Steel Coating Systems

1. Steel Coating Systems By: Ivan Silbernagel, P.E. Structure Coatings Engineer ODOT Construction Section

2. Coating Options • Hot-Dip Galvanizing (spec 2530) • Liquid Coatings (spec 594) • Powder Coatings (spec 593) • Duplex Systems (spec 593 & 594) • Thermal Spray Coatings (AWS)

3. 1. Hot-Dipped GalvanizingValmont Coatings Pacific States Galvanizing

4. HDG Surface Prep Steps • Degreasing - Removes dirt, oils, organic residue • Sulfuric Acid Pickling - Removes mill scale and oxides • Fluxing - Mild cleaning, provides protective layer

5. Sulfuric Acid Pickling

6. Immersed in a bath of molten zinc (≈ 830 0F) > 98% pure zinc, minor elements added for coating properties (Al, Bi, Ni) Removed after reaching bath temperature (approx 5 to 7 minutes) Zinc reacts with iron in the steel to form galvanized coating Creates 4 layers (3 zinc alloys w/ zinc topcoat) Galvanizing Process

7. Galvanizing (Hot-Dipped)44' x 5'3" x 8'9" deep

9. Material Handling (racks or hooks)

10. Vent and Drainage

12. Oversize dipping

13. Material thickness • Different thickness • Reach bath temperature at different times • Cools at different rate • Maintaining original shape

14. Estimated Service Life of HDG

15. ASTM Standards for Galvanizing • Galvanized Products • ASTM A 123 – general • ASTM A 153 – small parts (fasteners) • ASTM A 767 – rebar • Supporting Specifications • ASTM A 143 – embrittlement • ASTM A 384 – distortion • ASTM A 385 – high-quality coatings • ASTM A 780 – repair • ASTM D 6386 – surface prep for painting over

16. Hot-Dip Galvanizing Advantages • Best protection • Metallurgical bond • Quality control • Durable • Interior (pipe/tubes) Disadvantages • Venting/drainage • Size limits • Crevices • Deformation • Reduced slip coef. • Field welds

17. 2. Liquid Coatings • Standard Specification 594 covers • shop and field applications • "new steel" • "existing steel" (maintenance) • "rehabilitating coated steel" • "non-steel metallic" (galvanized, aluminum)

18. New Steel • Spec 594 • Near white blast • Shop application • 3 coat system from QPL • "Shop Coating" - primer is inorganic • or "Shop & Maintenance Coating" - organic primer • No separate measurement or pay • Designer must specify what to paint • General note and/or modify 594.00 Scope

19. Existing Steel • Spec 594 • Near white blast • Mostly field applications • 3 coat system from QPL • "Shop & Maintenance Coating" • Designer must address • What to and not to paint (inaccessible areas?) • Do you want a warranty?

20. Rehabilitating Steel (Removal or installation of components) • Spec 594 • Commercial Grade Power Tool Cleaning • Field applications • 3 coat system from QPL • "Rehab Coating" - surface tolerant zinc primer • Designer must specify • What to and not to paint

21. Non-Steel Metallic • Hot-dipped galvanizing • surface prep per ASTM D6386 • Aluminum • light brush blast or hand sand • Shop or field application • 2 coat system from QPL • "Non-Ferrous Coating" - no zinc primer

22. Liquid Coatings • Specification 594 does not cover: • 1 and 2 coat systems • overcoat systems • special uses (i.e. submerged, cables, anti-skid, etc.) • special colors (Federal Color Standard 595B) • non-visible contaminates (salts)

24. Liquid Coatings Advantages • Any size/shape • Shop or field • Repairs match • Lower initial cost Disadvantages • VOC's • Quality control • contamination • film thickness • cure • Shorter life

25. 3. Powder Coatings • Specification 593 covers applications on new and existing structures • used for small to medium sized parts (railing, sign structures, light poles, etc.) • PTI size limited to 52' x 14' x 12' high

26. Powder Coatings • spec 593 requires a 2 coat system • Primer • zinc rich epoxy primer for steel • epoxy primer for non-steel metallic • Topcoat • polyester meeting AAMA Spec 2605

27. Surface Prep Steps • Steel surfaces • "Near White" abrasive blast • Phosphate treat immediately and dry with heat • Galvanized surfaces • ASTM D6386 • Other non-steel metallic surfaces • Light abrasive blast or hand sand

28. Blasted sign structure

29. Phosphate treatment

30. Preheat surface Apply primer (within 4 hrs of cleaning) Heat to partially cure primer Apply topcoat Heat to finish cure Powder Coating Application

31. Application of Zinc Rich Primer

32. Powder Coatings Advantages • No VOC's • Quality Control • Adhesion • No dry spray • Transport Damage Disadvantages • Size limits • Doesn't fill crevices • Castings • Field repairs

34. 4. Duplex Systems • Additional Coating over HDG • Addressed in spec 593 and 594 • ASTM D 6386 - Standard Practice for Preparation of Zinc (Hot-Dip) Galvanized Coated Iron & Steel Product & Hardware Surfaces for Painting • Galvanizer & Painter must communicate

35. Duplex System vs HDG Advantages • Service life • Color choice • Smooth finish Disadvantages • Higher initial cost • Quality control?

37. 5. Thermal Spray Coating • No ODOT Standard Spec • Can be done in shop or field • Surface cleanliness critical • Seal with a topcoat for better performance • AWS C2.18 - Protecting Steel with Thermal Sprayed Coatings • AWS C2.25 - Thermal Spray Feedstock

38. System Costs ($/SF)* * Approximate cost, includes prep and application. Size, shape, and quantity affect costs. ** May require more SF than other systems. Use 0.45 to 0.60 $/lb. for estimating cost ***Includes full removal and recoating. 60 to 80% of cost is for containment and surface prep.

39. System Service Life (yrs)* *Approximate time until corrosion at defects affect structural integrity. Aesthetics may reduce life.