cocate - corrosion of pipe...

27/03/2012

COCATE - Corrosion of pipe steel

Autoclave tests for pipe steels

and coatings

X. Zhang, J. Zevenbergen, M. Spruijt

27-3-2012

Cocate meeting in Copenhagen/Titel van de

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Content

1. Introduction

2. Objective

3. Approach methods

4. Results

Corrosion of steels

Coatings on carbon steel

Impedance measurements

Cross section analysis

Pull-off test

Coatings with artificial scratches

5. Conclusions

6. Future work

1. Introduction

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Pool A

Pool B

Pool C Le Havre Rotterdam

Flue gases contain CO2, O2, SOx, NOx, H2O etc.

Pipe materials: carbon steel, stainless steel?

Questions: corrosion rate, possible solution?

Pipes

Pipelines/ships

Pipes

2. Objective

Obtain corrosion data for steels in CO2 flue gas conditions

Search for solutions (e.g. coatings)

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Why does CO2 cause corrosion?

Dry CO2 does not cause corrosion. Wet CO2 does.

CO2 + H2O → H2CO3

Fe + CO2 + H2O → FeCO3 + H2

Cathodic reactions:

2H2CO3 + 2e- → H2 + 2HCO3

-

2HCO3- + 2e- → H2 + CO3

2-

2H+ + 2e- → H2

Anodic reaction:

Fe → Fe2+ + 2e-

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3. Approach methods

Simulation: to get parameters and estimate corrosion rates

Experimental investigation: autoclave tests

Set 1 (measuring the pH value and corrosion rate for metals):

1. Stream CTPbp (CO2+ NO2, O2, N2 + H2O) (1.65 bar, 65°C )

2. Stream 7Bp (CO2 + NO2, O2, N2, SO2 + H2O) (1.2 bar, 49°C)

3. CO2 + H2O (100 bar, 60°C)

Set 2 (Testing coating performance):

Media: CO2 + 3.5% NaCl

Temperature in corrosive media Tc = 60°C

Pressure in autoclave P = 100 bar

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4. Results

4.1 Calculation using NORSOK Model 506

Empirical corrosion rate (CRt) model for carbon steel in water containing CO2 at different temperatures

and wall shear stresses (S).

t: 20 - 150°C

CRt = Kt × fCO2 0.62×(S/19) 0.146 + 0.0324 log(fCO2) × f(pH)t (mm/year)

t: 15°C

CRt = Kt × fCO2 0.36×(S/19) 0.146 + 0.0324 log(fCO2) × f(pH)t

t: 5°C

CRt = Kt × fCO2 0.36× f(pH)t

fCO2: the fugacity of CO2 in bar,

f(pH)t : pH factor at temperature t.

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Calculation using NORSOK M-506 model Pool 2_ stream CTPbp

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Pressure = 1.643 bar, Shear stress = 1 Pa, CO2 = 11.32 mole%

0

0.5

1

1.5

2

2.5

3

3.5

0 50 100 150 200

Temperature / (°C)

Co

rro

sio

n r

ate

/ (

mm

/ye

ar)

pH=4

pH=5

pH=6

mole frac CO2 0.109004 0.113150 0.000044

mole frac H2O 0.183007 0.151925 0.999943

mole frac NO2 0.000060 0.000062 0.000002

mole frac SO2 0.000000 0.000000 0.000000

mole frac N2O 0.000000 0.000000 0.000000

mole frac CO 0.000002 0.000002 0.000000

mole frac CH4 0.000000 0.000000 0.000000

mole frac O2 0.019001 0.019724 0.000000

mole frac N2 0.688926 0.715138 0.000010

Pipe inner diameter (mm) 212.7

Pipe thickness (mm) 3.2

Temperature © 64.72

Pressure (bar) 1.643

Velocity (m/s) 19.44

pH: 4.4

Corrosion rate: 2.7 mm/year

(Impurities are not considered in

the calculation.)

Molar

fraction

Vapour

phase

Aqueous

phase

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Stream Pool 4-7Bp

Pressure = 1.15 bar, Shear stress = 1 Pa, CO2 = 8.566 mole%

0

0.5

1

1.5

2

2.5

0 50 100 150 200

Temperature / (°C)

Co

rro

sio

n r

ate

/ (

mm

/ye

ar)

pH=4

pH=5

pH=6

mole frac CO2 0.084238 0.085662 0.000029

mole frac H2O 0.116490 0.101548 0.999952

mole frac NO2 0.000164 0.000167 0.000008

mole frac SO2 0.000114 0.000116 0.000002

mole frac N2O 0.000000 0.000000 0.000000

mole frac CO 0.000000 0.000000 0.000000

mole frac CH4 0.000000 0.000000 0.000000

mole frac O2 0.087870 0.089356 0.000001

mole frac N2 0.711124 0.723150 0.000008

Pipe inner diameter (mm) 901.6

Pipe thickness (mm) 6.4

Temperature © 48.83

Pressure (bar) 1.15

Velocity (m/s) 21.02

Molar

fraction

Vapour

phase

Aqueous

phase

pH: 4.5

Corrosion rate: 1.7 mm/year

(Impurities are not considered in the

calculation.)

4. Results


4.2 Experimental results

4.2.1 Corrosion of steels

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Experimental set-up

Gas mixture container

Heating system Stirring controller Autoclave

Sample mounting

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2. Corrosion of Carbon steel

S355 in flue 7Bp (1.2 bar, 49°C)

pH 5.5

Day 6: Corr rate: 0.2 mm/y

Potential

Log(C

urr

ent /A

)

Corrosion rate analysis

-0.9 -0.8 -0.7 -0.6 -0.5

V

-6

-5

-4

-3

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2. Corrosion of steels

S335 steel in the CO2 CTP gas flue solution

(1.65 bar, 65°C, pH during CO2 charging: 4.7-5.3)

Time(day) CS1 CS2 CS3 Average (mm/y)

3 0.23 0.14 0.11 0.16

4 0.29 0.20 0.11 0.20

5 0.37 0.23 0.23 0.28

6 0.41 0.29 0.19 0.30

7 0.41 0.29 0.20 0.30

Corrosion current density in CTP flue

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2.0E-05

2.5E-05

3.0E-05

3.5E-05

4.0E-05

2 3 4 5 6 7 8

Time (day)

i (A

/cm

^2) CS1

CS2

CS3

Corrosion rate

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Corrosion for carbon steel

CO2 + H2O (600ml)

100 bar 60 °C

Day 6, Corrosion rate: 0.02 mm/y

Potential

Log(C

urr

ent /A

)


-60 -40 -20 0

mV

-8

-7

-6

-5

-4

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Corrosion of stainless steel 316S

in flue 7Bp (1.2 bar, 49°C)

pH 5.5

Corr rate: 0.00005 mm/y

Potential

Log(C

urr

ent /A

)


0.0 0.2 0.4 0.6

V

-9

-8

-7

-6

-5

-4

4. Results




4.2.2 Coatings on carbon steel

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A: white,

~ 360 µm

B: off-white,

~1060 µm

C: grey,

~ 1150 µm

4. Results





4.2.3 Impedance measurements

4.2.4 Cross section analysis

4.2.5 Pull-off test

4.2.6 Coatings with artificial scratches

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Impedance plots for three coatings in the CO2 plus 3.5% NaCl at 60ºC

and 100 bar.

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After autoclave test (for 60 days)

In 3.5% NaCl solution charged with CO2 to 100 bar at

60°C

(white) (off-white) (grey)

4. Results







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Cross section analysis: coating A

delamination

The white coating showed delamination at the coating/metal interface

after the test.

After exposure for 60 days Before the test

Colour: white

Thickness: ~ 360 µm

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Cross section analysis: coating B

Off-white coating did not show delamination after the test


Colour: off-white; Thickness: ~1060 µm

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Cross section analysis: coating C

Blisters are found in the coating, but not at the coating/metal interface


Colour: grey; Thickness: ~ 1150 µm

4. Results







4.2.5 Pull-off test

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Pull-off test before and after the autoclave test

A3 before exposure,

(break in the coating)

White coating

A2 after exposure,

(break at the coating/metal

interface)

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Pull-off test

B3 before exposure,


B2 after exposure,

(break at the coating/metal

interface)

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Pull-off test

C3 before exposure,


C2 after exposure,

(break partly it the coating)

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Pull-off strength test

Sample Before exposure

(MPa)

After exposure

(MPa)

Breaking place

Coating A 22.4 4.5 coating/metal

interface

Coating B 20.1 8.4 40% coating

Coating C 10.4 9.0 In coating

4. Results







4.2.5 Pull-off test

4.2.6 Coatings with artificial scratches

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Coating with an artificial scratch

Coating A Coating B Coating C

After test in autoclave at 100bar and 60°C.

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5. Conclusions

The corrosion rates calculated using NORSOK M-506 model are higher than

that measured from experiments.

The measured corrosion rate for carbon steel S355 in the flue gas environment

is higher (about 0.3 mm/y) than in CO2 saturated water at 100 bar and 60°C

(about 0.02mm/y) within 6 days.

The stainless steel has a very low general corrosion rate in the flue gas

environment.

The off-white coating (B) performs better than the other two, which can be a

good candidate for the application in the pipes to against the CO2 corrosion.

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6. Future work

Mass loss test for carbon steel in the gas flue 7Bp

Surface analysis to check localized corrosion

Autoclave tests for coating B in different thickness

Autoclave tests for coatings on CS/SS welds to simulate the coatings

at joints of different materials.

Thank you!

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COCATE (N° Grant Agreement: 241381-2)

cocate - corrosion of pipe...

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