ISO 1461 vs. ASTM A123
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. This specification is essentially equivalent to ASTM A123 and A153, and this article attempts to summarize pertinent similarities and differences between the requirements of each standard as they relate to coating thickness, appearance, repairs, adhesion, inspection, and sampling.
Summary
Hot-dip galvanizing to A123 will typically lead to a final quality which meets or exceeds ISO 1461. However, there may be a reason to know the differences between the two to the letter of the law. The purpose of this article is to help point out some of the subtle differences.
Scope of Specifications
Ordering Information
The purchaser must provide the following:
Materials Suitable for Galvanizing
Zinc and The Galvanizing Bath (Zinc Melt)
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.
For further comparison, a summary of the ASTM A123 coating thickness requirements is provided below.
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.
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:
Adhesion/Adherence
Sampling & Inspection
Inspection Lots
Control Sample Size vs. Lot Size
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.
Test Methods
Repairs
Certificate/Declaration
© 2023 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.
Comments
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?
(AGA)
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: https://galvanizeit.org/hot-dip-galvanizing/how-long-does-hdg-last/in-the-atmosphere/time-to-first-maintenance
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
(AGA)
Khai, The descriptions of each curve, and the data obtained to develop each curve are explained in detail: https://galvanizeit.org/knowledgebase/article/estimating-the-life-of-hot-dip-galvanized-coatings 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.