Performance Assessment of
Corrosion Prevention
Compounds Using Laboratory
Tests
L. B. Simon1, R. G. Kelly2, F. Gui2, J. M. Williams3, K. Furrow3
1S & K Technologies, Dayton, OH
2University of Virginia, Charlottesville, VA
3Luna Innovations, Charlottesville, VA
History of CPC
• Started as temporary, cheap field protection
measure
• Escalation of performance requirements
• Inhibition capabilities vs those of primer
– Leachability, solubility, potency
• Critical, shorter term reapplication needs
Objectives
• Develop test suite to assess CPC
characteristics
– Protective film formation/retention
– Active Inhibition
– Water Displacement/Wicking Ability
• Compare characteristics to performance
– Boldly exposed vs. Occluded geometry (lap
joint)
– Constant Immersion vs. Wet/Dry
Experimental Methods
• Protective film formation/retention
– Electrochemical Impedance in LJSS
• Water Displacement/Wicking Ability
– Surface thermodynamic properties
– Wicking rates into simulated lap joints
• Visual Assessment
* LJSS = 20 mM Cl-, 4 mM NO2-, 4 mM HCO3-, 2 mM F-, pHi 9
CPC Tested
CPC
Specifications
Color of
liquid
Description
Film Type
general purpose,
Dark
WDHF (hard,
heavy duty, durable,
Blue/Green
dry film)
hard film forming CPC
Amlguard
Mil-C-85054
LPS 3
BMS 3-23
BMS 3-29
Dark
yellow
Dinitrol®
AV8
BMS 3-23
BMS 3-29
Dark
Brown
Dinitrol®
AV30
none
Light
Brown
Self-healing, anti-sling WDSF (waxy,
lubricant; High VOC very thin film)
high penetration,
corrosion inhibiting
WDSF (nontacky flim)
Penetrating, corrosion
WDSF (waxy)
inhibiting
Protective Film Formation
Constant vs. Alternate Immersion
Interfacial Impedance (Mohms-cm^2)
100
AV 30 on
AA7075-T6
10
Constant Immersion
1
Alternate Immersion
0.1
0.01
0
50
100
150
Exposure Time (days)
200
250
300
Visual Assessment
Main Failure Modes
Breaching of Film
Blistering of Film
Bulk Film Loss Sometimes Observed
Intact CPC Film(AV30)
0.3
Response
0.25
0.2
Area of "Lost" Film
0.15
CPC on Pristine 7075
0.1
0.05
0
0
1000
2000
3000
Wavenumber
Area of Film Loss
Remnant Protective Film After Bulk Film Loss
4000
5000
CPC Performance Ranking
(AI Exposure to LJSS)
Amlguard
AV30
AV8
LPS3
Time-to-Failure
(days)
55
55
120
85*
% area corroded
25
3
5
0*
No. failed/Total
Exposed
Ordinal
Ranking
3/3
3/3
0/3
0/3
1
2
3
4 (best)
Prediction of 120 d Possible
After 40 d Exposure
CPC Ranking vs. Interfacial Impedance (40 Days)
CPC Ranking at 120 d
5
4
3
Amlguard
2
AV30
AV8
1
LPS3
0
0
2
4
Interfacial Impedance (Mohms.cm^2)
6
Lap Joint Studies
• Surface thermodynamics
• Wicking into lap joints
– Joint initially dry
– Joint initially wet
Surface Energies of Interfaces Shows Water
Displacement Favorable for All CPC Studied
3.5
Water/Al = 24.8 mJ/m2
2
Surface Energy (mJ/m )
3
2.5
2
1.5
1
For Boldly Exposed Surfaces
0.5
0
Amlguard
AV8
LPS3
AV30
Wicking Rates
• Joint Initially Dry
– CPC to be drawn in by capillary action
• Joint Initially Wet
– Capillary action offset by need to displace
water
CPC Introduction into Joint
1.00 in.
0.50 in.
250 µm
1.50 in.
Silica Filler
250 µm
Optical Fiber
Sensor Groove
Pool of CPC
Optical Fiber Leads
Flow front under Plexiglas,
sensor two is activated
Wicking into Dry Joints is Fast
5 sec
AV 8
Wicking into Dry Joints is Fast
60 sec
Wicking Into a Dry Joint
1.00 in.
Time to Sensor, sec.
500
0.50 in.
400
0.5 in.
300
1.50 in.
1.0 in.
1.5 in.
200
100
0
Amlguard
LPS3
AV8
AV30
Wicking Capability: Amlguard > AV8 & LPS3 > AV30
CPC Wicking into Wet Joint
Slow, Non-uniform
t = 4 min
AV8
CPC Wicking into Wet Joint
Slow, Non-uniform
t = 15 min
CPC Wicking into Wet Joint
Slow, Non-uniform
t = 40 min
CPC Wicking into Wet Joint
Slow, Non-uniform
t = 57 min
Wicking Into a Wet Joint is Slow
1.00 in.
10000
0.50 in.
error bars are ± one standard deviation
Time,seconds
8000
6000
1.50 in.
0.5 in.
1.0 in.
1.5 in.
4000
2000
0
Amlguard
AV8
LPS 3
AV30
Maximum time scale on dry joint data
Conclusions I
Test Method Development
• AI in LJSS provides more rapid degradation
than CI in LJSS
• Interfacial impedance can be used to assess
CPC performance
• Interfacial impedance has more limited
ability to predict CPC performance
– Can correlate impedance to ordinal ranking
Conclusions II
Water Displacement/Wicking
• Water displacement from boldly exposed
surfaces by CPC is predicted by surface
thermodynamics measurements
• Complication of capillary forces make lap
joint wicking predictions more difficult
– But rates of wicking can be measured
Conclusions III
CPC Wicking Rates into Lap Joints
• CPC ingress in dry joints very fast
– 6 to 60 mm/min
• CPC ingress in wet joints is much slower
– 1 to 5 mm/min
• Ingress is highly variable both spatially &
temporally