need Short circuit for electrons between
    terminals
  • And need a medium for ion transport
  • Electricity and chemicals are main drivers
  • Influenced by other factors

10
Corrosion Basics
  • Usual Textbook Equations
  • Chemical Zn 2HCl ZnCl2 2H
  • Electrical Zn Zn2 2e- (anode)
  • 2H 2e- 2H (cathode)
  • Note hydrogen is atomic, not diatomic
  • This can come back to get you
  • Generally, the electrical part is not shown
  • Oxygen reaction can be inserted as well

11
Note that atomic hydrogen forms on surface and
becomes diatomic in solution. Hydrogen atoms
can be absorbed into materials (Ti and carbon
steel couple)
Figure 2.6 Electrochemical reactions occurring
during the corrosion of zinc in air-free
hydrochloric acid. Used by permission, NACE,
Corrosion Basics An Introduction, NACE, 1984, pg
28.
12
Corrosion Basics- Other Factors
  • Corrosion rates are almost initially very high
  • Polarization something to slow down reactions
  • Cathodic and anodic surface polarization
  • Film thickness of corrosion product
  • Rate of hydrogen or oxygen diffusion to and from
    surfaces
  • Rate of corrodant ion diffusion away
  • Areas of reaction (anode to cathode)
  • Oxygen Content (cathodic depolarizer)
  • Temperature every 10C 2 x corrosion rate
  • Velocity effects moving species to fro

13
Corrosion Top Mechanisms
  • General
  • Pitting
  • Crevice
  • Underdeposit
  • Dealloying
  • Galvanic
  • Enviromental Cracking
  • Stress Corrosion
  • Hydrogen Embrittlement
  • Liquid metal embrittlement
  • Corrosion Fatigue
  • Cavitation
  • Erosion

14
Corrosion Top Mechanisms General
  • The even removal of metal.
  • Allows great planning
  • Monitoring
  • Replacement and scheduling
  • Unfortunately, rare in the real world.

15
What general corrosion might look like!
16
Corrosion Top Mechanisms - Pitting
  • Most common form of localized attack
  • Break down of protective scale
  • Localized attack in break
  • Pit sets up its own environment
  • Draws in chlorides and sulfates
  • Can form caps over pits
  • Low corrosion rates are deceitful

17
Pitting corrosion small and large
18
Corrosion Top Mechanisms - Crevice
  • Much like a large area pit.
  • Occurs in cracks or crevices
  • Think of flanged connections such as
  • Piping flanges
  • Column body flanges
  • Trays on tray rings
  • Car or truck doors
  • It will also set up its own environment

19
Crevice attack on titanium from fluorinated o-ring
Severe crevice attack as well as general
20
Corrosion Top Mechanism - Underdeposit
  • Very similar to crevice corrosion but a larger
  • Usually an unplanned occurrence
  • Tools left on floor
  • River water silt buildup in bottoms
  • Sometimes called poultice corrosion
  • Sometimes called oxygen concentration cell

21
Corrosion Top Mechanism - Dealloying
  • Copper alloys
  • Brasses with gt30 zinc (bath sink tap screws)
  • Copper nickel alloys (nickel removed)
  • Cast iron (graphitization)
  • Almost any alloy can have the problem
  • Two Theories
  • One element is leached from solution
  • Both elements corroded but more noble plates
    back.

22
Brass River Water Impellor suffering from
dealloying and cavitation
23
Corrosion Mechanisms Galvanic
  • Think dry cell battery
  • Carbon center cathode
  • Zinc jacket anode
  • MnOH (manganese hydroxide paste)
  • Switch short circuit provided by your flashlight
  • Galvanized water pipe to your house
  • Powerhouse soot blower of SS nozzle and steel
    pipe
  • Over the road trailers with Al sides and steel
    rivets
  • Your water heater with aluminum sacrificial anode

24
CSTL Pipe
SS Nozzle
Soot blower metallographic sample
25
Corrosion Top Mechanisms Environmental Cracking
  • Stress Corrosion Cracking
  • Chlorides (aluminum, 300 series SS)
  • Caustic (cstl, 300 series SS, nickel alloys)
  • Ammonia (brass drain)
  • Hydrogen Embrittlement
  • Liquid Metal Embrittlement
  • Copper on stainless steel pipe
  • Zinc on stainless steel pipe

26
Weld metal
Knife line attack
Transgranular chloride SCC in 316 stainless steel
27
Intergranular caustic SCC in 304L stainless steel
finned tube.
28
If your sink at home is a nice shiny chromium
plated brass, do not pour your ammonia down this
drain and let it sit overnight. It will stress
corrosion crack! PVC/galvanized steel trap
drains go ahead no problem with ammonia.
29
Corrosion Top Mechanism Corrosion Fatigue
  • Starts with an alternating stress state
  • Protective oxide breaks open
  • Corrosive species attack and form products
  • Next cycle repeats
  • crack growth
  • more corrosion product
  • accelerated fatigue failure
  • Seen in rotating shafts

30
Corrosion fatigue, cracks can be oriented the
other direction depending on stress state of
shaft.
31
Corrosion Top Mechanisms Cavitation
  • Mostly found at
  • Pump impellor tips
  • Boat propellers
  • Constriction in fast fluids
  • Caused by formation of low pressure bubble
  • Bubble is a vacuum
  • Collapse of bubble slams the metal
  • Breaking protective oxide
  • Causing great mechanical damage

32
Piece of pump impellor with tip cavitation
Valve trim diffuser with cavitation
Centrifuge feed nozzle
33
Corrosion Top Mechanism - Erosion
  • Can be from
  • Gaseous vapor (steam cuts on flanges)
  • Liquid
  • Solids (Coal slurry)
  • Removes the protective oxide layer faster than it
    can heal

34
Look for comet tails! Water was flowing from
right to left in copper water pipe.
35
Monitoring Corrosion
  • Visual examination for leaks
  • Lab testing
  • Field testing (Corrosion racks with coupons)
  • Corrosion probes
  • ER (electrical resistance)
  • LPR (linear polarization resistance)
  • New technology
  • Metals analysis in process fluids

36
Coupons
  • All kinds of materials and shapes
  • Metals
  • Plastics
  • Fiber reinforced plastics
  • Ceramics
  • Elastomers
  • Glass
  • Homemade or store bought coupons
  • Welds
  • Heat treatments

37
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38
Corrosion Lab Testing
  • Coupons
  • Lab testing at many temps but low pressure
  • Heat flux testing to simulate exchangers
  • High pressure labs
  • Ingenious bench scale or pilot plant testing
  • Key question - What do you want to know?

39
(No Transcript)
40
Agitator blades as corrosion coupons
Weld wires as coupons
41
Field Corrosion Tools
  • Corrosion racks
  • Electrical resistance probes
  • Linear polarization resistance probes
  • New technology
  • Using electrical noise
  • LPRs
  • ERs
  • Metals analysis in solutions

42
Typical field corrosion rack for insertion
through a nozzle.
43
V IR
Electrical resistance probe
R ?l/A
44
Linear Polarization Resistance Probe
  • Gives instantaneous corrosion rates
  • Only used in conductive solutions
  • Based on the current flow between two or more
    electrodes
  • Requires the surface to become passivated (or
    polarized) and current resistance is measured.
  • Sometimes probe has a reference electrode as
    well.

45
Honeywells SmartCET uses a sensor for
background electrochemical noise to detect
pitting along with LPR probe and a sophisticated
computer program. http//hpsweb.honeywell.com/NR
/rdonlyres/8418C7B6-EBB9-4948-8441-C3803B06BA2E/44
686/ChemEngJune07.pdf
Newer Technology
46
Other Tools of the Trade
  • Electron Microscopy
  • Elemental analysis
  • Surface features
  • FTIR for identification
  • X-ray Diffraction
  • X-ray Fluorescence
  • Looking for clues by
  • Metals in fluids
  • Fluids in plastics
  • Corrosion products

47
Materials Selection
  • Basic Groups
  • Metals
  • Plastics
  • Ceramics
  • Elastomers
  • Coatings
  • Linings
  • Balance of s and -s
  • Corrosion Resistance
  • Availability
  • Mechanical Properties
  • Cost
  • Code Compliance
  • Fabricability
  • Repair options

48
Materials Selection Metals
  • Carbon steels
  • Aluminum (3000, 5000 and 6000 series)
  • Coppers, brasses, and bronzes
  • Stainless steels
  • Austenitic (200 and 300 series)
  • Martensitic (400 series)
  • Precipitation hardening (17-4 PH)
  • Duplex (2101, 2205, 255, and 2507)
  • Nickel Alloys (600 series, C, B, X, Inconel,
    Hastelloy)
  • Titanium alloys (common grades 2, 5, 7, and 11)
  • Zirconium

49
Materials Selection - Plastics
  • HDPE and Polypropylene (low end)
  • PVC and CPVC
  • Resins epoxy, vinyl esters
  • Fluoropolymers
  • PTFE, PFA, FEP, ETFE, PVDF
  • PEEK (high end)
  • Can be used as monolithic or composite pieces in
    equipment

50
Material Selection - Coatings
  • Coatings (thin or thick films)
  • Many different technologies
  • Always have holidays
  • With or without reinforcement?
  • Linings (how to anchor)
  • Whats your permeation rate?
  • Differences in thermal expansion rates
  • How do you clean?

51
Materials Selection - Ceramics
  • Concrete
  • Acid proof bricks and mortar
  • Refractory
  • Glass lined steel
  • Alumina
  • Silicon carbide
  • Silicon nitride

52
Materials Selection -Elastomers
  • Natural Rubbers
  • Nitriles
  • Neoprenes
  • Polyurethanes
  • EPDM
  • Silicones
  • Viton
  • Kalrez or Chemraz
  • Compatibility
  • Temperature limit
  • Mechanical properties
  • Availability
  • Supply Chain
  • Identification
  • Specifications

53
Gaskets Sealing
  • Gasketing has many options
  • CNA Fiber sheet gaskets (250F limit)
  • Rubber sheet goods (250F to 350F limits)
  • PTFE sheets and composites (350F limit)
  • Expanded PTFE products (600F limit)
  • Graphite gaskets (600F limit)
  • Spiral wounds (rings, windings and fillers)
  • Ring joints (for high T P)
  • Specialty materials (Thermiculite, Cogebi)

54
Know Your Service
  • Know your process conditions?
  • What are the upset conditions?
  • What are your projected lives for process?
  • What external/environmental factors?
  • How are you going to clean your equipment?

55
Corrosion ClassesContinuing Education
  • NACE has Basic Corrosion classes in Houston, TX.
  • www.nace.org is the homepage, direct link is,
  • http//web.nace.org/departments/education/Program.
    aspx?id403af18b-d51c-db11-953d-001438c08dca
  • ASM International has Corrosion Courses in Metals
    Park OH.
  • www.asminternational.org is the hompage, direct
    link is,
  • http//asmcommunity.asminternational.org/portal/si
    te/www/Education/CourseCalendar/

56
Last quote that sums it up for Corrosion!
  • ..until you return to the ground from which you
    were taken, for you are dirt and to dirt you
    shall return (Genesis 319)

57
Questions?
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