Applying Coatings over Flash Rust in a Marine Environment

1. Applying Coatings over Flash Rust in a Marine Environment

2. 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.

3. 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

4. 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

5. Robotic Equipment Incorporates water removal devices Little to no flash rust

6. 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

7. SSPC-SP 12Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating Visible Contaminants Non-Visible Contaminants Flash Rust

8. 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)

9. 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

10. Inspecting Flash Rusted Surfaces

11. SSPC-SP 12Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating Flash Rust – How do we describe this?

12. 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.

13. Descriptors of Flash Rust- SSPC SP-12/VIS-4

14. Descriptors of Flash Rust in SSPC-SP 12/VIS-4 What are the differences?

15. Descriptors of Flash Rust in SSPC-SP 12/VIS-4 More distinct differences

16. Descriptors of Flash Rust in SSPC-SP 12 Not Quantitative Some distinctions less clear Which metric takes precedence?

17. How to Determine Level of Flash Rust • NSRP Round Robin data

18. 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)

19. 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

20. Suggested “Brush-Cloth” Wiping Test Recommended to improve consistency of evaluation

21. Suggested “Brush-Cloth” Wiping Test

22. Removal of Flash Rust by Pressure Washing

23. Hempel “Ten Tape” Test Moderate Heavy

24. 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

26. Works with different tapesand meters

27. “Light” (1-8% Change in Transmittance)

28. “Moderate” (10-20% Change in Transmittance)

29. “Moderate-Heavy” (14-24% Change in Transmittance)

30. “Heavy” (21-50% Change in Transmittance)

31. Applying Coatings Over Flash Rust

32. 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

33. 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)

34. 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”)

35. Laboratory Data • Lab testing suggests Moderate Flash Rust does not significantly impact cathodic disbondment of marine grade epoxies

36. Adhesion Data from Ships In Service

37. 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

38. 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

39. 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

40. Questions? Thank You For Attending!