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 Rust-back Rust bloom 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

Non-Visible Contaminants 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

Flash Rust – How do we describe this? 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 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 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 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 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 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 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 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 Adhesion Tightly adherent Reasonably well adherent Loosely adherent, easily comes off Not Quantitative Some distinctions less clear Which metric takes precedence?

How to Determine Level of Flash Rust NSRP Round Robin data

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 Lab testing suggests Moderate Flash Rust does not significantly impact cathodic disbondment of marine grade epoxies

Adhesion Data from Ships In Service

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

Thank You For Attending! Questions? Thank You For Attending!