Design for Galvanizing Designing for hot-dip galvanizing

Products that follow the essential design and fabrication requirements will ensure high quality galvanized products, minimum cost and faster delivery. Adopting the proper design practices will ensure the safety of galvanizing personnel, reduce coating cost, and produce optimum quality galvanizing.

Below is the list of some of the basic rules which should be used in design and fabrication:

  • Follow the design guidance about vent holes in hollow sections
  • Provide an additional clearance equal to 4x the coating thickness on threaded fasteners
  • A 1mm extra clearance on all matting surfaces is required
  • Low melting point soldered joints can NOT be galvanized as they will collapsed during the process
  • Anti splatter paints containing silicon should NOT be used
  • Please remove moulding sand from castings by grit blasting
  • Avoid overlapping surfaces if possible. If you cannot avoid them, make sure you follow the venting guidance

Basic Venting and Draining Guideines

  1. No vent hole should be less than 10mm in diameter unless otherwise agreed with the galvanizer
  2. Preferred minimum vent hole size is 12mm
  3. Vent holes should not be located in the centre of end plates and connections
  4. Vent holes should be located at the edges of hollow sections oriented in the same plane as the fabrication
  5. Large hollow vessels require 1250mm² of vent hole area for each cubic metre of enclosed volume. This is equivalent to a 40mm diameter hole for every cubic metre of volume
  6. Hollow sections (pipe, RHS, and SHS) ideally require vent holes equivalent to 25‰ of the sections' cross section, made up of single or multiple vent holes. The preferred design option is to leave the ends of hollow sections completely open
  7. Hollow sections that are connected require external vent holes as close to the connection as possible. If internal vent holes are used, they should be a total of at least 50‰ of the internal diameter of the connecting section
  8. Large seal welded overlapping surfaces will require venting if the enclosed area may contain condensation or allow process chemicals to enter the overlap during the galvanizing process. Overlaps between 10,000mm² and 40,000mm² should be vented with a 10mm vent hole. Overlaps under 10,000mm² generally do not require venting. Intermediate sized overlaps should be judged on the basis of weld integrity and residual welding heat in the joint to ensure total dryness at time of sealing. Longer or larger overlapping areas require spaced holes for progressive venting. Very large overlapping areas should be avoided as an undesirable design for galvanizing or corrosion protection in general
  9. Vent and drain holes must be located as close to the high and low points of the hollow section as possible to prevent air locks, entrapment of pre-treatment chemicals and zinc puddling
  10. No drain hole should be less than 10mm
  11. Preferred minimum drain hole size is 25mm particularly for items with a large internal volume
  12. Large hollow sections (tanks, pressure vessels) require a 10,000mm² diameter of drain hole area for each cubic metre of enclosed volume
  13. Drain holes should be at the edges of hollow sections
  14. Hollow sections such as tube, RHS and SHS require minimum drain hole area equivalent to 25‰ of the sections' diagonal cross section. The preferred design option is to leave the ends of tubes, RHS and SHS open

Source: Galvanizers Association of Australia

Jl. Jababeka XII B Kav. V No. 38 - Cikarang-Bekasi