There are some very important factors to be considered at the design stage when a job is to be hot-dip galvanized. Factors such as venting and draining of hollow members, overall physical size, purpose-designed lifting points, steel composition and combinations of differing section sizes are critical to the ultimate success of the job.
The UnionGalv technical team is available to work with designers and fabricators and provide galvanizing advice in the design stage to ensure the highest quality finish, minimum costs and faster delivery. Below are the key things to consider in the design stage before galvanizing.
Materials
All ferrous materials can be galvanized. Mild and low alloy steels and iron and steel castings are successfully galvanized as are steel fabrications incorporating stainless steel parts and fittings.
Size and shape
Our large galvanizing baths and lifting equipment enable galvanizing of a wide variety of component shapes and sizes. Larger structures are galvanized by designing in modules or can be double-end dipped.
We recommend that you speak to our technical team about all large-structure galvanizing to ensure the design can be accommodated.
Venting, filling and draining
Hollow structures incorporating closed sections must have provision for venting during the galvanizing process for safety reasons.Correct venting also ensures the entire internal surface is properly galvanized.Tanks and closed vessels need to allow pickle acids, fluxes and molten zinc to enter, fill and flow upwards through an opening at the highest point, so air is not trapped in the vessel and to allow complete drainage of interior.
A filling hole as large as the design will allow should be provided opposite a vent hole of equal dimensions to allow air to escape and facilitate draining.
Distortion
Galvanizing is unlikely to cause distortion providing the design and fabrication recommendations are adhered to.
The galvanizing reaction between zinc and steel takes place in liquid zinc, at approximately 445-460 degrees Celsius. Steel invariably contains internal stresses and at this temperature hot-dip galvanizing can release or vary the stress so distortion is possible.
However, stresses in steel are more commonly caused during fabrication. Welding can result in extreme temperature differences within small areas resulting in residual stresses. To minimise the introduction of stresses during welding, components should not be forced, sprung or restrained during welding; different thicknesses of steel shouldn’t be jointed together; and welded assemblies should be aligned so that the stresses are balanced.
Large unsupported flat sheets may tend to buckle so stiffeners should be included in the design and frames around flat panels, whether solid or welded mesh should be galvanized separately.
Distortion can be minimised for fabricated products, such as girders or lattice beams with top or bottom chords of different size by rapid immersion in a single dip.
Weld areas
All welded sections of fabrication pipe work should be interconnected with open tee or mitre joints, or closed sections should be vented.
Fabricated columns and strengthening gussets fabricated from channel sections should have corners cropped to allow free flow of zinc during the galvanizing process.
Lifting points
The size, location and design of lifting points can be crucial in minimizing the possibility of distortion on heavy or complex structures.
Ensure lifting points are considered in the design stage. The UnionGalv technical services team can provide advice on the best location and strength of lifting points.