Hot-Dip Galvanizing

Hot dip galvanization is today the best steel protection process for steel products. Protective layer is obtained by dipping the products into a molten zinc bath at 450°C and ensure the best results about adherence between coating and substrate thanks to a real alloy characterized by continuous Iron-Zinc alloy layers

Focus on structures durability, seismic resistance, and minimizing environmental impact of production processes brought close attention of many designers and engineers to the best technical option existing today: hot dip galvanized steel structures. Tecnozinco operates in according to the highest quality standards to supply HiQualiZinc standard products. Exams and tests are carried out in according to UNI EN ISO 1461 Standard or in according to Customer’s requests. We can also offer indoor storing, zinc layer thickness reading test and adherence test.

OUR ADVICES

UNI EN ISO 14713 Standard provides information and the right preparations needed to properly proceed with hot dip galvanization process.

Here follows some advices useful in designing and working phases

Reinforcement plates must be properly notched in the corners to let the process fluids drain during the galvanization process

Plate overlapping should be avoided in order to avoid defects caused by process fluids infiltration.

Ventilation holes must be properly dimensioned to ensure the correct galvanizing for pipes and avoid process fluids stagnation
Below a guide chart for holes dimensions:

Pipe diam [mm] Ø min. ventilation hole [mm]
< 25 10
25 – 50 12
50 – 100 16
100 – 150 20
> 150 25

There are many methods to make the ventilation holes on beam with base plate. Here some examples of ventilation holes good enough to avoid notching reinforcement plates

For reinforcement plates in big dimension products, central holes or notching must be considered in advance properly placed and oriented. Load anchoring system also must be considered in advance.

In steel tanks the connection pipes must be designed properly to avoid process fluid stagnation.

FAQ

YES: after studies carried out by Corrosion Department of Marche Engineering University it was proved that hot dip galvanized rebar adhesion on concrete is superior than not galvanized rebar.
By galvanizing rebar is also prevented the well-known issue of reinforcement covering
detachment and the following rebar exposure, typical in most of the reinforced concrete
structures.

This event known as “white rust” is caused by zinc oxidation and it’s considered into reference standard. Moist atmosphere catalyze production of zinc hydroxide, oxide and carbonate in Steel products that just ended galvanization process; all these products doesn’t affect natural protection ensured by zinc layer.

Protection duration provided by hot dip galvanization process is strictly connected to the
environment where products are positioned during their life cycle. To define the duration is needed first to identify the Environment Corrosivity Class.
UNI EN ISO 14713-1 Standard express for each class the corrosivity rate in μm/year:
Lasting galvanization assessment: To explain how the calculation work let proceed with the
following example:

Environment corrosivity class Environment description Thickness decline
μm/anno
C1 Interno edifici riscaldati con atmosfera pulita, per esempio uffici, negozi, scuole, alberghi. ≤ 0.1
C2 Ambienti con basso livello di inquinamento. Sopratutto aree naturali. da > 0.1 a 0.7
C3 Ambienti urbani e industriali. Modesto inquinamento da anidride solforosa. da > 0.7 a 2.1
C4 Aree industriali e zone costiere con moderata salinità. da > 2.1 a 4.2
C5-I Aree industriali con alta umidità e atmosfera aggressiva. da > 4.2 a 8.4
C5-M Zone costiere e offshore con alta salinità. da > 4.2 a 8.4
lm-1 Immersione in acqua dolce. 20
lm-1 Immerse in acqua salmastra o di mare. da 15 a 25

Calcolo della durata zincatura
Per spiegare come viene effettuato un calcolo della durata del rivestimento di un manufatto procediamo con un esempio:
Trave di spessore superiore ai 6mm, installato in classe di corrosività C3

Steel Thickness composing the product Minimum average zinc layer thickness
> 6 mm 85 μm (micron)
Environment corrosivity class Environment description Thickness decline [μm/anno]
C3 Ambienti urbani e industriali, modesto inquinamento da anidride solforosa. da > 0.7 a 2.1

By dividing alloy thickness value to annual thickness loss, the result show the number of years durability: 40 – 120years. It could appear a very large range, but includes potentials aggravating conditions like wind, sand and dew.
Usually the average between the two time limits is used as reference value. In the example C3, 1,4 μm/year loss rate, the final result of durability is 60years.

Zinc bath dimensions are: 12,50m x 1,50m x 3,00m; maximum processable dimensions in single dip are: 12,00 x 1,44 x 2,70 m

Increase of weight is about 3% to 10% depending on chemical composition of the treated steel and on shape and dimension of products. It’s good thing consider the increasing of weight during design process.

So called “cold galvanization” process is not a galvanization process but a simpler painting process performed using high zinc content paintings. There is no alloying reaction during this process and the result is just an exterior layer that perform a basic protection against corrosion not even remotely comparable to hot dip galvanization results.

YES: There are many primers ready to be painted on galvanized surfaces that ensure the anchor of the painting layer to galvanized steel. This kind of surface treatment known as “duplex” gives a better protection than the sum of the singles treatments. Moreover, painting galvanized surfaces can be useful when particular aesthetic effect is required.

Despite the bigger starting cost comparing to other solutions, considering the entire product life cycle assessment the money saving is glaring, in fact is the most used solution for public government constructions.

No: the air into the pipes block the dipping into molten zinc and incorrect ventilation hole positioning can cause major damages to the products and major accident to workers and machineries.

No: the process is carried on by dipping entire products into molten zinc bath. It’s possible to cover small areas (threads for example) using adequate anti-zinc coating but degrading the final result.

SERVICES

sabbiatura

SABBIATURA

verniciatura

VERNICIATURA

trasporto

TRANSPORT

collaudo-spessimetro

COLLAUDO SPESSIMETRICO

test-aderenza

TEST DI ADERENZA