Applying Coatings over Flash Rust in a Marine Environment
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Transcript of Applying Coatings over Flash Rust in a Marine Environment
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Applying Coatings over Flash Rust in a Marine
Environment
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Learning Outcomes• This webinar will discuss the levels
of flash rust as defined in SSPC-SP 12, how to evaluate flash rust and the impact it can have on coating performance.
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Definitions• Flash rust
– Occurs on carbon steel from the time the waterjetting process cleans the surface to the time the water used for the cleaning process dries.
• Rust-back– Used in dry abrasive blast standards– Occurs when dry, bare steel is exposed to
conditions of high humidity, moisture, or a corrosive atmosphere.
• Rust bloom– Generic term to describe uniform rust spread
evenly over a large section of a surface
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Ultra High Pressure Waterjetting
• Method of surface preparation– May leave wet surface which can develop
flash rust • Two types of equipment
– Robotic Method• Closed Loop• Open Loop
– Hand Lance Method
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Robotic Equipment• Incorporates water removal devices• Little to no flash rust
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Hand Lance Equipment• Used to clean areas with complex shapes• Do not incorporate water removal devices• Surface tend to remain wet longer and
develop flash rust– Can blow down with air to minimize flash rust
• Flash rust may require remediation prior to painting– Wiping– Pressure washing– Abrasive blasting
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SSPC-SP 12Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating
Visible Contaminants
Flash Rust
Non-Visible Contaminants
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SSPC-SP 12Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating
• Four levels of visible contaminants– WJ-1 (Clean to Bare Substrate), WJ-2 (Substantial Cleaning),
WJ-3 (Thorough Cleaning), WJ-4 (Light Cleaning)• Four levels of flash rust
– None, Light (L), Moderate (M), Heavy (H)• Three levels of non-visible contaminants
– NV-1 (below detection limits), NV-2 (varying requirements), NV-3 (less than 50 µg/cm² of chloride or sulfate)
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Coating Over Flash Rust• Requirement depends on coating
material, performance expectations, service environment, etc.– Some products and owners allow
coatings to be applied over “Moderate” levels of flash rust
– Other products and owners only allow coating over “Light” levels or no flash rust
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Inspecting Flash Rusted Surfaces
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SSPC-SP 12Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating
Flash Rust – How do we describe this?
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SSPC-SP 12• The levels of flash rust are defined as:
– No flash rust– Light (L)
• Exhibits small quantities of a yellow-brown rust layer that is tightly adherent and not easily removed by lightly wiping with a cloth.
– Moderate (M)• Exhibits small quantities of a yellow-brown rust layer that is tightly
adherent and leaves light marks on a cloth that is lightly wiped over the surface.
– Heavy (H)• Exhibits a layer of heavy red-brown rust that hides the initial surface
condition completely and is loosely adherent, easily comes off and leaves significant marks on a cloth that is lightly wiped over the surface.
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Descriptors of Flash Rust- SSPC SP-12/VIS-4
Metric Light Moderate Heavy
Color Yellow-brown Yellow-brown Red-brown
Substrate Steel substrate may be observed
Obscures the original steel surface
Hides the initial surface condition completely
“Lightly wiping” with a cloth
Not easily removed Leaves light marks Leaves significant marks
Volume Small quantities of a…rust layer
Exhibits a layer of…rust
Exhibits a layer of heavy…rust
Distribution Evenly distributed or present in patches
Evenly distributed or present in patches
Evenly distributed or present in patches
Adhesion Tightly adherent Reasonably well adherent
Loosely adherent, easily comes off
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Descriptors of Flash Rust in SSPC-SP 12/VIS-4
Metric Light Moderate Heavy
Color Yellow-brown Yellow-brown Red-brown
Substrate Steel substrate may be observed
Obscures the original steel surface
Hides the initial surface condition completely
“Lightly wiping” with a cloth
Not easily removed Leaves light marks Leaves significant marks
Volume Small quantities of a…rust layer
Exhibits a layer of…rust
Exhibits a layer of heavy…rust
Distribution Evenly distributed or present in patches
Evenly distributed or present in patches
Evenly distributed or present in patches
Adhesion Tightly adherent Reasonably well adherent
Loosely adherent, easily comes off
What are the differences?
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Descriptors of Flash Rust in SSPC-SP 12/VIS-4
Metric Light Moderate Heavy
Color Yellow-brown Yellow-brown Red-brown
Substrate Steel substrate may be observed
Obscures the original steel surface
Hides the initial surface condition completely
“Lightly wiping” with a cloth
Not easily removed Leaves light marks Leaves significant marks
Volume Small quantities of a…rust layer
Exhibits a layer of…rust
Exhibits a layer of heavy…rust
Distribution Evenly distributed or present in patches
Evenly distributed or present in patches
Evenly distributed or present in patches
Adhesion Tightly adherent Reasonably well adherent
Loosely adherent, easily comes off
More distinct differences
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Descriptors of Flash Rust in SSPC-SP 12
Metric Light Moderate Heavy
Color Yellow-brown Yellow-brown Red-brown
Substrate Steel substrate may be observed
Obscures the original steel surface
Hides the initial surface condition completely
“Lightly wiping” with a cloth
Not easily removed Leaves light marks Leaves significant marks
Volume Small quantities of a…rust layer
Exhibits a layer of…rust
Exhibits a layer of heavy…rust
Distribution Evenly distributed or present in patches
Evenly distributed or present in patches
Evenly distributed or present in patches
Adhesion Tightly adherent Reasonably well adherent
Loosely adherent, easily comes off
Which metric takes precedence?
Some distinctions less clear
Not Quantitative
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How to Determine Level of Flash Rust• NSRP Round Robin data
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
8 6 3 4 7 1 2 5
Perc
enta
ge o
f Res
pond
ants
Test Panel Number
None Light Moderate Heavy
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Enhancements/Alternative Tests
• Recommended Guidelines for Evaluating Flash Rust (National Shipbuilding Research Program)
• “Ten Tape” Test (Hempel)• Tape Transmittance Test (U.S. Navy
Adjudication Tool)
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Recommended Guidelines forEvaluating Flash Rust
• Developed by the U.S. National Shipbuilding Research Program– Contains a table which breaks down
the flash rust definitions– Discusses impact of inspection
conditions• Time, illumination, distance
– Provides a more detailed method for performing brush-wipe test
– Discusses pressure washing for remediation
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Suggested “Brush-Cloth” Wiping Test
• Recommended to improve consistency of evaluation
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Suggested “Brush-Cloth” Wiping Test
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Removal of Flash Rust by Pressure Washing
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Hempel “Ten Tape” TestModerate Heavy
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Tape Transmittance Test• Adaptation of Hempel “10
tape” test– Apply tape to flash rust– Rub as hard as necessary with
finger– Affix tape to clear glass slide– Measure percent light
transmittance through tapes with and without flash rust
– Difference between measurements is indicative of flash rust (higher is worst)
Possible Accept/Reject Criteria
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Works with different tapesand meters
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“Light” (1-8% Change in Transmittance)
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“Moderate” (10-20% Change in Transmittance)
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“Moderate-Heavy” (14-24% Change in Transmittance)
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“Heavy” (21-50% Change in Transmittance)
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Applying Coatings Over Flash Rust
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Concerns Regarding Coating Over Flash Rust
• Flash Rust may contain contaminants– Could lead to undercutting, osmotic blistering or
loss of adhesion– Surface should be tested for non-visible
contaminants– Surface should have been thoroughly cleaned
before flash rusting begins• Flash Rust may interfere with adhesion
– Does the coating adequately wet the flash rust?– Depends on coating chemistry as well as flash
rust
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Benefit of Allowing Coating Over Flash Rust
• Reduce surface preparation cost as more flash rust is allowed– Allows operations to be sequenced more
efficiently– One source estimated savings of 20% of
typical waterjetting surface preparation cost
• Depends on extent of remediation required (e.g., complexity of structure, cleanliness requirement)
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Suitability of Flash Rust for Coating
• Several studies have shown that ultrahigh pressure waterjetting provides an excellent surface for coatings– Most agree that some level of flash rust is
acceptable for common marine quality epoxy based coating systems
– Typically either “Light” or “Moderate” is the allowable flash rust level
• Predominate concern is accurately characterization• Must be cleaned first (i.e., no “old rust”)
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Laboratory Data
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30 35 40 45
Cath
odic
Dis
bond
men
t Rad
ius
- mm
SP-10/SP-7 Light FR Moderate FR Heavy FR
• Lab testing suggests Moderate Flash Rust does not significantly impact cathodic disbondment of marine grade epoxies
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Adhesion Data from Ships In Service
0
500
1000
1500
2000
2500
3000
3500
Coa
ting
Tens
ile F
ailu
re L
oad,
psi
primer/substrate
within coating
glue
Negligible Flash Rust (Closed Loop)
Moderate Flash Rust (Hand Lance)
Tens
ile a
dhes
ion
abov
e 80
0 ps
i is
cons
ider
ed "g
ood"
per
form
ance
Light Flash Rust (Remediated Hand Lance)
Dominate Failure Location
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Inspecting Coating Over Flash Rust• Validate performance
by:– Adhesion Test (Pull-off or
knife cut)– Close inspection for
corrosion or blistering initiating at difficult to clean surfaces
– Chemically removing coating to observe substrate
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Key Concepts• SSPC SP-12 contains three important
criteria for a waterjet cleaned surface– Visible contaminants, Flash Rust & non-visible
contaminants• Current flash rust definitions are
subjective descriptions of color, appearance and adhesion– Several techniques are available which can
improve on the current definitions– Communication between contractor,
inspector, owner and coating supplier will facilitate consistent interpretation
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Key Concepts• Flash rust can be painted over
successfully– The allowable level depends on factors
such as the coating material and service environment
• Flash rust can adversely impact coating performance– Can cause poor adhesion or osmotic
blistering
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Questions?
Thank You For Attending!