Requirements for the chemical composition of the steel for galvanizing

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YOU MUST DEMAND YOUR STEEL SUPPLIER TO SELL STEEL WITH RIGHT CHEMICAL CONTENT WHAT IS SUITABLE FOR STEEL GALVANIZATION. DO NOT RISK WITH THE QUALITY!

It is possible to hot dip various of carbon and cast irons, but results may be very different. There will be chemical reaction between steel and zinc layer what improves connection with eachother, but this result is affected strongly with choice of steel. Every steel has is own chemical compositon. In recent past the usage of galvanizing were so rare in our region and steel producers and buyer didn’t had knowledge what chemical content in steel guarantees the best results for galvanization. Eastern metal factorys do not pay attention on the content of the silicon and phosphorus in steels. Unfortunately these two compounds affects most the quality of galvanization. Both Silicon and phosphorus is nessesary alloys without you can not galvanize ,but their content in steel is for quality results is exactly regulated.

Steel with low consists of Silicon (Si < 0,03%) is visually perfect after galvanisation process (shiny and bright) , but it is more difficult to achive the results what is needed for filling the requirements (EVS-EN ISO 1461).

Besides the low content of Silicon it is nessesary to notice the content of phosphorus in steel and witch way steel is rolled.

 

Cold rolled steel:

Si < 0,03% ja Si + 2,5 x P < 0,04%

The consist of Silicon is more important when steel is Hot rolled and less important is the content of phosphorus:

Si < 0,02% ja Si + 2,5 x P < 0,09%

 

If silicon and phosphorus content is more or less than mentioned scope then it fall into so called Sandelini phenomenon (look graphic, Si < 0,15%).

Galvanizing quailty will be very poor with this kind of steel. Zinc layer is very thick and fragile. Surface may peel off.

Steel with avarage content of silicon (Si = 0,15 – 0,22%) are very good for galvanization. Zinc layer is light gray and thickness is allowe by the standard EVS-EN ISO 1461.

Steels with higher content of silicon (Si = 0,23 – 0,30%) may be used to achive more thicker layer of zinc, but must be consider that the zinc layer is more fragile and visually not so good. Extra attention is needed when transporting and loading and unloading these details.

Steels with very high content of silicon Si > 0,30% no longer can use for galvanization. Zinc layer will be very thick ( over 200 µm) and fragile and uneven. Surface may peel of anytime.

Ratio between Si and P content and zinc layer thickness:

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.