Flow Induced Corrosion in Pulping Liquor Environments

Flow Induced Corrosion in Pulping
Liquor Environments
Preet M. Singh
School of Materials Science and Engineering
& Reusable Bioproducts Institute (RBI)
Georgia Institute Technology,
Atlanta, GA, USA
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
1
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
2
Flow Induced Corrosion of Cast Iron Valve
Erosion Corrosion
Hole
Valve in Weak Black Liquor Line
Erosion Corrosion in Sand Separator 2205 DSS
Courtesy – Dr. Angela Wensley
3
Flow-Induced Corrosion 2205 DSS Sand-Separator
Cone Exposed to Weak Black Liquor
Flash Tank - SS Overlaid Inlet Nozzle
Courtesy – Dr. Angela Wensley
4
Accelerated Corrosion of 2205 Duplex SS Pipe
Carrying Heavy Black Liquor
Failed DSS 2205 Pipe to Liquor Gun
5
Preferential Corrosion Attack of Austenite Grains
Black Liquor Evaporator
6
1D Evaporator
Erosion Corrosion in Evaporators – Liquor Inlet
7
Erosion Corrosion of 304L Evaporator Tubes
Lower Tube
Joint Between Upper and
Lower Tube
Upper Tube
Sample used for
SEM
Samples used for
SEM
Current Density
A/cm^2
Erosion Corrosion Regimes for Active-Passive Alloys
Cathodic
Region
Active
Corrosion
Passive
Region
Potential (V)
8
Effect of Particle Size – Chromium Steel in
1M NaOH (Deaerated)
Weight Loss Rate (mg/cm2*hr)
Alumina Particle Size (m)
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
8.00
Corrosion Rate (mpy)
7.00
6.00
Corrosion Rate for Tensile Samples and Coupons - Mill-B
304 Tensile Samples
304 Coupons
5.00
4.00
3.00
2.00
1.00
0.00
0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0%
% Solids in Softwood Black Liquor
9
Flow Induced Corrosion or “Erosion Corrosion”
Testing in Laboratory
Linear Velocity on Electrode
Surface (ft/sec
12.00
Linear Velocity at the Electrode Surface vs RPM
10.00
8.00
6.00
4.00
2.00
0.00
0
2,500
5,000
RPM
7,500
10,000
Cylindrical Electrode and Flow in Pipe
- Erosion Corrosion Testing
U Cyl ,electrode 

U Cyl ,electrode  0.1185 

 * d cyl F
60
0.25
3/ 7
 d cyl

5/ 4
 5 / 28  Sc 0.0857U pipe
d 
 pipe 
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
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
10
Corrosion Rate as a Function of Velocity - 65% solids BL
Corrosion Rate (mm/year)
0.500
516Gr. 70 in 65% ISC Black Liquor
0.400
23 C
60 C
0.300
90 C
0.200
Cast Iron
0.100
6.0
0.000
0
1000
2000
3000
4000
5000
6000
7000
8000
Corrosion Rate (mm/year)
Velocity (rpm)
Carbon steel (516-Gr70)
Cast Iron in 65% ISC Black Liquor
9000 10000
5.0
23 C
60 C
90 C
4.0
3.0
2.0
1.0
0.0
0
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000
Velocity (rpm)
Corrosion Rate as a Function of Velocity in 65% solids BL
304L in 65% ISC Black Liquor
0.400
23 C
0.300
60 C
90 C
0.200
316L
0.100
0.500
0.000
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Velocity (rpm)
304L
Corrosion Rate (mm/year)
Corrosion Rate (mm/year)
0.500
316L in 65% ISC Black Liquor
0.400
0.300
23 C
60 C
90 C
0.200
0.100
0.000
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Velocity (rpm)
11
Corrosion Rate as a Function of Velocity in 65% solids BL
2101 in 65% ISC Black Liquor
0.400
23 C
60 C
90 C
0.300
0.200
DSS 2205
0.100
0
Corrosion Rate (mm/year)
0.500
0.000
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
0.400
Velocity (rpm)
LDX 2101
2205 in 65% ISC Black Liquor
0.300
23 C
60 C
0.200
90 C
0.100
0.000
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Velocity (rpm)
Critical Velocity in Different Pulping Liquors at
60oC
10000
9000
8000
Critical Velocity (RPM)
Corrosion Rate (mm/year)
0.500
7000
Tested at 60oC
516-Gr70
CF8M Cast Steel
316
2101
2205
6000
5000
4000
3000
2000
1000
0
12
Critical Velocity in Different Pulping Liquors at
90oC
10000
Critical Velocity (RPM)
9000
8000
7000
Tested at 90 oC
516-Gr70
CF8M Cast Steel
316
2101
2205
6000
5000
4000
3000
2000
1000
0
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
13
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
28
14
Thanks!
Questions?
15

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