12. Illustrated Guide to Designing for Galvanizing

  1. Hot Dip Galvanizing
  2. Centrifuge processing of small partsg
  3. End plate design
  4. The Sandelin Diagram
  5. Welding and weld metal
  6. Zinc drainage off large items
  7. Orientation and surface fi nish
  8. Venting and draining of structural sections
  9. Design detailing
  10. Design details for angle fabrications
  11. Detailing complex fabrications
  12. Zinc buildup and clearances
  13. Draining larger hollow sections
  14. Pipe spools and other 2-D and 3-D hollow section fabrications
  15. Venting and draining of handrails
  16. Vent and drain hole size
  17. Back-to-back sections
  18. Minimising distortion in thin sections
  19. Design for fence panels and balustrade



1. Hot Dip Galvanizing:

The price is quoted on a $/kg basis for smaller projects or a $/tonne basis on larger tonnages. These costs will be highly variable and will be determined by the ease of handling through the galvanizing process, and the mass that can be processed in a given time, along with the zinc pickup on the item.

2. Centrifuge processing of small parts:

Hot dip galvanizing of small parts is done using the centrifuge process, where the pre-treated parts are galvanized in baskets that are spun at high revolutions after withdrawal from the molten zinc to remove excess zinc from their surfaces.

  • 3. End plate design:

    Base plates and end plates need to be designed for adequate venting and draining. Simple detailing during fabrication, as shown here, will produce good galvanizing results.

  • 4. The Sandelin Diagram:

    Steel chemistry determines the rate at which the steel will react with the molten zinc alloy in the galvanizing bath to form the galvanized coating. Silicon is the most signifi cant reactive alloying element in structural steels. This graph shows the reaction rate of steel with zinc at various steel silicon levels, and will give an indication of the likely galvanized coating characteristics of a steel of known silicon composition.

  • 5. Welding and Weld Metal:

    Weld metal composition and welding techniques can affect the fi nished appearance of fabrications. Weld metal is normally high in silicon content and will react with the molten zinc alloy at a higher rate that the parent metal. Weld areas ground fl ush prior to galvanizing may thus appear raised above the metal surface after galvanizing. Weld splatter will not be removed in the pre-treatment process and will be galvanized on the surface, creating an unsightly appearance.

  • 6. Zinc drainage off large items:

    The angle with which large fabrications can be withdrawn from the bath will determine the effectiveness of the drainage of excess zinc from its surfaces.

  • 7. Orientation and surface finish:

    The steeper the angle at which a fabrication can be withdrawn from the galvanizing bath, the smoother the fi nish is likely to be. The fl atter the surface is with respect to the molten zinc, the more drips, drainage spikes and feathers will occur on the edges. Provision of lifting points to allow the optimum orientation will produce the most consistent surface fi nish.

  • 8. Venting and draining of structural sections:

    Beams, columns and channels that contain gussets, splice plates or stiffeners in their design will not galvanize satisfactorily unless both zinc and air can get free access to all surfaces of the sections. Cropping of gussets and stiffeners fabricated into these sections will ensure a good galvanizing outcome.

  • 9. Design detailing:

    Simple detailing will ensure that adequate venting and draining of fabricated assemblies will deliver a good quality hot dip galvanized fi nish.

  • 10. Design details for Angle Fabrications:

    1-, 2-, or 3- dimensional angle fabrications need to be designed to consider their venting and draining characteristics during hot dip galvanizing. Using outward facing angles, rather than conventional inward-facing angles, in 3-D fabrications can eliminate the need for any special venting or draining requirements.

  • 11. Detailing complex Fabrications:

    For complex fabrications, advice should be sought from the galvanized to ensure that adequate lifting points, and venting and draining requirements are incorporated into the fabrication.

  • 12. Zinc buildup and clearances:

    The surface tension and fl uidity of molten zinc will result in thickening of the galvanized coating at low points on solid and hollow circular sections. Where clearances for the fi tting of mating parts is requires, this thickness variation needs to be accommodated in the design, particularly on internal surfaces of hollow sections where removal of excess zinc is diffi cult.

  • 13. Draining larger hollow sections:

    Larger hollow sections used for structural applications have a signifi cant internal volume so venting and draining of base plates and end plates needs to accommodate the fl ow of larger volumes of pre-treatment chemicals and molten zinc. The location of drain holes in base plates and end plates will be determined by the orientation of the section during galvanizing.

  • 14. Pipe spools and other 2-D and 3-D hollow section fabrications:

    require careful detailing to ensure safe and satisfactory galvanizing. Moisture trapped inside the fabrication is an explosion hazard, and air trapped inside will prevent the item from sinking into the molten zinc.

  • 15. Venting and draining of handrails:

    Stanchions and handrails fabricated from hollow sections need to be vented and drained on the underside or inside to prevent ingress of rainwater and hazards to the pedestrians using the handrails.

  • 16. Vent and drain hole size:

    Vent and drain holes that are too small in hollow sections increase immersion time and may cause unsightly excessive zinc drainage runs as the zinc freezes during the draining period.

  • 17. Back-to-back sections:

    Where back-to-back angle or channel fabrications need to be hot dip galvanized, welding to create large overlapping surface areas should be avoided. The use of packers between the sections, or using channels toe-to-toe will ensure a good galvanizing outcome.

  • 18. Back-to-back sections:

    Where back-to-back angle or channel fabrications need to be hot dip galvanized, welding to create large overlapping surface areas should be avoided. The use of packers between the sections, or using channels toe-to-toe will ensure a good galvanizing outcome.

19. Design for fence panels and balustrade

Where hollow sections are used in the fabrication of fence panels and balustrades to be hot dip galvanized, the pre-treatment chemicals and molten zinc must be able to fl ow freely into and out of the fabrication. Venting and draining on the underside of fence panels and balustrade will not effect their appearance and will not allow weather to enter the panels.