corrosion engineering aiche 21jan09

7/30/2019 Corrosion Engineering AIChE 21jan09

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January 21st, 2009

Robert J. Sinko


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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 mistakeswhich can be made in a very narrow field (Niels

Bohr)


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Outline of the TalkA Little History

Corrosion Basics

Top Corrosion Mechanisms Monitoring Corrosion and Obtaining Data

Materials Selection

Points to consider

Continuing Education

Questions


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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


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A Little More History

Sir Humphry Davy in early 1800s passes currentthrough substances to decompose them(electrolysis).

Concludes that the voltaic piles and electrolysiswere same process.

Claims that current is generated only when theelectrolyte and one of the metals was oxidized

Found that two metals are not required asreaction proceeds with zinc and carbon.

Initiated the use of zinc as a sacrificial anode forcopper hulled British warships


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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 ofelectrochemical action and coined the following words

we use now. Electrode

Electrolysis

Ion

Sir Davy tried to block Faradays election to the RoyalSociety

There are countless more that have moiled in theservice


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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 thelate 1800s. (You cant break even - entropy)


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Time

En

ergy

Ore

Rusted

away

Left out in the rain

Smelted, heated and

beated, forged, ground,

drilled and machined

Useful life!


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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


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Figure 2.6Electrochemical reactions occurring during the corrosion of zinc in air-free

hydrochloric acid.

Used by permission, NACE, Corrosion Basics An Introduction, NACE, 1984, pg 28.

Note that atomic hydrogen forms on

surface and becomes diatomic in solution.

Hydrogen atoms can be absorbed into

materials (Ti and carbon steel couple)


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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


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Corrosion Top Mechanisms General

Pitting

Crevice Underdeposit

Dealloying

Galvanic

Enviromental Cracking Stress Corrosion

Hydrogen Embrittlement

Liquid metal embrittlement

Corrosion Fatigue

Cavitation

Erosion


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Corrosion Top Mechanisms

General The even removal of metal.

Allows great planning

Monitoring Replacement and scheduling

Unfortunately, rare in the real world.


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What general

corrosion mightlook like!


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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


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Pitting corrosionsmall and large


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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


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Severe crevice attack as

well as general

Crevice attack on titanium

from fluorinated o-ring


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Corrosion Top Mechanism -

UnderdepositVery 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


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Dealloying Copper alloys

Brasses with >30% 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.


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Brass River Water Impellor

suffering from dealloying

and cavitation


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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


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SS NozzleCSTL

Pipe

Soot blower metallographic sample


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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


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Transgranular chloride SCC in 316 stainless steel

Weld metal

Knife line attack


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Intergranular caustic

SCC in 304L stainless

steel finned tube.


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If your sink at home is anice shiny chromium plated

brass, do not pour your

ammonia down this drain

and let it sit overnight. Itwill stress corrosion crack!

PVC/galvanized steel trap

drainsgo aheadno

problem with ammonia.


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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


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Corrosion fatigue, cracks can be oriented the other

direction depending on stress state of shaft.

C i h i


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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


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Piece of pump impellor

with tip cavitation

Valve trim diffuser with

cavitation

Centrifuge feed nozzle


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Erosion Can be from

Gaseous vapor (steam cuts on flanges)

Liquid

Solids (Coal slurry)

Removes the protective oxide layer faster than it canheal


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Look for comet tails! Water wasflowing from right to left in

copper water pipe.


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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


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CouponsAll kinds of materials and shapes

Metals

Plastics

Fiber reinforced plastics

Ceramics Elastomers

Glass

Homemade or store bought coupons

Welds Heat treatments


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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?


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Agitator blades

as corrosion

coupons

Weld wires as coupons


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Field Corrosion Tools

Corrosion racks

Electrical resistance probes

Linear polarization resistance probes

New technology Using electrical noise

LPRs

ERs

Metals analysis in solutions


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Typical field corrosion rack

for insertion through a nozzle.


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V = I*R

R = *l/A

Electricalresistance

probe


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Linear Polarization

Resistance Probe

Gives instantaneous corrosion rates

Only used in conductive solutions

Based on the current flow betweentwo or more electrodes

Requires the surface to become

passivated (or polarized) and current

resistance is measured.

Sometimes probe has a reference

electrode as well.


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Honeywells SmartCET uses a sensor

for background electrochemical noise to

detect pitting along with LPR probe and asophisticated computer program.

http://hpsweb.honeywell.com/NR/rdonlyres/8418C7B6-

EBB9-4948-8441-

C3803B06BA2E/44686/ChemEngJune07.pdf

Newer Technology

f


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Other Tools of the Trade

Electron Microscopy

Elemental analysis

Surface features

FTIR for identification

X-ray DiffractionX-ray Fluorescence

Looking for clues by

Metals in fluids

Fluids in plastics

Corrosion products


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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


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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


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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?


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Materials Selection - Ceramics Concrete

Acid proof bricks and mortar

Refractory Glass lined steel

Alumina

Silicon carbide

Silicon nitride


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Materials Selection -Elastomers Natural Rubbers

Nitriles

Neoprenes

Polyurethanes

EPDM

Silicones

Viton

Kalrez or Chemraz

Compatibility

Temperature limit

Mechanical properties

Availability

Supply Chain

Identification

Specifications


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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)


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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?


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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?id=403af18b-

d51c-db11-953d-001438c08dcaASM International has Corrosion Courses in Metals

Park OH. www.asminternational.org is the hompage, direct link is,

http://asmcommunity.asminternational.org/portal/site/www/Education/CourseCalendar/


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Last quote that sums it up for

Corrosion!

..until you return to the ground from which you weretaken, for you are dirt and to dirt you shall return(Genesis 3:19)


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corrosion engineering aiche 21jan09

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