Standards

For hot-dip galvanizing specifications, quality requirements and test methods are given in the following international standard: EN ISO 1461 “Hot dip galvanized coatings on fabricated iron and steel articles – Specifications and test methods”.

General requirements

According to the standard the coating quality, thickness, structure and physical and chemical properties are influenced by steel composition, mass and the conditions during the hot-dip galvanizing process. Requirements for information between galvanizer and customer are specified in a series of appendices to the standard.

Normally the minimum quality requirement regarding coating thickness and surface appearance are in accordance with EN ISO 1461.

To make it possible to fulfill these above requirements, the customer should inform the galvanizer about steel composition and desired coating thickness according to standard.

Article and its thickness	Local coating thickness (min) µm	Mean coating thickness (min) µm
Steel > 6 mm	70	85
Steel > 3 - < 6 mm	55	70
Steel > 1,5 - < 3 mm	45	55
Steel < 1,5 mm	35	45
Castings > 6 mm	70	80
Castings < 6 mm	60	70

Fig. 1. Coating thicknesses required by EN ISO 1461: 1999.

Thicker coatings than required by ISO standards

In some cases, thicker coatings than those defined in EN ISO 1461 may be required. For example, in more aggressive environments or when extra durability is needed. In the Nordic countries thicker coatings may be ordered after agreement between customer and galvanizer. Information about how to achieve thicker coatings is given as a national appendix to EN ISO 1461.

In fig 2, the figures 115, 165 and 215 represent the coating thickness in micrometers at 6 mm steel thickness. In the two other columns, optimal and range values for silicon content which is required to achieve these thicker coatings are given.

 

Coating thickness group (µm)	Optimal silicon level (%)	Silicon range (%)
Fe/Zn 115	0.18	0.15-0.21
Fe/Zn 165	0.25	0.22-0.28
Fe/Zn 215	0.32	0.29-0.35

Fig. 2. Optimal and range values for silicon when higher coating thicknesses are required.

Galvanizing of thin sheet steel

Thin sheet is hot-dip galvanized according to ASTM A525. The Swedish standard follows the zinc coating directives in the American standard, which is used internationally.

Symbol	Coating thickness (min) in g/m2 *		Coating thickness (min) in µm**
350	350	300	(25)
275	275	235	(20)
225	225	195	(16)
200	200	170	(15)
140	140	120	(10)
100	100	85	(7)

Fig.3. Hot-dip galvanizing of thin sheet - coating thickness