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Steel Coating Systems By: Ivan Silbernagel, P.E.

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Presentation on theme: "Steel Coating Systems By: Ivan Silbernagel, P.E."— Presentation transcript:

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 Galvanizing Valmont 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 Galvanizing Process 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)

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

8

9 Material Handling (racks or hooks)

10 Vent and Drainage ASTM A385 Standard Practice for "Providing High-Quality HDG Coatings" It addresses designing for HDG

11

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 Designer must specify what to paint
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 Scope

19 Existing Steel Spec 594 Designer must address 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 Aluminum
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)

23

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 Topcoat
zinc rich epoxy primer for steel epoxy primer for non-steel metallic Topcoat polyester meeting AAMA Spec 2605

27 Other non-steel metallic surfaces
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 Powder Coating Application
Preheat surface Apply primer (within 4 hrs of cleaning) Heat to partially cure primer Apply topcoat Heat to finish cure

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

33

34 4. Duplex Systems Additional Coating over HDG
Addressed in spec 593 and 594 ASTM D 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?

36

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 C Protecting Steel with Thermal Sprayed Coatings AWS C Thermal Spray Feedstock

38 System Costs ($/SF)* HDG Liquid (new) (maint.) Powder Duplex 7-15**
5-10 20-35*** +3-5 * 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)*
Coating Environ HDG Liquid (new) (maint) Powder Duplex Marine 25-40 15-25 10-20 40-60 W. Ore. (wet) 30-50 25-35 20-30 50-70 E. Ore. (dry) 75+ 35+ 30+ 50-100 *Approximate time until corrosion at defects affect structural integrity. Aesthetics may reduce life.


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