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”.
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.
Fig. 1. Coating thicknesses required by EN ISO 1461: 2009.
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.
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.
Fig.3. Hot-dip galvanizing of thin sheet - coating thickness
* Coating on both side of a square meter.
** Coating in microns on one side of the sheet (only for information).
In Sweden, sectoral standards for the following aspects are given:
Coating thickness control
Sectorial standard - Cleaning after galvanizing (in Swedish)
Sectorial standard - Coating thickness control (in Swedish)
Sectorial standard - Coating adherence testing (in Swedish)