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
Non-Visible Contaminants
Flash Rust
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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 arust layer Exhibits a layer ofrust Exhibits a layer of heavyrust
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 arust layer Exhibits a layer ofrust Exhibits a layer of heavyrust
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 arust layer Exhibits a layer ofrust Exhibits a layer of heavyrust
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 arust layer Exhibits a layer ofrust Exhibits a layer of heavyrust
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
Not Quantitative
Some distinctions less clear
Which metric takes precedence?
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How to Determine Level of Flash Rust

• NSRP Round Robin data

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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 Test
Moderate
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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(No Transcript)
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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

• 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
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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!