2-Corrosion Rate Measurement

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C

ORROSION

R

ATE

M

EASUREMENTS

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Basic Corrosion Measurements

If a piece of metal:

corrodes to this:

How would we know how much corrosion had occurred?

Clearly, we need before and after measurements…

Mass?

Weigh before, weigh after

To be of any use, a weight loss measurement has to be scaled to the size of the specimen … corrosion is a surface related phenomenon.

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Basic Corrosion

Basic Corrosion Measurements

Measurements

Size?

Length

Length width and/or

width and/or thickness

thickness before

before

Length

Length,

, width and/or

width and/or thickness

thickness before…

before…

•• What about after?

What about after?

Volume

Volume before and after…

before and after… by liquid

by liquid displacement…

y q

displacement…

pp

•• Sensitive enough?

Sensitive enough?

M

?

M

?

Mass?

Weigh

Weigh before, weigh

before, weigh after

after

To

To be of any use a weight loss measurement has to be

be of any use a weight loss measurement has to be

To

To be of any use, a weight loss measurement has to be

be of any use, a weight loss measurement has to be

scaled to the size of the specimen … corrosion is a

surface related phenomenon.

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Basic Corrosion Measurement

Because corrosion is a surface phenomenon, weight loss is related to Because corrosion is a surface phenomenon, weight loss is related to surface

surface area.area. For example: For example: a

a metal “coupon” having a total surface area of 10 cmmetal “coupon” having a total surface area of 10 cm22 _{loses 1}_{loses 1 mg}_mg

h d t ti l i t f th

when exposed to a particular environment for a month; when exposed to a particular environment for a month;

2

mg

1 corrosion

Total

=

which should be a characteristic amount for that metal in that which should be a characteristic amount for that metal in that

2

cm

10 corrosion

Total

environment in a month. environment in a month.

mg

0 1

Rate =

month

cm

0.1 Rate

=

₂

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Basic Corrosion Measurement

• Corrosion engineers traditionally work in units of dm

2

_,

thus:

mdm

10 month

dm

mg

10 dm

cm

100 month

cm

mg

0.1

₂ 2₂ ₂

=

⋅

=

×

⋅

• BUT … even though

mdms

give reasonable numbers for

most corrosion situations the month is a bad unit

month

dm

month

cm

most corrosion situations, the month is a bad unit …

• So, are often used ….

mdd

day

dm

mg

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Basic Corrosion Measurement

If we know the metal density we can convert the weight

If we know the metal density, we can convert the weight

loss to “penetration”:

for

for ρρ in g/cm

in g/cm

33

_:

day

/

cm

10 x

cm

100 dm

mg

1000

g

1 g

cm

day

dm

mg

x

₅ 2 2 3 2 −

=

×

⋅

=

ρ

dm ⋅

day

g

1000

mg

100 cm

ρ

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Basic Corrosion Measurement

• However, we note that 1 cm = 104 _{μm, thus:}

d

yr

m

x

5 .

36 yr

day

365 day

m

1 .

0 x

day

cm

10 x

₅

μ

ρ

μ

ρ

≡

×

≡

− A th it f i t ti (i th US) i th

• Another common unit for corrosion penetration (in the US) is the

mil … or milli-inch per year (=0.001 in/year or mpy).

mil

z

m

yr

mil

4 .

25 z

yr

m

z

μ

=

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Basic Corrosion Measurement

NOTE: these rates are averaged over the exposure time, and are quoted as if corrosion were constant with time … though it often is not …

1 M

_M

₂

Corrosion rate 1 = Corrosion rate 2 =

1 T

M

2 T

2 M

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Basic Corrosion Measurement

Often, our bit of metal ..

after exposure, looks like this …

It is covered with scale.

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Basic Corrosion Measurement

Consider the scaling process…

Weight before =

Weight before = WW_oo [g][g] Surface area = A

Surface area = A [dm[dm22_]]

Exposure time

Exposure time θθ [days][days] Exposure time =

Exposure time = θθ [days][days]

Find condition; weight after = W

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Basic Corrosion Measurement

We

We can only be sure that the remaining metal provides an can only be sure that the remaining metal provides an unequivocal reference, so …

unequivocal reference, so …

Descale Descale

Descaled

Descaled weight = Wweight = W₂₂ [g][g] Descaled

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Basic Corrosion Measurement

⎟

⎠

⎞

⎜

⎝

⎛

×

−

=

0 2 ₂

dm

mg

g

1 mg

1000

A

)

W

(

amount

corrosion

Total

((divided by divided by θθ for rate … for rate … mddmdd))

We

We also have a measure of the weight of scalealso have a measure of the weight of scale

⎠

⎝ dm

g

1 A

We

We also have a measure of the weight of scale …also have a measure of the weight of scale …

2 2 1

dm

g

A

)

W

(

scale

=

−

If

If we assume the scale is composed of we assume the scale is composed of FeFe₂₂OO₃₃, we can calculate the iron , we can calculate the iron in scale as … in scale as …

dm

A

1000

)

56

2 (

)

W

(

scale

in

Fe

of

fraction

A

)

W

(

Fe

1 2 scale in

×

−

=

g

1 mg

1000

)

16

3 (

)

56

2 (

)

56

2 (

A

)

W

(

Fe

1 2 scale in

_×

₊

_×

×

−

=

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Basic Corrosion Measurement

2 2 1 scale in

mg

)

W

(

700 Fe

=

−

The difference between iron in scale and total amount corroded

2 scale

in

dm

A

The difference between iron in scale and total amount corroded is either

– Iron released to environment… OR… – Iron deposited from environmentp

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How Do We Descale?

Chemically

Chemically or electrochemically … usually in weak or electrochemically … usually in weak acids acids ((See Table 1.2).See Table 1.2).

BUT … such

BUT … such descalingdescaling can also dissolve some of the remaining metal, can also dissolve some of the remaining metal,

h d t f thi ?

so … how do we account for this? so … how do we account for this?

–– Employ Employ an “inhibitor”an “inhibitor” Use

Use aa blankblank –– Use Use a a blankblank

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Summary

•• Simplest and most powerful technique for corrosion rate Simplest and most powerful technique for corrosion rate determination is the Weight Loss Technique

determination is the Weight Loss Technique

Corrosion Rate = mass/[(exposed surface area] · [time]) Corrosion Rate = mass/[(exposed surface area] · [time])

or or

= Average corrosion penetration depth/time = Average corrosion penetration depth/time = (mass/density/surface area/time)

= (mass/density/surface area/time) •• Common Corrosion Rate UnitsCommon Corrosion Rate Units

–– gmd: grams of metal loss per square meter per gmd: grams of metal loss per square meter per day (day (mddmdd)) / illi t t ti

/ illi t t ti

–– mm/y: average millimeters penetration per yearmm/y: average millimeters penetration per year

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Basic Corrosion

Basic Corrosion Measurement

Measurement

(Non

(Non--uniform Corrosion)

uniform Corrosion)

(Non

(Non uniform Corrosion)

uniform Corrosion)

NOTE: such corrosion measurements and units are useful for general

or uniform corrosion but they don’t work for localized corrosion (e.g. pitting or cracking). A component can fail by stress corrosion cracking (SCC) with no detectable weight loss

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Basic Corrosion Measurement

•• For these situations, we use concepts such as For these situations, we use concepts such as crack propagation crack propagation rate

rate or or oo pit pit propagation pp p p gpropagation ratep p g rate.. •• For example:For example:

““percent throughpercent through wall” for tubes pipes vessels etc ;wall” for tubes pipes vessels etc ; –– ““percent throughpercent through--wall for tubes, pipes, vessels, etc.;wall for tubes, pipes, vessels, etc.; –– “crack depth” or “pit depth” “crack depth” or “pit depth” –– usually in mil or mm; usually in mil or mm; –– “propagation rate” “propagation rate” –– etc.etc.

yr

mm

,

yr

m

μ

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Industrial

Industrial Corrosion Measurement

Corrosion Measurement

•• How would you “measure” (estimate) the corrosion of

How would you “measure” (estimate) the corrosion of

plant components?

p

•• For example:

For example:

–– pressure vessels or pressure tubes;pressure vessels or pressure tubes; f d i

f d i –– feeder pipesfeeder pipes

–– steam generator tubes; steam generator tubes;

–– feedwaterfeedwater pipes and heaters;pipes and heaters; –– etcetc..

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Corrosion Rate Measurement Technique

•• Corrosion coupon (weight loss measurement)Corrosion coupon (weight loss measurement) •• Electrochemical Electrochemical methodsmethods

–– Potentiodynamic polarization (Tafel analysis)Potentiodynamic polarization (Tafel analysis) –– Linear polarization resistance (LPR)Linear polarization resistance (LPR)pp (( ))

–– Electrochemical impedance spectroscopy (EIS)Electrochemical impedance spectroscopy (EIS) –– Corrosion potentialCorrosion potential

–– Electrochemical Electrochemical noise (EN)noise (EN)(( ))

•• NonNon--electrochemical electrochemical methodsmethods

–– Electrical resistance (ER)Electrical resistance (ER)Electrical resistance (ER)Electrical resistance (ER) –– Hydrogen monitoringHydrogen monitoring –– Chemical analysisChemical analysis –– MicroscopyMicroscopy

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Corrosion Coupons

Various coupon shapes and sizes Various coupon shapes and sizes

ASTM G58

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Example: Atmospheric Exposure Test

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Electrochemical Techniques

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Electrochemical Polarization

•• Involving large perturbationInvolving large perturbation

–– Potentiodynamic polarization (Potentiodynamic polarization (TafelTafel analysis)analysis)

•• Involving small perturbationInvolving small perturbation

–– Linear polarization resistance (LPR)Linear polarization resistance (LPR)

–– Electrochemical impedance spectroscopy (EIS)Electrochemical impedance spectroscopy (EIS)

•• Involving no perturbationInvolving no perturbationgg pp

–– Corrosion potential (ECorrosion potential (E_corr_corr)) –– Electrochemical noise (EN)Electrochemical noise (EN)

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Electrical Resistance (ER) Method

•• Measures Measures the change in electrical resistance of a corroding metal the change in electrical resistance of a corroding metal elements relative

elements relative to a reference nonto a reference non--corroding element sealed corroding element sealed ithi th b b d

ithi th b b d within the probe body. within the probe body.

A

L

R

=

ρ

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ER Probe Types

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Hydrogen Permeation Monitoring

•• The generation of atomic hydrogen, as part of the cathodic reaction The generation of atomic hydrogen, as part of the cathodic reaction in acidic environments, can be used for corrosion monitoring

in acidic environments, can be used for corrosion monitoring purposes.

purposes.

•• Hydrogen monitoring sensors are often attached to the outside Hydrogen monitoring sensors are often attached to the outside walls of vessels and piping.

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Hydrogen Permeation Monitoring Principles

•• As hydrogen passes through theAs hydrogen passes through the •• As hydrogen passes through the As hydrogen passes through the

metallic wall of the vessel it enters metallic wall of the vessel it enters a probe chamber attached tightly a probe chamber attached tightly to the outside wall, leading to to the outside wall, leading to

Pressure increase with time within Pressure increase with time within Pot 1 Pot 2

–– Pressure increase with time within Pressure increase with time within the chamber

the chamber

–– An electrochemical current An electrochemical current resulting from the oxidation of resulting from the oxidation of hydrogen under an applied hydrogen under an applied C harge Side Oxidize Side

H + e -> H+ - _{H + OH -> H O}+ -2 Measure C urrent μmA/cm2

C athodic to

p roduce H hydrogen under an applied hydrogen under an applied potential

potential

–– A current generated in an external A current generated in an external circuit, as hydrogen enters a

circuit, as hydrogen enters a miniature fuel cell.

miniature fuel cell. Samp le μmA/cm2 p roduce H Working electrode Ref elect C ounter

electrode _{Solutions NaOH 1M}

Devanathan-Starchurski Technique

Samp le Memb rane

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Surface Analysis: Microscopy

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Surface Analysis: Microscopy

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Radiographic Inspection

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Standards for Corrosion Testing

ASTM

A90/A90M Weight of Zinc Coatings G5 Potentiostatic/Potentiodynamic Anodic Polarization A262 Practice A (Oxalic Acid Etch) G28 Method A (Ferric Sulfate/Sulfuric Acid)

A262 Practice B (Streicher Test) G28 Method B (PEMT) A262 Practice C (Huey Test) G31 Immersion Testing A262 Practice C (Huey Test) G31 Immersion Testing

A262 Practice E (Modified Strauss Test) G36 Boiling Magnesium Chloride A380 Cleaning and Descaling Stainless Steels G44 Alternate Immersion Testing

A923 SSAT Duplex Stainless Steels G47 Stress Corrosion Cracking of Aluminum

B813 Liquid and Paste Fluxes for Soldering Copper G48 Method A (Ferric Chloride Pitting) B154 Mercurous Nitrate – Copper and Copper Alloys G48 Method B (Ferric Chloride Crevice)

B154 Mercurous Nitrate Copper and Copper Alloys G48 Method B (Ferric Chloride Crevice) C871 Extraction of Leachable Ions G48 Method C (Ferric Chloride Critical Pitting)

D1141 Ocean Water G48 Method D (Ferric Chloride Critical Crevice Temperature)

D1193 Reagent Water G49 Constant Load Test

D2240 Rubber Property Durometer Hardness G61 Cyclic Potentiodynamic

D2583 Barcol Hardness G71 Galvanic Couple Testp

D4340 Pressurized Hot Wall G75 Miller Wear Test

E3 Standard Metallographic Practice G102 Calculation of Corrosion Rates from E/C Measurements E45 Inclusion Content G108 E/C Reactivation for Detecting Sensitization

E112 Grain Size G123 Boiling Sodium/Calcium/Lithium Chloride F746 Medical Implants G150 Critical Pitting Temperature

F746 Medical Implants G150 Critical Pitting Temperature F2129 E/C Testing of Surgical Implants

G1 Preparation, Cleaning, Evaluating Test Specimens G3 Conventions Applicable to E/C Measurements

NACE ISO OTHER

TM0169 Standard Immersion ISO 6509 Dezincification of Brass Corrositex™ Assayy

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Homework

1)

1) What are the four component of a corrosion cell and list five What are the four component of a corrosion cell and list five different cathodic reactions

different cathodic reactions –– DO NOT LIST FIVE METAL DO NOT LIST FIVE METAL REDUCTION REACTIONS!!! REDUCTION REACTIONS!!! REDUCTION REACTIONS!!! REDUCTION REACTIONS!!! 2) 2) Problems Problems 11--44 3) 3) Problems 1Problems 1--99 Due: