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One of my customers has asked me to galvanize his product according to ISO 1461. Is this specification different from ASTM A123? And, if so, what are the differences?

*Updated in 2022


International Standards Organization ISO 1461, Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications and Test Methods, is a general galvanizing specification. Hot-dip galvanizing to A123 will typically lead to a final quality which meets or exceeds ISO 1461.

This article provides a basic overview of the similarities and differences between ISO 1461 and A123 as they relate to coating thickness, appearance, repairs, adhesion, inspection, and sampling. It is not intended to be used as an exhaustive guide on the differences in terms of inspection requirements or contractual obligations when substituting one specification for the other.

Scope of Specifications

ISO 1641 Scope

Ordering Information

The purchaser must provide the following:

ISO 1641 Ordering Information

Base Metal Considerations

ISO 1641 Materials

Zinc and The Galvanizing Bath (Zinc Melt)

ISO 1641 Zinc Bath

Coating Requirements

Coating Thickness for Articles That Are Not Centrifuged

The differences in minimum average coating thickness for most steel articles are small. In the specification, the ISO minimum coating thickness requirements are summed up into one table, which does not mention coating grades and does not require the user to reference two tables as with ASTM A123. Also, the ISO1461 specification lists minimum local coating thickness to which any one measurement must meet. These are 0.4-0.6 mils thinner than the minimum average coating thickness. In the ASTM specifications, only ASTM A153 has such minimum local thickness coating listed for castings and fasteners. Rolled, pressed and forged articles referred to ASTM A153 also have minimum local coating thickness; these articles are not specifically mentioned in the ISO specification.

A comparison of the standards finds they are very similar, with the ASTM Specs typically requiring more coating thickness on most types and thickness of steel.

ISO 1641 vs A123

For further comparison, a summary of the ASTM A123 coating thickness requirements is provided below.

A123 table

Resolving Concerns When Galvanizing Low Reactivity Steels

Steels with very low levels of silicon and aluminum-killed steels regularly present a challenge in developing a galvanized coating that meets the thickness requirements of the galvanizing specifications. To address these concerns, both galvanizing standards provide guidance to address occasional instances where normal coating thickness requirements cannot be achieved when galvanizing steels with low reactivity.

ISO 1641 Low Reactivity Steels

Coating Thickness for Centrifuged Articles

The ISO 1461 standard incorporates the ASTM equivalent of A153 regarding centrifuged articles into ISO 1461. It is more difficult to compare the ISO 1461 category requirements and ASTM A153 category requirements side by side for articles not centrifuged. This is because the ASTM material categories are defined through a combination of part size and steel thickness. A comparison of the tables is provided below:

A153 table


ISO 1641 adhesion

Sampling & Inspection

Inspection Lots

ISO 1641 lots

Control Sample Size vs. Lot Size

ISO 1641 test articles

Reference Areas for Coating Thickness Inspection

For each reference area, five or more measurements are made at widely dispersed points to represent the entire surface area of the test specimen.

ISO 1641 reference areas

Test Methods

ISO 1641 test methods


ISO 1641 repairs


ISO 1641 certificate

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Khai Nguyen/ PTSC M&C

Dear Dr. Tom Langill During studying to select the HDG thickness for offshore structure, I recognize there is a large difference between AGA's guide and ISO 14713 -1 related to the HDG lifetime. According to AGA's guide, the "time to first maintenance" of 100-micron HDG in tropical marine environment condition is around 75 years. However, as per ISO 14713 -1, "life to first maintenance" of 100-micron HDG in offshore environment condition is just 8 years. Could you please help me to explain why this difference?


Hello Khai, AGA"s TFM Tropical marine curve does not represent offshore environment condition. AGA TFM chart also does not directly correlate to ISO C1-C5 categories, but instead represents common atmospheric category descriptions experienced in North America. For more information on how the AGA chart was developed:

Khai Nguyen

Dear Dr. Tom Langill Many thank for your quick reply. Now I am clear that the AGA TFM chart does not directly correlate to ISO categories. However, it is easy to see a far difference between AGA TFM and ISO TFM. I would appreciate it if you could advise some points, which may be the roof of the difference. Sincerely. Khai Nguyen


Khai, The descriptions of each curve, and the data obtained to develop each curve are explained in detail: The definition of each ISO category differs, and therefore different data points were used to develop the tables you see in ISO 1461. For more information, refer to ISO 9223 and ISO 14713. This means both resources can be used to assist you in estimating corrosion rates of HDG steel, based on the definitions. Please contact the AGA directly with information on your project and application so we can assist you with corrosion rates which can be used for design purposes.

Khai Nguyen

Dear Dr. Tom Langill It is very helpful. Thank you very much.

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