Technical Info Sheet #9
The vast majority of galvanizing plants work according to the international standard EN-ISO 1461: “Coatings applied by hot-dip galvanizing to iron and steel objects – Specifications and test methods.” The foundation was laid in 1943 with the publication of N 1275 “Hot dip galvanizing of steel or cast iron objects.” The latest version of EN-ISO 1461 is from 2022. This information sheet explains the requirements.
TO ASSESS COMPLIANCE WITH THE REQUIREMENTS MET, AN INSPECTION MAY BE CONDUCTED
An inspection includes these three aspects:
OUTDOOR
Standard EN ISO 1461 says the following about appearance:
DECLOSURE
The coating thickness is the determining factor for protection life. The thicker the coating, the greater the maintenance-free life expectancy! For most atmospheric exposures, there is an almost linear relationship between the two. See EN-ISO 14713-1 for this.
Almost always the coating thickness is determined by magnetic measurement. Table 1 shows the local and average values to be achieved according to EN ISO 1461 in relation to the wall thickness of the steel objects. For centrifuge galvanizing (also called “pendulum work”), the lower values of Table 2 apply. Standard EN-ISO 1461 defines the expressions “local coating thickness” and “average coating thickness” as follows:
In practice, coating thickness measurements are almost always carried out by a non-destructive method; the magnetic method, defined in EN ISO 2178: “Non-magnetic coatings on magnetic surfaces – Measurement of layer thickness – Magnetic method.” The control sample is determined according to the sampling procedure defined in EN-ISO 1461. Within this control sample, EN-ISO 1461 defines “Reference Areas” within which a specific number of separate measurements shall be made.
Remark: Instead of coating thickness, the standard also cites coating mass. Because this destructive method is not or rarely used, it is beyond the scope of this publication.
Note: For pipes galvanized in automated pipe galvanizing plants, EN-10240 applies instead of EN-ISO 1461.
| Voorwerp / dikte voorwerp | Plaatselijke deklaagdikte in micrometer (μm) | Gemiddelde deklaagdikte in micrometer (μm) |
|---|---|---|
| STAAL > 6mm | 70 | 85 |
| STAAL > 3mm TOT ≤ 6mm | 55 | 70 |
| STAAL ≥ 1,5mm TOT ≤ 3mm | 45 | 55 |
| STAAL < 1,5mm | 35 | 45 |
| GIETSTUKKEN ≥ 6mm | 70 | 80 |
| GIETSTUKKEN < 6mm | 60 | 70 |
| Voorwerp met schroefdraad | Plaatselijke deklaagdikte in micrometer (μm) | Gemiddelde deklaagdikte in micrometer (μm) |
|---|---|---|
| > 6 mm tot ≤ 20mm | 40 | 50 |
| ≤ 6 mm middellijn | 20 | 25 |
| Overige voorwerpen (met inbegrip van gietvoorwerpen) | ||
| > 3mm | 45 | 55 |
| < 3mm | 35 | 45 |
Note: If the measured value does not match the values from any of the tables, this may be due to the surface condition of the steel and also its chemical steel composition. Also with High Temperature Galvanizing ((HTV) the coating thickness may be less than mentioned in the tables. The tables are therefore intended for general use.
MECHANICAL LOAD-BEARING CAPACITY (SOMEWHAT SIMILAR TO ADHESION)
There is no suitable international standard to test the adhesion of a zinc coating. Indeed, the adhesion between the steel and the formed zinc layer is not necessarily necessary to determine. After all, the chemical bond between the steel and the zinc is characteristic of the galvanizing process. If proper pretreatment had not been performed, zinc coating formation would also not have occurred. Unlike, for example, with paint coatings, no “detachment” can occur over time. It is therefore usually assessed whether the zinc coating can withstand normal use of the object. This is estimated on the basis of minor damages that have occurred during handling during galvanizing, transport and/or assembly. In this context, it should be realized that minor damages are unavoidable.
CLOSING REMARKS
As this Technical Information Sheet only has a limited and readable scope, we cannot discuss other relevant aspects described in the standard EN-ISO 1461. If you have specified additional requirements in your order, these should be included in the inspection provided they are realistic and achievable.
Should you have additional requirements and wishes in terms of appearance (particularly aesthetic galvanizing), it is a good idea to contact your galvanizing plant as early as the design phase to steer the project in the desired direction. After all, the design, steel order and composition of an object largely determines the final result. It is also important for good and standard galvanizing that the client complies with the design guidelines and recommendations from EN-ISO 14713 part 1 and EN-ISO 14713 part 2 .
EN ISO 1461
Coatings applied by hot-dip galvanizing to iron and steel objects – Specifications and test methods.
EN ISO 14713 part 1
Zinc coatings – Guidelines and recommendations for the protection of iron and steel in structures against corrosion – Part 1: General design principles and corrosion resistance.
EN ISO 14713 part 2
Zinc coatings – Guidelines and recommendations for the protection of iron and steel in structures against corrosion – Part 2: Hot dip galvanizing
EN ISO 2178
Non-magnetic coatings on magnetic surfaces – Measurement of layer thickness – Magnetic method
EN 10240
Internal and/or external protective coatings for steel pipes – Specifications for hot dip galvanized coatings applied in automated plants
TECHNICAL DATA SHEET 2
Procedure for updating
TECHNICAL DATA SHEET 7
Condition of steel surface before hot-dip galvanizing
TECHNICAL DATA SHEET 18
Influence of chemical composition on zinc coating formation
