ISO 1461

The International Organization for Standardization (ISO) has developed ISO 1461, Hot-dip galvanized coatings on manufactured iron and steel articles - Specifications and test methods, as an industry standard for galvanizing. The standard contains requirements for hot-dip galvanized steel comparable to those in ASTM A123, Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products, and ASTM A153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware. North American specifiers and galvanizers typically use ASTM A123 and A153 for hot-dip galvanizing steel products and fasteners. However, in Canada, the United States and Mexico, the ISO 1461 standard is also sometimes used, which standardizes the European galvanizing industry for both large structural parts and centrifugal hardware.

If a client wants to use ISO 1461 in their project, galvanizers must know what the standard's requirements are and whether they can meet them. As North American galvanizers, the question is: If I galvanize steel to ASTM A123, will I meet the requirements of ISO 1461? The answer is simple: Yes, if the requirements of ASTM A123 are met, those of ISO 1461 are most likely also met. However, galvanizers should be aware of some small differences between the two specifications if They are going to use ISO 1461 frequently. These differences are found in the test methods of the two standards and slight overlaps in coating thickness requirements.

ASTM and ISO standards share similar testing requirements for coating thickness. Both the A123 and 1461 use a magnetic or electronic coating thickness gauge as the primary means of determining the average coating thickness of hot-dip galvanized steel. Both standards also rely on the strip weighing procedure (referred to as gravimetric method in ISO 1461) as an alternative method for determining coating thickness when magnetic gauges are not suitable or as a reference method.

Sampling requirements are very similar between standards. Each standard requires that a certain number of items or samples be randomly drawn from a lot and the coating thickness checked. The number of items or samples to be removed from the lot is determined by Table 1 of ISO 1461, which is exactly the same as the tables found in Section 7.3 of ASTM A123 and Section 6.2 of the standard. ASTM A153. However, the difference lies in how the average coating thickness is determined after breaking down the batch into this control sample.

ISO 1461 requires that after a batch control sample is produced, articles are divided into reference zones. Each reference area uses the average of five measurements within a small area to determine an average. These averages are used to determine the average coating thickness for the entire lot. Instead, ASTM A123 requires that the control sample be made up of specimens. Once the specimens are determined, it is not necessary to break them down further. The A123 standard also requires that five measurements be made on each sample, but these must be spread widely throughout the volume of the sample rather than close together. These may seem like small differences that are probably insignificant to you and your client, but they can be important to know about if a dispute arises.

There are further differences between the standards in the minimum average thickness requirements. These differences can be considered insignificant, and galvanizers will most likely meet the requirements of ISO 1461 if they galvanize to A123. However, there may be a reason to know the differences between the two inside out. The following table helps point out these subtle differences. The table assumes that the steel is being galvanized based on the thicknesses in the left column. This column uses the standard units of mm found in ISO 1461, but can be converted to imperial units. The table below indicates the requirements of ISO 1461 and the thickness of steels whose A123 requirements overlap. Note that ASTM requirements for wire coating thickness never match ISO standards.

As stated above, the differences between ISO 1461 and the combination of ASTM A123 and A153 are quite small. If the steel is galvanized in accordance with ASTM A123 or A153, it will more than likely meet the requirements of ISO 1461. The above information is intended to be punctilious and point out minor differences.