2-Corrosion Rate Measurement

CORROSION RATE MEASUREMENTSCORROSION RATE MEASUREMENTS

Image source: Alabama Specialty Products, www.metalsamples.com

Basic Corrosion MeasurementsBasic 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?Mass?Weigh before, weigh afterTo 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 MeasurementsMeasurements

Size?Size?LengthLength width and/orwidth and/or thicknessthickness beforebeforeLengthLength, , 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…displacement…y qy q pp•• Sensitive enough?Sensitive enough?

M ?M ?Mass?Mass?Weigh Weigh before, weigh before, weigh afterafterToTo be of any use a weight loss measurement has to bebe of any use a weight loss measurement has to beTo 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 scaled to the size of the specimen … corrosion is a surface related phenomenon.surface related phenomenon.

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Basic Corrosion MeasurementBasic 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 thh d t ti l i t f thwhen exposed to a particular environment for a month;when exposed to a particular environment for a month;

2

mg1 corrosion Total =

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

2cm10 corrosion Total

environment in a month.environment in a month.

mg 0 1 Rate =

4

monthcm 0.1 Rate 2=


• Corrosion engineers traditionally work in units of dm2, thus:

mdm 10 monthdm

mg10

dmcm

100monthcm

mg0.1 22

2

2 =⋅

=×⋅

• BUT … even though mdms give reasonable numbers for most corrosion situations the month is a bad unit

monthdmdmmonthcm

most corrosion situations, the month is a bad unit …

• So, are often used …. mdddaydm

mg2 ⋅

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If we know the metal density we can convert the weightIf we know the metal density we can convert the weightIf we know the metal density, we can convert the weight If we know the metal density, we can convert the weight loss to “penetration”:loss to “penetration”:for for ρρ in g/cmin g/cm33: :

day/cm10x

cm100dm

mg1000g1

gcm

daydmmgx 5

2

23

2−=×××

⋅=

ρρ cm100mg1000gdaydm ⋅ ρρ

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

dyrmx

5.36yr

day365

daym

1.0x

daycm

10x 5 μ

ρμ

ρρ≡××≡−

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).

milzmyrmil

4.25z

yrm

z =μ

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

1M 2M

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Corrosion rate 1 = Corrosion rate 2 =1T

M2T2M


Often, our bit of metal ..

after exposure, looks like this …

It is covered with scale.

How would we assess corrosion under these conditions?

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Consider the scaling process…Consider the scaling process…

Weight before = Weight before = WWoo [g][g]Surface area = A Surface area = A [dm[dm22]]

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

Find condition; weight after = WFind condition; weight after = W11 [g][g]

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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 …

DescaleDescale

DescaledDescaled weight = Wweight = W22 [g][g]

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DescaledDescaled weight Wweight W22 [g][g]


⎟⎠⎞

⎜⎝⎛×

−= 2

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dmmg

g1mg1000

A)WW(

amount corrosion Total

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

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

⎠⎝dmg1A

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

221

dmg

A

)WW( 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 …

dmA

1000)562()WW(

scaleinFeoffractionA

)WW( Fe 21

scale in ×−

=

12

g1mg1000

)163()562()562(

A)WW(

Fe 21scale in ×

×+××

×−

=


221

scalein

mg)WW(700Fe

−=

The difference between iron in scale and total amount corroded

2scalein dmA

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?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 ?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”UseUse aa blankblank–– Use Use a a blankblank

–– Figure 1.24. (ASTM G1)Figure 1.24. (ASTM G1)

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SummarySummary

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

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

= 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–– mpy: average mils penetration per year, 1 mil = 0.001 inch)mpy: average mils penetration per year, 1 mil = 0.001 inch)

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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(SCC) with no detectable weight loss …

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•• For these situations, we use concepts such as For these situations, we use concepts such as crack propagation crack propagation raterate or or pit pit propagation propagation raterate..oo pp p p gp p g

•• 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,

yrmμ

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Industrial Industrial Corrosion MeasurementCorrosion Measurement

•• How would you “measure” (estimate) the corrosion of How would you “measure” (estimate) the corrosion of plant components?plant components?p pp p

•• For example:For example:–– pressure vessels or pressure tubes;pressure vessels or pressure tubes;

f d if 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 TechniqueCorrosion 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)p ( )p ( )–– 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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–– MicroscopyMicroscopy

Corrosion CouponsCorrosion Coupons

Various coupon shapes and sizesVarious coupon shapes and sizes

ASTM G58

“C” Ring – ASTM G38

20Image source: Alabama Specialty Products, www.metalsamples.com

Example: Atmospheric Exposure TestExample: Atmospheric Exposure Test

21Image source: www.corrosionsource.com

Electrochemical TechniquesElectrochemical Techniques

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Electrochemical PolarizationElectrochemical 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 perturbationg pg p–– Corrosion potential (ECorrosion potential (Ecorrcorr))–– Electrochemical noise (EN)Electrochemical noise (EN)

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Electrical Resistance (ER) MethodElectrical 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 dithi th b b dwithin the probe body.within the probe body.

AL

R ρ=A

24Image source: Alabama Specialty Products, www.metalsamples.com

ER Probe TypesER Probe Types

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Image source: (1) Alabama Specialty Products, www.metalsamples.com(2) S.Y. Li et al., Mat. Chem. Phys., 103 (2007) 9

Hydrogen Permeation MonitoringHydrogen 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.walls of vessels and piping.

26Image source: IonScience, www.ionscience.com

Hydrogen Permeation Monitoring PrinciplesHydrogen 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 toto the outside wall, leading to

Pressure increase with time withinPressure increase with time within

Pot 1 Pot 2

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

–– An electrochemical current An electrochemical current resulting from the oxidation of resulting from the oxidation of hydrogen under an appliedhydrogen under an applied

Charge Side Oxidize Side

H + e -> H+ -H + OH -> H O

+ -2

Measure Current μmA/cm2

Cathodic to produce H hydrogen under an applied hydrogen under an applied

potentialpotential–– 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.

Sample

μmA/cm2produce H

Working electrode

Ref elect

Counter electrode Solutions NaOH 1M

Devanathan-Starchurski Technique

Sample Membrane

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Surface Analysis: MicroscopySurface Analysis: Microscopy

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SEM image of a cross section of a steel specimen including an iron carbonate film.Exposed for 10 hrs at T=80oC, pH 6.6, PCO2 = 0.54 bar, Fe2+ = 250 ppm, v = 1 m/s

Surface Analysis: MicroscopySurface Analysis: Microscopy

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Radiographic InspectionRadiographic Inspection

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Standards for Corrosion TestingStandards for Corrosion TestingASTM

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 TestingA262 Practice C (Huey Test) G31 Immersion TestingA262 Practice E (Modified Strauss Test) G36 Boiling Magnesium ChlorideA380 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 TestD2240 Rubber Property Durometer Hardness G61 Cyclic PotentiodynamicD2583 Barcol Hardness G71 Galvanic Couple TestpD4340 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 TemperatureF746 Medical Implants G150 Critical Pitting TemperatureF2129 E/C Testing of Surgical ImplantsG1 Preparation, Cleaning, Evaluating Test SpecimensG3 Conventions Applicable to E/C Measurements

NACE ISO OTHERTM0169 Standard Immersion ISO 6509 Dezincification of Brass Corrositex™ Assay

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y

TM0174 Protective Coatings DuPont SW800M SSAT

TM0177 Sulfide Stress Corrosion DuPont SW1P Ferroxyl Test

TM0284 Resistance to Hydrogen Induced Cracking (HIC)

HomeworkHomework

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--443)3) Problems 1Problems 1--99

Due: Due: Next weekNext week

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2-Corrosion Rate Measurement

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