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 coatingCreates 4 layers (3 zinc alloys w/ zinc topcoat)
15 ASTM Standards for Galvanizing Galvanized ProductsASTM A 123 – generalASTM A 153 – small parts (fasteners)ASTM A 767 – rebarSupporting SpecificationsASTM A 143 – embrittlementASTM A 384 – distortionASTM A 385 – high-quality coatingsASTM A 780 – repairASTM D 6386 – surface prep for painting over
16 Hot-Dip Galvanizing Advantages Best protection Metallurgical bond Quality controlDurableInterior (pipe/tubes)DisadvantagesVenting/drainageSize limitsCrevicesDeformationReduced 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 blastShop application3 coat system from QPL"Shop Coating" - primer is inorganicor "Shop & Maintenance Coating" - organic primerNo separate measurement or payDesigner must specify what to paintGeneral note and/or modify Scope
19 Existing Steel Spec 594 Designer must address Near white blast Mostly field applications3 coat system from QPL"Shop & Maintenance Coating"Designer must addressWhat to and not to paint (inaccessible areas?)Do you want a warranty?
20 Rehabilitating Steel (Removal or installation of components) Spec 594Commercial Grade Power Tool CleaningField applications3 coat system from QPL"Rehab Coating" - surface tolerant zinc primerDesigner must specifyWhat to and not to paint
21 Non-Steel Metallic Hot-dipped galvanizing Aluminum surface prep per ASTM D6386Aluminumlight brush blast or hand sandShop or field application2 coat system from QPL"Non-Ferrous Coating" - no zinc primer
22 Liquid Coatings Specification 594 does not cover: 1 and 2 coat systems overcoat systemsspecial 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 costDisadvantagesVOC'sQuality controlcontaminationfilm thicknesscureShorter life
25 3. Powder CoatingsSpecification 593 covers applications on new and existing structuresused 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 steelepoxy primer for non-steel metallicTopcoatpolyester meeting AAMA Spec 2605
27 Other non-steel metallic surfaces Surface Prep StepsSteel surfaces"Near White" abrasive blastPhosphate treat immediately and dry with heatGalvanized surfacesASTM D6386Other non-steel metallic surfacesLight abrasive blast or hand sand
34 4. Duplex Systems Additional Coating over HDG Addressed in spec 593 and 594ASTM D Standard Practice for Preparation of Zinc (Hot-Dip) Galvanized Coated Iron & Steel Product & Hardware Surfaces for PaintingGalvanizer & Painter must communicate
35 Duplex System vs HDG Advantages Service life Color choice Smooth finishDisadvantagesHigher initial costQuality control?
37 5. Thermal Spray Coating No ODOT Standard Spec Can be done in shop or fieldSurface cleanliness criticalSeal with a topcoat for better performanceAWS C Protecting Steel with Thermal Sprayed CoatingsAWS C Thermal Spray Feedstock
38 System Costs ($/SF)* HDG Liquid (new) (maint.) Powder Duplex 7-15** 5-1020-35***+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)* CoatingEnvironHDGLiquid(new)(maint)PowderDuplexMarine25-4015-2510-2040-60W. Ore.(wet)30-5025-3520-3050-70E. Ore.(dry)75+35+30+50-100*Approximate time until corrosion at defects affect structural integrity. Aesthetics may reduce life.