1

Flow Induced Corrosion in Pulping

Liquor Environments

School of Materials Science and Engineering

& Reusable Bioproducts Institute (RBI)

Georgia Institute Technology,

Atlanta, GA, USA

Preet M. Singh

Content

• Introduction

– Examples of Erosion Corrosion in Pulp Mills

• Laboratory Tests

– Rotating Cylinder Tests

• Results Under Different Pulping Liquor Conditions

– Different Alloys

– Effect of Test Temperature

– Effect of Liquor Type

• Conclusions and Mitigation Steps

2

Influence of Flow on Corrosion Reactions?

• By Transporting Reactants or Products

– Higher Flow Rate – Better Transportation – Higher Reaction Rate

• By Disruption of Passive Film at the Surface

– Film Breakdown Above Critical Velocity, Vc (Breakaway Velocity)

• Flow-Assisted Corrosion Regime

• Vc depends on alloy/environment systems

•B. Chexal, J. Horowitz, B. Dooley, P. Millett, C. Wood, R. Jones, Flow-Accelerated Corrosion in Power Plants-Revision-1,” EPRI TR-106611-R1, 1998.

Suspended Solids and Erosion Corrosion

• Flow-accelerated corrosion depends on the repassivation

kinetics and erosion rate.

– Alloy

– Environmental Parameters (pH, Temperature, Chemical Composition etc.)

– Flow Parameters

3

Flow Induced Corrosion of Cast Iron Valve

Valve in Weak Black Liquor Line

Erosion Corrosion

Hole

Erosion Corrosion in Sand Separator 2205 DSS

Courtesy – Dr. Angela Wensley

4

Flow-Induced Corrosion 2205 DSS Sand-Separator

Cone Exposed to Weak Black Liquor

Flash Tank - SS Overlaid Inlet Nozzle

Courtesy – Dr. Angela Wensley

5

Accelerated Corrosion of 2205 Duplex SS Pipe

Carrying Heavy Black Liquor

Failed DSS 2205 Pipe to Liquor Gun

6

Preferential Corrosion Attack of Austenite Grains

Black Liquor Evaporator

7

1D Evaporator

Erosion Corrosion in Evaporators – Liquor Inlet

8

Erosion Corrosion of 304L Evaporator Tubes

Upper Tube

Lower TubeJoint Between Upper and

Lower Tube

Sample used for SEM

Samples used for SEM

Erosion Corrosion Regimes for Active-Passive Alloys

Cu

rre

nt

Den

sit

y

A/c

m^

2

Potential (V)

Passive

Region

Active

CorrosionCathodic

Region

9

Effect of Particle Size – Chromium Steel in

1M NaOH (Deaerated)

Alumina Particle Size (m)

Weight Loss Rate (mg/cm2*hr)

M. M Stack et al. Wear, 256, pp 557-564, 2004

Corrosion of 304 Stainless Steel in Softwood Black

Liquors Taken From Mill-B @ 170oC

Corrosion Rate for Tensile Samples and Coupons - Mill-B

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0%

% Solids in Softwood Black Liquor

Co

rro

sio

n R

ate

(m

py

)

304 Tensile Samples

304 Coupons

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Flow Induced Corrosion or “Erosion Corrosion”

Testing in Laboratory

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 2,500 5,000 7,500 10,000

Lin

ear

Vel

oci

ty o

n E

lect

rod

e

Su

rface

(ft

/sec

RPM

Linear Velocity at the Electrode Surface vs RPM

Cylindrical Electrode and Flow in Pipe

- Erosion Corrosion Testing

Where • Ucyl (cm s–1), Target surface velocity at rotating cylinder

• Upipe (cm s–1) is flow rate in pipe

• dpipe (cm) is the diameter of the pipe,

• Sc is the Schmidt number,

• is absolute viscosity of solution in g/cm/s and

• is solution density in g/cm3.

• F is RPM of electrode

4/50857.0

28/5

7/325.0

,1185.0

pipe

pipe

cyl

electrodeCylUSc

d

dU

Using this equation:

• If water is flowing through a smooth 10-inch Schedule 40 pipe at 1.0 ft/sec,

• A Rotating Electrode with 1.2 cm diameter (and 3.0 cm2 area) rotating at 149 RPM

will match the flow conditions in that pipe

60

*,

FdU

cyl

electrodeCyl

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Corrosion Rate as a Function of Velocity - 65% solids BL

Carbon steel (516-Gr70)

Cast Iron

0.000

0.100

0.200

0.300

0.400

0.500

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Corr

osi

on

Rate

(m

m/y

ear)

Velocity (rpm)

516Gr. 70 in 65% ISC Black Liquor

23 C

60 C

90 C

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Corr

osi

on

Rate

(m

m/y

ear)

Velocity (rpm)

Cast Iron in 65% ISC Black Liquor

23 C

60 C

90 C

Corrosion Rate as a Function of Velocity in 65% solids BL

304L

316L

0.000

0.100

0.200

0.300

0.400

0.500

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Corro

sion

Rate

(m

m/y

ear)

Velocity (rpm)

316L in 65% ISC Black Liquor

23 C

60 C

90 C

0.000

0.100

0.200

0.300

0.400

0.500

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Corro

sion

Rate

(m

m/y

ear)

Velocity (rpm)

304L in 65% ISC Black Liquor

23 C

60 C

90 C

12

0.000

0.100

0.200

0.300

0.400

0.500

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Corro

sion

Ra

te (

mm

/yea

r)

Velocity (rpm)

2205 in 65% ISC Black Liquor

23 C

60 C

90 C

Corrosion Rate as a Function of Velocity in 65% solids BL

LDX 2101

DSS 2205

0.000

0.100

0.200

0.300

0.400

0.500

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Co

rro

sio

n R

ate

(m

m/y

ea

r)

Velocity (rpm)

2101 in 65% ISC Black Liquor

23 C

60 C

90 C

Critical Velocity in Different Pulping Liquors at

60oC

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Crit

ica

l V

elo

cit

y (

RP

M)

Tested at 60oC 516-Gr70CF8M Cast Steel31621012205

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Critical Velocity in Different Pulping Liquors at

90oC

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000C

rit

ica

l V

elo

cit

y (

RP

M)

Tested at 90oC 516-Gr70

CF8M Cast Steel

316

2101

2205

Conclusions - Lab Results

• Below the flow velocity of ~5 meters/sec, effect of flow on the corrosion

rate for tested materials in tested pulping liquors was negligible

• Alloys that form a stable passive film on the surface in pulping liquors

showed a critical flow rate

– Above a critical velocity range the corrosion rates for tested stainless steels

approached same order of magnitude as carbon steel

– Below critical velocity stainless steels had significantly lower corrosion rates in

tested pulping liquors, as is expected

• Cast iron had very high corrosion rate in tested pulping liquors so no

significant acceleration was seen due to flow velocity

• For carbon steel, the effect of flow on corrosion rate was gradual

compared to that for the stainless steels tested in pulping liquors

– Critical flow rate value was not clear for the C-Steel in white and green liquors

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Strategies to Mitigation Erosion Corrosion

• Modify the fluid flow (locally or globally) to minimize turbulent flow

– by either modifying the fluid flow rates or by minimizing the flow

disruptions, especially at the joints and pipe entry points

• Keep flow rates below critical flow rate

– However, data of flow conditions is not always available to make a

good decision.

– In such case, generation of data under given environment and under

realistic flow conditions should be considered, whenever possible

• Use a more corrosion resistant alloy with stable passive film in a given

environment

• If possible, other changes to environment to stabilize passive film

– Temperature, pH, Concentration, Presence of Solids

Acknowledgements

• Margaret Gorog, Subhash Pati, Phil Hardin, Jorge

Mudri, Angela Wensley and many others in the related

pulp mills for their support

• Member Companies - RBI (IPST) at Georgia Tech

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Thanks!

Questions?