Design characteristics

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DESIGNERS AND PRODUCERS HAVE TO KNOW THE PECULIARITIES OF THE PRODUCTS TO BE HOT-DIP GALVANIZED AND CONSULT WITH AS GALV-EST EXPERTS WHEN NEEDED.

Dimensions of the products:

The dimensions of the product to be hot-dip galvanized depend on the dimensions of the treatment baths and zinc baths used, and the Galv-Est plant gives the following recommended dimensions for the product or structure: 1,500 mm (width) x 2,700 mm (height) x 13,500 mm (length) and a max weight of 12 tonnes. Galvanizing of longer products is possible but in that case the plant has to be consulted extensively, and a double dipping of the product has to be considered necessary, which is not always permitted and includes additional costs.

Composite structures:

The best results are gained with a product that has been designed in such a way that the mass and axes of the geometric symmetry of the connected components coincide, since materials expand during the heating process and an uneven linear expansion may cause the product to warp. The use of materials of different thickness in the compound structures should also be avoided. If, for instance, intermittent welding is used to combine a massive profile that heats up slowly to a light profile material, then the latter one, which heats up faster, will warp due to linear expansion, which is usually permanent. Similarly, also, U-beams will warp during hot-dip galvanizing due to the faster heating of the sides of the box, but such deformations are relatively easily rectified.

It is also important that products made out on thin metal sheets are strengthened against deformation. In this case, better results are achieved with strengthening through bending; the use of profile steel support fins should be avoided.

Hollow structures:

When using hot-dip galvanizing it is important to know that the use of closed off profiles is very dangerous, since the closed in air usually causes the item to break open when it expands. It is also important that hollow products have openings for the draining of the liquid zinc in order to prevent waste and to keep the weight of the product from increasing too much. Without these openings galvanizing is not possible. Therefore products are designed with ventilation and drainage openings, which are based, above all, on the position in which the product is lowered into the bath.

If the design allows for it then the drainage openings should be as big as possible.

 

Examples for determining the locations of ventilation openings:

 

 

For each hollow structure, there has to be an opening in the highest and lowest part of the structure when being dipped; see the following illustration:

 

Table for draining and ventilation holes for different types of construction with hollow sections – recommended minimums:

Pipe diameter mm Pipe length and holes diameter mm
  3m 6m 9m 12m
20 10 ends open ends open ends open
30 12 ends open ends open ends open
40 14 20 ends open ends open
60 16 24 32 ends open
80 20 30 40 50
100 25 40 50 60
120 30 50 or 2 x 30 60 or 2 x 40 70 or 2 x 50
160 40 60 or 2 x 40 80 or 2 x 50 90 or 2 x 60
200 50 80 or 4 x 30 100 or 4 x 40 120 or 4 x 50
250 60 100 or 4 x 40 120 or 4 x 50 140 or 4 x 60
300 75 120 or 4 x 50 150 or 4 x 60 160 or 4 x 70

 
Containers and vessels:

Containers that have their inner surface hot-dip galvanized have to have openings that allow for the fast inflow, outflow, and complete emptying of the liquid zinc (for a closed reservoir of one square-metre there has to be an opening with a diameter of at least 40 mm).

 

The required sizes of the drainage openings depend on the volume of the container, as follows:

 

Volume
litres		 One drainage opening Ø mm Two drainage openings Ø mm Ventilation opening Ø mm
500 80   25
1000 115 2×80 40
1500 140 2×100 45
2000 160 2×115 55
2500 175 2×125 60
3000 200 2×140 70
3500 225 2×150 75
4000 225 2×160 80
4500 240 2×170 85
5000 250 2×175 90
5500 265 2×185 95
6000 280 2×200 100
7000 300 2×220 110
8000 325 2×225 115
9000 350 2×240 120
10000 350 2×250 125

 

Frequently Asked Questions

Bath sizes and recommended dimensions of components:

length 14.0 m- component 13.8 m
width 1.6 m- component 1.55 m
depth 3.0 m- component 2.8 m

  • Max lift weight – 8 tons

For any technical inquiries please contact the sales department.

Galvanizing time depends on the volume, size and type of the material. Generally, the galvanizing process lasts for about half a day, although one must consider the time of year as well as industry demand. Please contact us at the beginning of the design process, so we can give you advice on different construction and production methods. Many delays are caused by inadequate construction and the lack of knowledge concerning the galvanizing process. For further information please contact our sales department.

The international Galvanizers Association announced that today, a typical galvanized coating can reach a lifetime of up to 50 years in most environments, and up to 25 years in an urban/marine environment.

Dark or light grey – it is still galvanised.

Dark grey coatings provide the same protection as light grey coatings – and sometimes even better. If rimmed steel or killed steel with aluminium is hot-dip galvanized, layers of alloy are formed which are in turn covered in zinc with a blue-grey shine. On some occasions, zinc may form irregularly oriented crystals, creating an “opalescentâ€? effect, which is not an indication of good or bad hot-dip galvanizing, nor does opalescence affect the corrosion resistance of zinc coatings. During production, silicone is sometimes added to steel as a deoxidizing agent which accelerates the reaction between steel and molten zinc. If the steel component is removed from the galvanizing bath while it is still hot, the reaction may continue and transform the surface zinc layers (entirely or in part) into alloys of zinc and iron. Compared to the light grey colour of zinc, zinc-iron alloys have a darker grey colour and are more abrasion resistant. Normally, the coatings of zinc-iron alloys are thicker and therefore grant a longer lifetime than coatings of rimmed steel or killed steel with aluminium. In any case, zinc-iron alloys are at least as corrosion resistant as zinc; because of their thickness they may be more resistant to self-corrosion in acidic industrial environments. These thick coatings may be more sensitive to mechanical damage, especially when handled recklessly, so they must be handled with care. Spots of iron oxide may appear on surfaces with dark grey coating even in mild conditions if the surface is not completely dry. This is just a surface effect and does not develop into nodular or flaky rust: the galvanized coating is not broken and continues to protect the steel.

Flawlessly galvanized steel with a long corrosion-free life may sometimes reveal spots of rust or changes in colour. This may give a false impression of an unsuccessful coating and is visually unacceptable on some occasions. The main reasons for spots and colour changes are listed below with suggestions for avoiding further problems or dealing with a problem that has already occurred. Colour changes in galvanized coatings caused by rust may occur as a result of one or more of the following factors.

  • Direct contact between galvanized components and unprotected or insufficiently protected steel (e.g. slices of galvanized steel, secured with unprotected, galvanically covered or painted steel bolts).
  • Iron dust and iron residue on galvanized surfaces originating from other operations or sources.
  • Water runoff from unprotected or insufficiently protected steel constructions, e.g. unpainted areas of painted steel constructions.
  • During the etching process, hydrochloric acid may penetrate the weld area due to pinholes or intermittent welds. Water may sometimes accumulate in residual salts, causing “leakingâ€? in weld areas. This effect is usually limited to a small area, stops after a short while and does not damage the coating.
  • Rusting of areas that have been welded after galvanizing and left uncovered or covered insufficiently.
  • Spots may appear on galvanized material if water is running off of other materials, metals such as copper and certain hardwoods such as oak in particular; in fact, every time water can dissolve material from a surface and precipitate them to galvanized steel.

Avoidance

If possible, all components of the constructions should receive equal corrosion protection. The thinner zinc coatings used in steel mesh, sheets, wire and pipes do not often last as long as the coatings of hot-dip galvanized components that have been galvanized in accordance with the BS/IS EN ISO 1461 standard which concerns all constructions that have been galvanized after production. If possible, the welding should be continuous and slag-free in order to minimize the preservation of etching residues. Design the constructions so that water cannot run off of other materials onto galvanized steel. Runoff from insufficiently protected steel and copper should certainly be avoided. If welding is required after galvanization, the welded areas should be cleaned thoroughly and the zinc coating should be restored with zinc dust paint or repair mastics sold by the brand, in accordance with the BS/IS EN ISO 1461 §6.3 standard. Corrective changes Colour changes and spots do not affect the lifetime of the coating. However, you can clean the corresponding areas to improve the appearance of the construction. Generally, using a steel brush or scouring powder will remove the spot and leave a flawless galvanized coating.

Small galvanized areas may be damaged by operations such as cutting or welding performed after galvanizing. Because of the protector in zinc, small local defects (up to 5 mm in diameter) tend to be fixed on their own and do not significantly affect the lifetime of surfaces. Nonetheless, it is recommended to renew the coating for aesthetic purposes on both smaller and larger surfaces, using one of the following techniques.

  • Brush the surfaces thoroughly with a steel brush and apply several layers of zinc dust paint to form a coating at least as thick as the initial galvanized coating.
  • Brush the surfaces thoroughly with a steel brush, heat the bare surface area to 300 °C with a blowtorch and apply a specific soldering rod with alloy of zinc. Applying zinc dust paint is usually the easiest option, but if colour matching is important, the zinc alloy soldering rods are more suitable.

For any technical inquiries, please contact the sales department.

If the client brings constructions with hidden holes and claims that all nessesary holes are made according to the instructions then they must send confirmation letter or on site write a letter to our stockkeeper what confirms that information. If we have an accident in the production because of the missing holes then this company is financially responsible.