Galvanizing Process Immersed in a bath of molten zinc ( F) > 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 (Hot-Dipped) 44' x 5'3" x 8'9" deep
Material Handling (racks or hooks)
Vent and Drainage
Material thickness Different thickness – –Reach bath temperature at different times – –Cools at different rate – –Maintaining original shape
Estimated Service Life of HDG
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
Hot-Dip Galvanizing Advantages Best protection Metallurgical bond Quality control Durable Interior (pipe/tubes) DisadvantagesVenting/drainage Size limits CrevicesDeformation Reduced slip coef. Field welds
2. Liquid Coatings Standard Specification 594 covers – –shop and field applications 1. 1."new steel" 2. 2."existing steel" (maintenance) 3. 3."rehabilitating coated steel" 4. 4."non-steel metallic" (galvanized, aluminum)
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 Scope
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?
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
Non-Steel Metallic Hot-dipped galvanizing – –surface prep per ASTM D Aluminum – –light brush blast or hand sand Shop or field application 2 coat system from QPL "Non-Ferrous Coating" - no zinc primer
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)
Liquid Coatings Advantages Any size/shape Shop or field Repairs match Lower initial cost DisadvantagesVOC's Quality control –contamination –film thickness –cure Shorter life
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
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
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
Blasted sign structure
Powder Coating Application Preheat surface Apply primer (within 4 hrs of cleaning) Heat to partially cure primer Apply topcoat Heat to finish cure
Application of Zinc Rich Primer
Powder Coatings Advantages No VOC's Quality Control Adhesion No dry spray Transport Damage Disadvantages Size limits Doesn't fill crevices Castings Field repairs
4. Duplex Systems Additional Coating over HDG Addressed in spec 593 and ASTM D Standard Practice for Preparation of Zinc (Hot-Dip) Galvanized Coated Iron & Steel Product & Hardware Surfaces for Painting Galvanizer & Painter must communicate
Duplex System vs HDG Advantages Service life Color choice Smooth finish Disadvantages Higher initial cost Quality control?
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
System Costs ($/SF)* HDGLiquid(new)Liquid(maint.)PowderDuplex 7-15** *** *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.
System Service Life (yrs)* CoatingEnvironHDGLiquid(new)Liquid(maint)PowderDuplex Marine W. Ore. (wet) E. Ore. (dry) *Approximate time until corrosion at defects affect structural integrity. Aesthetics may reduce life.