Certain rules must be followed when designing components for galvanizing, but the rules are readily applied and in many cases they are simply those which are good practice to ensure maximum corrosion protection. Adoption of the following design practices will ensure the safety of galvanizing personnel, ease the galvanizer's task, and produce optimum quality galvanizing. If in doubt concerning preferred design details check with galvanizer.
Filling, venting and drainage    

Good design requires:
- means for the access and drainage of molten zinc
- means for escape of gases from internal compartments (venting)
It is important to bear in mind that the steelwork is immersed into and withdrawn from a bath of molten zinc at about 450ûc. Thus any features which aid the access and drainage of molten zinc will improve the quality of the coating and reduce costs.

With certain fabrications, holes which are present for other purposes may fulfil the requirements for venting and draining; in other cases it may be necessary to provide extra holes for this purpose.

For complete protection, molten zinc must be able to flow freely to all surfaces of a fabrication. With hollow sections or where there are internal compartments, the galvanizing of the internal surfaces eliminates any danger of hidden corrosion during service.

General principles
1. Holes for venting and draining should be as large as possible. The minimum hole diameters are given in Table 6.
2. Holes for venting and draining should be diagonally opposite to one another at the high point and low point of the fabrication as it is suspended for galvanizing.
3.With hollow sections sealed at the ends, holes should be provided, again diagonally opposite one another, as near as possible to the ends. In some cases it may be more economical to provide V or U shaped notches in the ends, or to grind corners off rectangular hollow sections - these procedures provide ideal locations for venting and draining.
4.Internal and external stiffeners, baffles, diaphragms, gussets etc., should have the corners cropped to aid the flow of molten zinc.

Holes that have been drilled for venting can be plugged, but this is mainly necessary for aesthetic reasons, because a galvanized coating covers all surfaces. If required, tapered aluminium or plastic plugs are available and will prevent undesirable ingress of water. Detailed design advice is available from Galvanizers Association or directly from the galvanizer. Some points to bear in mind for venting and draining are illustrated in the diagrams on is pages

Base metal and combinations
Plain carbon steel, some low-alloy steels and iron and steelcastings can all be galvanized.

A fabrication consisting of a variety of materials with different surface conditions should be avoided as this could affect the uniformity and appearance of the coating. Where differing materials are used, grit blasting the entire assembly can minimise any differences which may arise due to differing effects of pretreatment. Preferably, the fabrication should be of similiar steel type throughout.
Size and shape
When the length, width or depth of the item exceeds the size of the bath, special techniques may be employed to facilitate dipping. The galvanizer should be consulted. (Measurement of Galvanizing Bath)
Overlapping surfaces
Overlapping surface should be avoided as far as possible. Care must be taken not to specify sealed articles for galvanizing. If overlaps are completely sealed by welding there is a risk of explosion during dipping due to increase pressure of any entrapped air. If overlaps are not completely sealed there is a danger of cleaning fluid entering the cavity and then weeping out and causing localised staining.
Casting
Castings must be grit blasted before galvanizing as embedded sand from the casting process cannot be removed by conventional chemical cleaning. When designing castings to be galvanized, features such as sharp corners and deep recesses should be avoided as these may develop excessive distortion and thermal stresses during hot dip galvanizing.
Moveable parts
Drop handles, hinges, shackles, shafts, and spindles require provision of minimum radial clearances as detailed in the table below, to allow for the thickness of the galvanized coating.
Shaft or spindle size
Up to 10mm diameter
10 to 30mm diameter
Over 30mm diameter		 Minimum radical clearance
1mm
2mm
2.0 to 2.5mm 		 
Distorion
Distortion can be prevented or minimised by :
1. Use of symmetrical designs.
2. Use of relatively uniform sections.
3. Use of accurately preformed members to avoid locked-in stresses.
4. Use of balanced or staggered welding techniques to avoid locked - in stresses.
5. Large open fabrications and tanks may require temporary cross stays to prevent distortion during galvanizing.
Strength
The tensile properties of structural steels are not affected by galvanizing, as shown in Table 7.
Welding
Welding slag is not removed in the cleaning process and may result in black bare spots after hot dip galvanizing. To avoid this problem, efforts should be made to use gas shielded welding processes e.g. M.I.G. and if coated electrodes are used, welds should be thoroughly de-slagged. In order to minimise the incidence of raised weld seams after hot dip galvanizing the silicon content of the welding rod material should be less than 0.04%.
Labelling and marking
Water soluble paint or detachable metal labels can be used for temporary identification marks on fabrications. Enamel based paints or oil based markers must not be used. For permanent identification, to be legible after galvanizing, large heavily punched or embossed marks are necessary.
Masking
If certain areas of steelwork need to remain uncoated this can be achieved by masking, using high temperature tape, chemical resistent paint (e.g.epoxy). Again, the galvanizer should be consulted about any areas required to be masked.
Handing of articles
Depending upon size and shape, articles for galvanizing may require suspension holes or lifting lugs. They may alternatively be handled by chains or, for smaller articles, on racks or in baskets. In the case of tanks (in particular, open tanks), cross stays may be necessary to ensure the shape of the vessel is maintained during handling.

Surface contamination
Clean steel surfaces are an essential requirement for good hot dip galvanizing. Contamination in the form of grease, tar paint and weld slag cannot be removed by chemical cleaning and may result in black bare spots after hot dip galvanizing. Fabricator should takes responsibility to ensure that articles being delivered free from contamination. (otherwise, an additional charge for shot-blasting may be added)

Anti-spatter weld sprays should be water-soluble to allow removal by the galvanizer during the pretreatment stages.
 
External stiffener, welder gussets and webs on columns and beams, and gussets in channel sections should have their corners cropped. Cropping the corners can prevent the entrapment of air in pockets and corners allowing complete access of pickle acids and molten zinc to entire surface of the work, also will aid access and drainage of molten zinc, thus a cleaner coating will be obtained.
Angle bracings should, if possible, be stopped short of the main boom flange.
On structural hollow sections, provision must be made for venting and draining. With vertical members, drilled holes or V notches should be provided diagonally opposite each other at top and bottom.
 
Every sealed section of a fabrication must be vented for reasons of safety and to allow access and drainage of molten zinc. Holes diagonally opposite each other should be as close as possible to the sealed end.  
 
If contacting surfaces cannot be avoided, as with these channels, then the edges of the contacting areas should be continuously welded and a hole drilled through both members to eliminate the danger of an explosion in the galvanizing bath. If this is not possible then welding should be intermittent: in service there may be some weeping rust stains from acid residues trapped between the plates but this will not be detrimental to the protection given by the coating. It will not generally be necessary to make any provision if the enclosed area is less than about 70cm.  
Internal diaphragms in large box sections should have croopped corner and a ÔmanholeÕ. Internal diaphragms on small box sections should have cropped corners. Where any hollow section is vented internally it is essential, for safety reasons, that the galvanizer is able to view such venting.  
External stiffeners for beams or channels should have the corners cropped.  
Alternative designs for venting sections fixed to base plates.  
Internal threads and nuts must be tapped oversize after galvanizing to accommodate the thickness of the galvanized coating on the stud or bolt.  
Welded joints should be continuous if they are not enclosing an otherwise unvented surface. Bolted joints are best made after galvanizing.  
To minimise the risk of distortion, flat panels should be braced. Openings should be provided in the corners.  
Large open top tanks should be stayed to minimise distortion. Where angles are used to rim the tank, appertures must be provided in the comers. Angles or flats used as stays should be as close as possible to the tank wall thickness.  
Vents should be diametrically opposite and at least 50mm in diameter. Internal Baffles should be cropped top and bottom. Lifting lugs are required as indicated. It should be possible to view the baffle through either the vent holes or an inspection hole - the placement of the inspection hole should be discussed with the galvanizer.