Transcript Structural Designs that Accelerate Corrosion

Applying Coatings over Flash
Rust in a Marine Environment
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.
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
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
Robotic Equipment
• Incorporates water removal devices
• Little to no flash rust
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
SSPC-SP 12
Surface Preparation and Cleaning of Metals by Waterjetting Prior to
Recoating
Visible Contaminants
Non-Visible
Contaminants
Flash Rust
SSPC-SP 12
Surface 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)
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
Inspecting Flash Rusted
Surfaces
SSPC-SP 12
Surface Preparation and Cleaning of Metals by
Waterjetting Prior to Recoating
Flash Rust – How do we describe this?
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.
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
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 Obscures the original
observed
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?
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
Descriptors of Flash Rust in SSPC-SP 12
Metric
Light
Moderate
Heavy
Color
Yellow-brown
Yellow-brown
Red-brown
Obscures the original
steel surface
Hides the initial surface
condition completely
Leaves light marks
Leaves significant marks
Substrate
Steel substrate may be
Not Quantitative
observed
“Lightly wiping”
with a cloth
Not easily removed
distinctions
less aclear
SmallSome
quantities
of
Exhibits
layer
a…rust layer
of…rust
Exhibits a layer of
heavy…rust
Distribution
Evenly distributed or
present in patches
Evenly distributed or
present in patches
Adhesion
Tightly adherent
Volume
Evenly distributed or
present in patches
Which
metric
Reasonably
well takes precedence?
Loosely adherent, easily
adherent
comes off
How to Determine Level of Flash Rust
• NSRP Round Robin data
100%
None
Light
3
4
Moderate
Heavy
90%
80%
Percentage of Respondants
70%
60%
50%
40%
30%
20%
10%
0%
8
6
7
Test Panel Number
1
2
5
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)
Recommended Guidelines for
Evaluating 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
Suggested “Brush-Cloth” Wiping
Test
• Recommended to improve consistency of
evaluation
Suggested “Brush-Cloth” Wiping
Test
Removal of Flash Rust by
Pressure Washing
Hempel “Ten Tape” Test
Moderate
Heavy
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
Works with different tapes
and meters
“Light”
(1-8% Change in Transmittance)
“Moderate”
(10-20% Change in Transmittance)
“Moderate-Heavy”
(14-24% Change in Transmittance)
“Heavy”
(21-50% Change in Transmittance)
Applying Coatings Over Flash
Rust
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
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)
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”)
Laboratory Data
Cathodic Disbondment Radius - mm
• Lab testing suggests Moderate Flash Rust does
not significantly impact cathodic disbondment of
marine grade epoxies
50
45
40
35
30
25
20
15
10
5
0
0
5
SP-10/SP-7
10
15
Light20FR
25 Moderate
30 FR 35
Heavy
40 FR 45
Adhesion Data from Ships In
Service
3500
2500
2000
1500
primer/substrate
Tensile adhesion above 800 psi is
considered "good" performance
Coating Tensile Failure Load, psi
3000
Dominate Failure Location
within coating
glue
1000
500
0
Negligible Flash Rust
(Closed Loop)
Moderate Flash Rust
(Hand Lance)
Light Flash Rust
(Remediated Hand Lance)
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
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
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
Questions?
Thank You For Attending!