We are one of the largest hot dip galvanizers in Europe

With over 63 years of experience and 4 plants located in Spain and Portugal, Industrias Duero is one of the largest galvanizers in Europe.

  • We provide quality galvanizing
  • We can galvanize under any International standard EN ISO 1461, BSI, AASTHO…..whether hot-dip or centrifugal galvanizing.

We have furnaces up to 14 (L) x 2.2 (W) x 3 (H) m.

In Europe, hot dip galvanizing coatings on iron and steel articles are regulated by standard EN ISO 1461. However, under customer request, we can also galvanize under AASTHO specifications, or any other standard that is required.

Pre-galvanizing recommendations, in order to obtain a good final product

When buying iron or steel to be galvanized, make sure you inform your supplier that the material must be appropriate for galvanizing, as not all steel qualities are suitable for this purpose.

If the iron or steel are not suitable for galvanizing, it often leads to reactivity problems (high concentrations of silicon and phosphorus in the chemical composition, causing the Zn to laminate in layers, or even wash away due to the absence of a proper zinc-steel alloy).

Colours on the finished part may also appear dull and faded which, although it does not alter the corrosion resistance of the coating, it worsens the appearance of the products and increases the total cost for the customer, as the absorbed Zinc layer tends to become thicker.

Steel grade
Silicon + Phosphorous %
Type of coating
Si + P < 0,03 %
Standard Zinc-iron alloy Bright silver, standard thickness coating
0,03%< Si + P < 0,13 %
Sandelin finishing: High Zinc-iron reactivity Dark grey, thick coating
0,13 %< Si + P < 0,28 %
Sebisty finishing: Standard zinc-iron coating Silver matte finishing
Si + P > 0,28 %
High Zinc-iron reactivity Dark grey, thick coating
The quality of the steel used in the parts to be galvanized, can be laboratory tested in a direct and simple way, by analysing a sample material in a tube-test with a mass spectrometer. In order to avoid costly and unpleasant surprises in your projects, be sure to verify your steel fabrications are suitable for galvanizing.
While the above principles are valid for any steel type, when it comes to laser cut parts, customers must take into consideration that laser-cutting may produce sharp edges and burrs which are difficult to remove in the galvanizing process. Therefore it is highly advisable to use Nitrogen (not Oxygen) for laser-cutting or, else, remove any sharp edges/burrs once the part has been cut.
The temperature of the zinc-bath during the galvanizing process is 450º. When immersing metal parts in the furnace, tensions generated during the manufacturing process might be released and, occasionally, produce deformations on large size pieces. To avoid this kind of problem, it is advisable to use high frequency welding procedures, so as to balance the tensions and prevent the release during the galvanizing process. Other stabilising methods can be used, but this is the most economical system.
In the manufacturing of welded components it is necessary to remove the spatters as they will be stuck to the surface and, after galvanizing, they will produce rough spots and imperfections and therefore a poor finishing. All parts and components must be as clean as possible.

On flat components with large contact surface in-between and with narrow slots, discontinuous welding must be avoided so that the water does not penetrate the overlapping surface, thus, anticipating future corrosion. In continuous welding, drainage holes must be provided to ensure safe working conditions and explosion protection, since any air bubbles trapped inside parts dipped into molten zinc (450º) might provoke a blowout in the furnace.

When designing a component that will be galvanized, it is important to bear in mind that a number of holes will have to be drilled on certain points so as to facilitate drainage of the zinc during the immersion. In case of doubt, the best option is to seek advice from our expert galvanizers to help you determine the most suitable place to drill the holes. To a great extent, the selection will depend on the dipping rack or tool utilised to immerse the component into the furnace.

On articles with openings and corners, it is necessary to drill vent holes in hollow areas to prevent the formation of air-bubbles and to allow for complete zinc rinsing. Air bubbles may result in localized uncoated surfaces and, therefore, unprotected areas.

Steel surface must be grease-free for proper galvanizing, as persistent grease may cause black stains on the finished product. This responsibility lies with the customer and not the galvanizer.
At times, paint residues on steel appear as very persistent waste and are hard to remove during the galvanizing process. This makes it necessary to remove them manually or, else, burn them.
Whenever the application of paint onto a galvanized surface will be needed, a special surface treatment will be required; therefore, you should always inform the galvanizer when asking for a quotation.

All of these measures are aimed for an excellent steel surface preparation prior to galvanizing and are of paramount importance for delivering optimum quality and product finishing.

Post-galvanizing recommendations and indications

  • The appearance of hot dip galvanized steel can vary from piece to piece, or even section to section depending on the chemistry of the steel pieces, surface condition and thermal impact of previous treatments, such as mild or annealed steel.
    As stated in standard EN ISO 1461 point 6.1”the appearance of darker or lighter areas or certain irregularities, do not constitute a reason for rejection”. Likewise, stains produced by wet storage consisting mainly of Zinc oxide do not constitute a reason for rejection, provided the thickness of the zinc-steel alloy generated remains above the minimum specified level.
  • If you need to smooth or sand any galvanized steel part, make sure the zinc coating layer is not removed, or else, it will lose its protection against corrosion.
  • As specified by European standard EN ISO 1461, inspections for acceptance must be conducted at the galvanizing plant. Therefore, once the material is taken out of the plant, galvanizers do not take responsibility for any damages caused by the wrong handling, shipping or storage of said material. This principle also applies to other galvanizing standards.
  • Prices are always applied to items weight after galvanizing, as assessed by a certified scale.

Other interesting information

Corrosion categories as per standard EN ISO 14713

Corrosion category
Corrosion speed of Zinc μm/year
Internal side: dry
<= 0,1
Internal: Occasional condensation External: Outdoor exposure non-coastal local areas
0,1 to 0,7
Internal: High humidity, slightly polluted air External: Inland urban or mild coastal areas
0,7 to 2
Internal: Pools, chemical plants etc… External: Inland industrial or urban coastal areas
2 to 4
External: Highly wet industrial or high salinity coastal areas
4 to 8

EN ISO 1461 Table. Minimal allowable thickness on galvanized coating

Spot minimal coating Average coating
Article thickness
Steel > 6mm
Steel > 3 until ≤ 6mm
Steel ≥ 1,5 until ≤ 3mm
Steel < 1,5mm
Castings ≥ 6mm
Castings < 6mm

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