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Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 1
Laboratory Corrosion Testing: Realism and Reproducibility
with Modern Methods
Q-Lab Corporation
Watch Video Presentation
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 2
Topics
• Types of Accelerated tests
• Continuous Salt Spray (Neutral & Acidified)
• Wet/Dry Cyclic Tests
• First-Generation Cyclic Automotive Tests
• Modern Corrosion Test Methods
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 3
Types of Accelerated Tests Accelerated
Test Type Result Test Time Results compared to Research?
Development? Certification?
Quality Control Pass / fail • Defined • Short
Material specification
Certification & Research
Qualification / validation Pass / fail
• Defined • Medium-long
Reference material or specification
Certification & Development
Correlative Rank-ordered data
• Open-ended • Medium
Natural exposure (Benchmark site)
Development
Predictive Service life
Acceleration factor
• Open-ended • Long
Natural exposure (Service
environment)
Development & Warranty Contracts
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 4
Continuous Salt Spray Salt Fog Environment
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 5
Continuous Salt Spray ASTM B117
ASTM B117 is the most widely-used corrosion standard today, primarily for quality control and metallic/conversion coatings
1900 1920 1940 1960 1980 2000 2020
Method first introduced (1914)
First published by ASTM (1939)
Adopted as U.S. national standard (1964)
Year
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 6
Continuous Salt Spray ASTM B117
• 5% NaCl salt fog at 35°C
• Neutral pH
• Fine mist (atomized with compressed air) sprayed indirectly onto specimens
• ISO 9227 contains the same test
• When correctly followed, test has reasonable repeatability and reproducibility
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 7
Acidified Salt Fog
• Acetic Acid-Salt Spray
• CASS (ASTM B368; ISO 9227) – “Copper-Accelerated Acetic Acid-Salt Spray
• Quality control of inorganic coating systems – Copper/Nickel/Chromium or Nickel/Chromium coatings
on steel, zinc alloys, & aluminum alloys
– Anodized aluminum
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 8
Limitations of Salt Spray
• Not a good simulation of most service environments
• Typically produces different corrosion products than natural exposure
• Poor rank order correlation with outdoor corrosion
Q: What type of accelerated test is this?
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 9
Wet/Dry Cyclic Tests Salt Fog -> Dry Off
Exhaust Vent
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 10
Wet/Dry Cyclic Tests Prohesion (Protection is Adhesion)
• Alternating spray and dry-off
• Development began in England, 1960’s
• Dilute NaCl, (NH₄)₂SO₄
• American Architectural Manufacturers Association recently replaced ASTM B117 with this test in AAMA 2605, “Superior” coatings on aluminum
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 11
Wet/Dry Cyclic Test Case Study SSPC (Society for Protective Coatings)
• 15 different systems • Outdoor vs. accelerated
– 31 months
• Accelerated tests – Salt spray 5% – Prohesion – 2 types of cyclic immersion – Combined corrosion/
weathering
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 12
SSPC Test Results
Laboratory Test Method
Correlation w/Severe Marine Environment
Conventional Salt Spray (ASTM B117) -0.11
Cyclic Test (Prohesion) -0.07
Conventional salt spray and Cyclic results were worse than random!
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 13
Combined Corrosion/Weathering
• Developed in the 1980s by Sherwin Williams • ASTM D5894 • ISO 11997-2
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 14
Combined Corrosion/Weathering
As a coating degrades from UV exposure, its ability to protect against corrosion is reduced
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 15
Corrosion / Weathering Test Conditions
1 week Prohesion • 1 hour salt fog application at 25°C
(or ambient) • 1 hour dry off at 35°C
1 week QUV exposure • 4 hours UV exposure, UVA 340,
at 60°C • 4 hours condensation (pure
water), at 50°C
Specimens are moved manually between testers
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 16
Combined Corrosion/Weathering vs Outdoors
ASTM D5894 - QUV & Q-FOG for 2000 hrs
QUV + Q-FOG ASTM D5894
27 months outdoor marine environment
Epoxy Alkyd Latex
Outdoor
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 17
SSPC Test Results Laboratory Test Method Correlation w/Severe
Marine Environment
Conventional Salt Spray -0.11 Prohesion 0.07 Cyclic Immersion Procedures 0.48 Cyclic Immersion with UV Procedure 0.61
Combined Corrosion/ Weathering Cycle 0.71
Good correlation from combined test
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 18
Repeatability/Reproducibility
Lab Technician moves specimens from one environment to another – potential source of variability
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 19
Repeatability/Reproducibility
or
Which technician runs the test?
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 20
Wet/Dry Cyclic Tests Limitations
• Poor repeatability and reproducibility
• Poor correlation in some cases – Automotive – Industrial maintenance coatings on steel
• Attempts to improve correlation & repeatability include… – Wet bottom (water retained at chamber bottom) – Changing temperature of bubble tower – Both are crude “workarounds” for poor RH control technology
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 21
First-Generation Cyclic Automotive Tests Salt Fog Dry-Off Wetting (Humid)
Wetting specimens after dry-off reinitializes corrosion
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 22
First-Generation Cyclic Automotive Tests Salt Fog Dry-Off Wetting (Humid)
GM 9540P • NaCl and CaCl2 to simulate road salts
• Solution applied by direct Spray, not Fog
• Salt spray applied intermittently in “ambient” conditions
• Use of corrosion coupons to minimize test variability
• SAE & American Iron & Steel Institute rated this method best predictor of outdoor performance in 1991
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 23
First-Generation Cyclic Automotive Tests Salt Fog Dry-Off Wetting (Humid)
VW PV1210 • Combination of three environmental stress tests • Specimens often moved from one chamber to another
JASO M609/M610 (CCT I, II) • NaCl, 5%, Neutral pH • Designed for automatic operation in a single chamber • Emphasized rapid transition times to minimize test variability • Published in 1991
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 24
PV1210 Cyclic Corrosion test
Chamber Temp (°C)
Chamber RH (%) Actual
Setpoint
Actual
Setpoint
Temp (°C) RH (%)
Time (hrs)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 25
Limitations of First Generation CCT Poor Repeatability and Reproducibility!
• Different corrosion chambers give different results
• Huge variations in corrosion rates between different metals from test to test
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 26
Corrosion rates Galvanic corrosion
Influence of relative humidity
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 27
Corrosion in Automotive, Aerospace, & Marine Applications
• Products made from metals… – Steel (bare, galvanized, stainless) – Aluminum – Magnesium alloys – others
• Organic & Inorganic Protective Coatings
• Galvanic corrosion between different metals is a big problem
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 28
Galvanic Series Magnesium
Zinc Aluminum
Cast Iron/low carbon steel Steel (low alloy)
Brass Copper Nickel
Stainless Steel (passive) Silver Gold
Platinum
Active (Anode)
Noble (Cathode)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 29
Galvanic Corrosion
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 30
Relative Humidity & Corrosion
• Corrosion accelerates once it starts – Formation of complex oxides – Wet time increases as new oxides form
• As RH changes, corrosion of Al/Steel galvanic couple changes
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 31
Automotive Tests & Road Salt
Deliquescence: the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. All soluble salts will deliquesce if the air is sufficiently humid.
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 32
Deliquescence Relative Humidity (DRH)
Salt DRH Potassium Chloride (KCl) 85%
Ammonium Sulfate (NH4)2SO4 84%
Sodium Chloride (NaCl) 76%
Sodium Nitrate (NaNO3) 74%
Magnesium Chloride (MgCl2) 33%
Calcium Chloride (CaCl2) 31%
if the environment is above this RH, a liquid salt solution will form
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 33
RH and Time of Wetness (No salt on surface)
0
10
20
30
40
50
60
70
80
90
100
Midnight 06:00 Noon 18:00 MidnightTime of Day
RH% near the surface
Wetness at surface
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 34
RH and Time of Wetness KCl (DRH = 85%)
0
10
20
30
40
50
60
70
80
90
100
Midnight 06:00 Noon 18:00 MidnightTime of Day
RH% near the surface
Wetness at surface KCl (DRH = 85%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 35
RH and Time of Wetness NaCl (DRH = 76%)
0
10
20
30
40
50
60
70
80
90
100
Midnight 06:00 Noon 18:00 MidnightTime of Day
NaCl (DRH = 76%)
RH% near the surface
Wetness at surface KCl (DRH = 85%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 36
RH and Time of Wetness CaCl2 (DRH = 31%)
0
10
20
30
40
50
60
70
80
90
100
Midnight 06:00 Noon 18:00 MidnightTime of Day
RH% near the surface
Wetness at surface
KCl (DRH = 85%) NaCl (DRH = 76%)
CaCl2 (DRH = 31%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 37
Relative Humidity and Corrosion
Condition RH Range Result
Dry ≤ 50% Very little corrosion from NaCl
Electrolytic cells around salt crystals; film formation as RH increases
50-76% • Corrosion of steel (maximum
corroded area ~70% RH) and aluminum
• AL-Steel galvanic couple broken
Uniform Electrolytic Film formation ≥76%
• Maximum cathode area for steel; deeper non-uniform corrosion
• Al corrosion in galvanic couple with steel
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 38
Relative Humidity and Corrosion Controlling Step Transition Times
Linear – Specify Time – Controller adjusts temperature & RH for linear transition
from beginning to end of ramp time
Less Than
– Specify Time – Controller attempts to achieve conditions within specified
time
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 39
Linear Ramp Time
Temperature (°C) and RH (%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 40
“Less Than” Ramp Time
Temperature (°C) and RH (%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 41
Galvanic corrosion during ramping Low RH, <50%
0.5 hr
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8Time (hr)
Low RH – No Corrosion
Al-Steel not coupled (Steel and Al Corrode)
Al-Steel Galvanic Couple (Al Corrodes)
Full wetting
1.75 hr
3.5 hr 1.25 hr
Fast ramp
Slow ramp
RH (%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 42
Galvanic corrosion during ramping 50% < RH < 76%
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8Time (hr)
Low RH – No Corrosion
Al-Steel not coupled (Steel and Al Corrode)
Al-Steel Galvanic Couple (Al Corrodes)
Full wetting
3.5 hr 1.25 hr
Fast ramp
Slow ramp
0.5 hr 1.75 hr RH (%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 43
Galvanic corrosion during ramping High RH > 76%
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8Time (hr)
Low RH – No Corrosion
Al-Steel not coupled (Steel and Al Corrode)
Al-Steel Galvanic Couple (Al Corrodes)
Full wetting
3.5 hr 1.25 hr
Fast ramp
Slow ramp
0.5 hr 1.75 hr RH (%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 44
Galvanic corrosion during ramping High RH > 76%
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8Time (hr)
Low RH – No Corrosion
Al-Steel not coupled (Steel and Al Corrode)
Al-Steel Galvanic Couple (Al Corrodes)
Full wetting
3.5 hr 1.25 hr
Fast ramp
Slow ramp
0.5 hr 1.75 hr
Ramp Steel Corrosion (hr)
Al Corrosion (hr)
Fast 0.5 4.0
Slow 1.75 3.0
RH (%)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 45
Repeatability & Reproducibility
JASO M609 discusses transition times in the explanatory note: “The shorter the better to minimize influence to the test results.”
• One source of variability is that some chambers take longer than others to change from one test phase to the next, affecting corrosion rates
• JASO methods sought to make transitions as fast as possible to minimize variability
• This is a “workaround” to compensate for lack of RH and transition time control
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 46
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8
Temp (°C) RH (%)
Time (hours)
Fast Transition Times Designed to Improve Reproducibility Very limited time in critical RH zone of 50-90%!
Repeatability & Reproducibility
Step 1 Fog, 35 °C
Step 2 CRH: RH step, 60 °C, 25% RH CCT: Dry, 60 °C
Step 3 CRH: RH step, 50 °C, 95% RH CCT: Humid step, 60 °C
Temperature
RH
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 47
First generation cyclic automotive methods: what was missing?
• Lack of comprehensive RH control – Conditions limited to full wetting, dry,
uncontrolled room/ambient
– No control of RH transition times
– Variable specimen dry-off rates
– No RH values in critical transition zones (DRH)
• Slow application of salt solution (fog) – Little time for dry-off and re-wetting of specimens
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 48
Modern Automotive Corrosion Tests
• Salt “Fog” sometimes replaced by direct spray (Shower) – Rapid wetting with corrosive solution vs. fog – Direct spray washes off precipitated salt from previous
applications
• Controlled Relative Humidity during “ambient” phase
• Controlled Transition Times
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 49
Modern Corrosion Tests Salt Fog/Shower; Dry-Off; Controlled RH
• High volume spray wets specimens faster than traditional fog Spray volume can be controlled to adjust corrosion rates
• Precise control of Relative Humidity
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 50
Modern Automotive Corrosion Tests
Fog • Toyota TSH1555G
• VDA 621-415
• Renault D17 2028
Shower • GMW 14872
• Volvo VCS-1027, 14 & 149
• Volvo VCS 423-0014
• ISO 16701
• Ford CETP 00.00-L-467
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 51
Controlling tester environment in modern corrosion testing
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 52
Pluviometry
0
50
100
150
200
250
300
350
400
450
Fog ShowerSpray Type
Maximum Collection Rate Per Hour
Collection Rate (mL/hr)
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 53
Corrosion Coupons
• Standardized metal specimens • Mass loss due to corrosion is
measured during a test • GMW 14872 requires a specific
rate of mass loss throughout a test
• Ensures corrosion chamber is maintaining proper conditions and operator is running the test correctly
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 54
Mass Loss Tests: GMW 14872
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 55
Air Pre-Conditioner
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 56
Why the Air Pre-Conditioner is Necessary for Modern Corrosion Tests
1. Accurate control of “ambient” conditions Either the laboratory has to be perfectly controlled, or the chamber must have dehumidification
2. Accurate Ramping of Temperature & Humidity System starts with dry cool air and adds precise amounts of heat and humidity to achieve controlled conditions
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 57
0
10
20
30
40
50
60
70
80
90
100
10 15 20 25 30 35 40 45 50 55 60 65 70
RH (%)
Temperature (°C)
Without Air Preconditioner
ambient RH = 60%
With Air Preconditioner
dots represent set points of common automotive test methods
ambient Temp 23 °C
Q-FOG Operational Range
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 58
Q-FOG Operational Range
0
10
20
30
40
50
60
70
80
90
100
10 15 20 25 30 35 40 45 50 55 60 65 70
RH (%)
Temperature (°C)
ambient RH 75%
With Air Preconditioner
dots represent set points of common automotive test methods
ambient Temp 32 °C
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 59
Performance Improvement with Air Preconditioner
05
101520253035404550556065707580859095
100
0 1 2 3 4 5 6 7 8 9 10
Tem
pera
ture
(°C)
, RH
(%)
Time (hours)
No Air Preconditioner With Air Preconditioner
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 60
Conclusions • Salt spray tests are good pass/fail screening tests
• Wet/Dry tests are good comparative tests for some systems but not repeatable
• Combined weathering / corrosion cycles can provide good outdoor correlation for some materials
• First-generation cyclic automotive tests are comparative tests but not repeatable
• Modern automotive corrosion tests are more realistic and offer better repeatability and reproducibility
Laboratory Corrosion Testing: 100 Years of Progress We make testing simple 61
Thank you for your attention!
Questions?
