ASTM materials and coatings · Lesson 4 of 4

ASTM materials and coatings: defects, verification and case study

The three defects that make a material callout fail review, how to check a submittal line by line, how the G90 average and single-spot minimums decide a result, and a constructed case where A653 G90 meets AZ55 on A792.

You will be able to: Check a submittal against a specification callout, read a G90 coating weight spot check, and handle a callout that names two different coatings, with the evidence recorded.

11 min · 11 slides · 9 questions

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Slide 1 of 11

Three ways a callout goes wrong

The first defect is the wrong standard: a 55 % aluminum-zinc coating called out to A653, which covers zinc-coated sheet.

The second is a missing or unclear edition, since a standard can be revised and a status can change.

The third is a number read in the wrong system, such as AZ60 taken as the same coating as G60.

Sources

ASTM A653/A653M-25a, Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process (store page: designation, status and scope) - ASTM International
ASTM A792/A792M-25a, Steel Sheet, 55 % Aluminum-Zinc Alloy-Coated by the Hot-Dip Process (store page: designation, status and scope) - ASTM International
GalvInfoNote 1.1, Understanding Coating Weight Designations for Zinc-Based Coatings on Steel Sheet (Rev 4.0, December 2020) - International Zinc Association, GalvInfo Center

Glossary

Single-spot minimum: The lowest coating weight any one reading may show; for G90 GalvInfo gives 0.80 oz/ft², total on both sides, alongside the 0.90 triple-spot average.
Weigh-strip-weigh: The referee method of measuring coating weight: weigh a sample, strip the coating in an inhibited acid, and weigh again; GalvInfo says it is used to check and calibrate thickness gauges.
Equivalency: GalvInfo says no performance equivalency can be drawn between a 55 % aluminum-zinc coating and a galvanized one, so one designation is not a substitute for the other.