Applying Coatings over Flash Rust in a Marine Environment.

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 12Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating

Visible Contaminants

Visible Contaminants

Flash RustFlash Rust

Non-Visible Contaminants

Non-Visible Contaminants


• 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?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


Adhesion Tightly adherent Reasonably well adherent

Loosely adherent, easily comes off

Descriptors of Flash Rust in SSPC-SP 12/VIS-4
















What are the differences?

Descriptors of Flash Rust in SSPC-SP 12/VIS-4
















More distinct differences

Descriptors of Flash Rust in SSPC-SP 12
















Which metric takes precedence?

Which metric takes precedence?

Some distinctions less clear

Some distinctions less clear

Not QuantitativeNot Quantitative

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

Pe

rce

nta

ge

of

Re

sp

on

da

nts

Test Panel Number

None Light Moderate Heavy

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 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

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” TestModerate 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 tapesand 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

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40 45

Cat

ho

dic

Dis

bo

nd

men

t R

adiu

s -

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

Adhesion Data from Ships In Service

0

500

1000

1500

2000

2500

3000

3500

Co

ati

ng

Te

ns

ile

Fa

ilu

re L

oa

d,

ps

i

primer/substrate

within coating

glue

Negligible Flash Rust (Closed Loop)

Moderate Flash Rust (Hand Lance)

Te

ns

ile a

dh

esi

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ab

ove

80

0 p

si i

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co

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ide

red

"g

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nce

Light Flash Rust (Remediated Hand Lance)

Dominate Failure Location

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!

Applying Coatings over Flash Rust in a Marine Environment.

Documents

flash rust flash rust

flash rust slide

levels of flash rust

recoating flash rust

flash rust requirement

definitions flash rust

surface slide

uniform rust