electrochemical characterisation speeds up … problem: acceptance of brazed joints in heating...

Electrochemical

characterisation speeds up prediction of corrosion behaviour

E.W. Schuring

J.W. Hooijmans

April 2013

ECN-L--13-034

www.ecn.nl

Electrochemical characterisation

speeds up prediction of corrosion

behaviour

E.W. Schuring

J.W. Hooijmans

Environment and Energy Engineering;

Stand 48

2

• Introduction • Corrosion in real life • Why Electrochemical characterisation of corrosion • Applications

• corrosion resistance coatings • corrosion behaviour (brazed) joints

• Available electrochemical corrosion techniques • Standards • Conclusions

Content

3

Knowledge development:

Degradation processes

Monitoring

Materials

Corrosion in real life

Current status

• Unplanned failures due to

corrosion damage

GDP NL

610 billion euros

Direct annual costs

due to corrosion:

18.3 Billion Euros

(3%)

Early detection of

corrosion phenomena

Materials selection Safety

+ Environment

Knowledge processes

*20-30% reduction could be achieved using existing knowledge.

New technologies enable further reduction.

Barrier quality

4

Corrosion in real life

5

Corrosion mechanisms

Transport of H2O, O2 , NaCl corrosion products etc.

Sufficient corrosion resistant?

C: Barrier properties?

Metal

D: Uniform corrosion

followed by pitting

Me 2+ H2,OH-

Anodic and

cathodic reactions

Uniform corrosion

A: Inter- / trans-

granular corrosion

B: Pitting

• Failure prediction for end-users (more sensitive than

other methods)

• On-site electrochemical characterisation measurements

in tanks and on pipeline coatings

• Determine time dependent quality and barrier properties

of coatings

• Reduce testing time

• Get insight in acting corrosion mechanisms

Too late !!!

Unexpected failure fuel tank

6

Why electrochemicl characterisation? • Standard test methods like salt spray testing are

expensive and need long exposition times • Standard characterisation can lead to

unrightfull acceptance

7

Electrochemical Corrosion testing • Barrier properties

• Corrosion rate

• Time-to-failure prediction

• Sensors

• Development accelerated corrosion test methods

Data fitting Physical model

Re Qcoating

Rcoating Qdl

Rct

Element Freedom Value Error Error %

Re Free(+) 120 N/A N/A

Qcoating-Q Free(+) 1E-07 N/A N/A

Qcoating-n Free(+) 0.89 N/A N/A

Rcoating Free(+) 4800 N/A N/A

Qdl-Q Free(+) 1E-07 N/A N/A

Qdl-n Free(+) 0.4 N/A N/A

Rct Free(+) 0 N/A N/A

Data File:

Circuit Model File: R:\Gouwen\corrosie publiciteit\Model coa

ting.mdl

Mode: Run Simulation / Freq. Range (0.01 - 100000)

Maximum Iterations: 100

Optimization Iterations: 0

Type of Fitting: Complex

Type of Weighting: Data-Modulus

Re Qcoating

Rcoating






Data File:


ting.mdl






Re Qcoating





Data File:


ting.mdl






Z'

-Z''

PC

0 200 400 600

kohm

0

100

200

300

400

500

600

kohm

O2, H2O, Na+, Cl-, etc.

Metaal

Coating of deklaag

O2, H2O Na+,Cl- ,etc.

Na+,OH-Na+,OH- e-e-Fe2+

geleidende

paden

corrosie producten

Fe2+

e-Na+,OH-

corrosie producten

1

2

3

4

Intacte coating

Te laat!!!

Bron: M. Mobin, Malik, A.U., Materials Performance, in February 2005, 2, pp. 28-31. Lekkage olie opslag tank

degradatie

Toenem

ende coatingdegradatie

1

Z'

-Z''

Coating+epox

0 10 20 30 40

kohm

0

10

20

30

40

kohm

2

3

Methods for corrosion testing

Z'

-Z''

PC

0 200 400 600

kohm

0

100

200

300

400

500

600

kohm


Metaal

Coating of deklaag



geleidende

paden

corrosie producten

Fe2+

e-Na+,OH-

corrosie producten

1

2

3

4

Intacte coating

Te laat!!!


degradatie

Toenem


1

Z'

-Z''

Coating+epox

0 10 20 30 40

kohm

0

10

20

30

40

kohm

2

3

Z'

-Z''

PC

0 200 400 600

kohm

0

100

200

300

400

500

600

kohm


Metaal

Coating of deklaag



geleidende

paden

corrosie producten

Fe2+

e-Na+,OH-

corrosie producten

1

2

3

4

Intacte coating

Te laat!!!


degradatie

Toenem


1

Z'

-Z''

Coating+epox

0 10 20 30 40

kohm

0

10

20

30

40

kohm

2

3

8

Stepwise Dissolution Method (SDM) vs Salt spray-BLC

0102030405060708090

100

0,0 0,3 0,6 0,9 1,2 1,5

BLC

aft

er

45

day

s [%

]

Accumulated charge after 6 hours SDM [C]

7075-T6 clad CrO3 anodized - primed material

Application (SDM):

Accelerated Corrosion resistance test coatings

9

Comparison between BLC and SDM – Both show wedging of anodic coating

BLC (45 days) SDM (6 hours)

Embedding mass

Anodic coating

Aluminum substrate

Application (SDM):

Accelerated Corrosion resistance test coatings

Exp

osu

re s

ide

Re Qcoating

Rcoating Qdl

Rct






Qdl-Q Free(+) 1E-07 N/A N/A

Qdl-n Free(+) 0.4 N/A N/A

Rct Free(+) 0 N/A N/A

Data File:


ting.mdl






Re Qcoating

Rcoating






Data File:


ting.mdl






Re Qcoating





Data File:


ting.mdl






Degradation of coating

system over time

Physical interpretation Equivalent circuits

0 10000 20000 30000 40000

-40000

-30000

-20000

-10000

0

Z' Ohm cm2

Z''

Oh

m c

m2

EIS measurements of organic coating

t = 0 hourst = 24 hourst = 100 hourst = 1000 hours

10

Application (EIS):

Corrosion resistance coatings

11

Problem:

Acceptance of brazed joints in heating appliances

Experience:

Brazed joints were accepted after standard corrosion testing, Salt spray testing.

Catastrophic failure in surface due to ‘knife line’-type attack which was not recognised in standard acceptance tests

Result:

User rejects brazed joints in his application(s), although wrong material combinations were originally applied

Consequence:

Limitations in design and optimisation

Solution:

Determine corrosion mechanisms and apply accelerated tests in applicable environments comparing accepted concept and new (brazed) concept

Application (PC, OCP, SDM):

Corrosion resistance brazed joints

12



Potential

Curr

ent

M&G 316L

0 1 2

V

-8

-6

-4

-2

A

Potential

Curr

ent

M&G 316L

-1 0 1 2

V

-8

-6

-4

-2

A

BNi2-solder

AISI316L

AISI316L

BNi5-solder OCP in Chlorinated tap water @ 60°C, aerated

Not recognised in Salt Spray test

AISI316L vs BNi2 AISI316L vs BNi5

13



Coupling tests 316L vs B-Ni 5: Highly electrochemically stressed

Artificial condensate

Aerated @ 60 °C

B-Ni 2 high coupling current

B-Ni 5 very low coupling current

------: B-Ni 2

------: B-Ni 5

AISI316L vs BNi2 + AISI316L vs BNi5

Active behaviour of BNi2 corrosion

time

Curr

ent

Pote

ntial

M&G 316L vs BNi-2 + 316L vs BNi-5

0 20 40 60 80

ks

-40

-30

-20

-10

0

10

µA

-0.2

0.0

0.2

V

0 20 40 60 80

ks

time

Curr

ent

Pote

ntial

M&G 316L vs BNi-2 + 316L vs BNi-5

0 20 40 60 80

ks

-40

-30

-20

-10

0

10

µA

-0.2

0.0

0.2

V

0 20 40 60 80

ks

min

14



0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0 5 10 15 20 25

Coulo

mb/c

m2

number of cycles

accumulated Charge [Coulomb/unit area]

BNi-5-condens

BNi-5-Cl-water

las 5-condens

las 1-Cl-water

Test conditions of BNi5 brazed and laser welded joint in AISI316L: - Artificial condensate: Cl-30mg/l; NO3-300mg/l; SO4-50mg/l ( @ 85°C, (5.5h) - Chlorinated tap water: 250ppm Cl @60°C (5.5h)

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0 5 10 15 20 25

OC

P [

Vo

lts]

cycle

OCP (5 min.) after each 15 min SDM cycle

BNi-5-condens

Bni-5-Cl-water

las 5-condens

las 1-Cl-water

Stepwise Dissolution Measurement (SDM) Open Corrosion Potential (OCP)

15


Various method Corrosion measurements: – Corrosion tests to standards (ASTM, ISO; Salt Spray, Stress

Corrosion, Pitting) normally long term testing

– Electrochemical techniques (various conditions): Screening – EIS (Electrochemical Impedance Spectrometry) – ECN (Electro Chemical Noise) – PC (Polarisation Curve) – Couple test Accelerated testing – AAD (Accelarated Anodic Dissolution) – SDM (Step Wise Dissolution Measurement)

16

Corrosion measurement technique

EIS = Electrochemical Impedance Spectroscopy • Sensitive measurement technique

• Data analysis by equivalent circuit modeling

• Determining underlying physical behaviour

• Determine barrier quality in time

• Quick measurement technique (hours)

• Online monitoring possible

Typical for coating systems

Corrosion measurements: EIS


17

Corrosion resistance screening: Electro Chemical Noise = ECN

Electrochemicalinterface

Cell

part

Cell

part

Cell

part

Cell

part

Electrochemicalinterface

Cell

part

Cell

part

Cell

part

Cell

part

E

time or freq. domain

transformation

FFT / MEM

I

detrending

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.10 1.00 10.00

log f [Hz]

Rp

[O

hm

]

Rp high

Rp low

Measurement data;

Potential E + current I

Data analysis Environmental resistance


Low activity

High activity

Comparison method

18

Electro Chemical Noise = ECN

• ECN: potential (=E) and / or current (=I) fluctuations

spontaneously generated by corrosion reactions

• Current flow: magnitude indicates amount of metal loss per unit

time

• Data detrending transformation to freq. or time domain

• Calculation of polarization resistance Rp

• Rp indicator for environmental resistance (the higher the better)

Typical: Comparison materials and material batches Ranking


19

Accelerated Anodic Dissolution (AAD)

Polarization curve; corrosion rate behaviour

Potential

Lo

g (

Curr

ent)

V

A

Anodic reactions Cathodic reactions

OCP

Classic accelerating corrosion

Potential

Lo

g (

Curr

ent)

V

A

E = OCP + ∆E

icorrosion

• extremely high current too aggressive acceleration

• impossible discriminate between subtle corrosion differences

• no correlation with real corrosion mechanism(s)


20

Stepwise Dissolution Method (SDM)

SDM Stepwise Dissolution Measurement

cycle 1

n-th cycle

Method:

OCP monitoring

Potentiostatic polarization; E = OCP + ∆E

∆E = 10 mV to 30 mV

OCP monitoring

Potentiostatic polarization

• Stepwise all relevant corrosion phenomena accelerated

• No change in mechanism only acceleration

Time Results in 7-8 hours

Longer exposure times of days possible

Potential

Lo

g (

Curr

ent)

V

A

1 2 n

i1 i1 in


21

Standards

• Currently no accepted standards, ISO, CEN, ASTM or NEN, are available on electrochemical characterisation

• General applicable standards are:

• ASTM G5 - 13 Standard Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements

• ASTM G61 - 86(2009) Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys

• Standards are under construction/discussion in ISO group TC156 workgroup 11 • NEN workgroup 330040 corrosion revitalised May 2013. Acts as mirror commission

for ISO TC156 • No European TC on corrosion operational

22

Summary corrosion screening method

• ECN method fast; within 1h -1 week results depending on test method!

• Fast pre-selection of promising materials/combinations cost savings • Determining of corrosion initiation

• Determination of corrosion mechanisms and propagation • Life time predictions possible • Strong combination with metallographic post-investigation

• Ranking materials / constructions for corrosion performance

Conclusions

Thanks for your attention &

Please Visit our Stand #48

ECN

Westerduinweg 3 P.O. Box 1

1755 LE Petten 1755 ZG Petten

The Netherlands The Netherlands

T +31 88 515 49 49 [email protected]

F +31 88 515 44 80 www.ecn.nl

Erik Schuring, IWE & Jaap Hooijmans Project leader Materials Testing & Analysis ______________________ ECN T: +31 88 515 4877 | M: +31 6 23455488 e-mails: [email protected], [email protected]

24

Energy-research Centre of the Netherlands

25

Locations

Petten

Amsterdam

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Wieringerwerf

Brussels

Goirle

26

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ewab

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electrochemical characterisation speeds up … problem: acceptance of brazed joints in heating...

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