AskDr. GalvASTM specifications ASTM

A123/A123M, A153/A153M, A767, and A385 all discuss appearance requirements. Although these requirements are slightly different for each specification, they are very similar overall. Here are the summarized appearance requirements of A123/A123M, A153/A153M, and A767:

• Thegalvanizedcoatingmustbefreeofbareareas,blisters,fluxdeposits,andgrossdrossinclusions.

• Globules or excess zinc that willinterfere with the intended use oftheproductarenotpermitted.

• Edge tears or spikes which aredangeroustohandlearenotpermitted.

• Projections or minor surfaceroughnessthatdonotinterferewiththe intendeduseoftheproductarenotrejectable.

You will notice none of these requirements discuss variation in appearance or color, such as mottling (Figures 1 and 2), matte gray finishes (Figure 3), or dark finishes (Figure 4). The appearance requirements of the above hot-dip galvanizing specifications focus on ensuring a quality galvanized coating is applied to the steel, as opposed to visual differences in the color of the galvanized coating. The reason for this is the color differences do not affect the corrosion performance of the galvanized coating.

ASTM A385 is the only batch hot-dip galvanizing specification that discusses variation in appearance or color and states, in general, hot-dip galvanized coatings are specified for corrosion protection rather than appearance. This specification goes on to state the corrosion protection of galvanized coatings with varied appearances is equal for all practical purposes.

It is also important to note touch-up materials can alter the appearance of the galvanizing finish as they are not usually an exact color match. These variations are not cause for rejection. As the galvanized coating weathers over time, variation in appearance due to steel chemistry and touch-up materials will usually assume a more uniform appearance.

But are your customers allowed to reject their galvanized steel when it does vary in color? The answer is no, not according to the above requirements. The only exception is when you agree to provide a galvanized coating with a specific appearance, such as for architecturally exposed structural steel. In those cases, steel selection is usually of utmost importance and a price premium is usually added to the job to account for possibly having to galvanize the steel multiple times to ensure the desired appearance is achieved. These kinds of stipulations should be included in the purchase order.

In summary, your biggest concerns in meeting the appearance requirements of ASTM galvanizing specifications address safety and ensuring a high quality galvanized coating that will provide good corrosion protection is applied to the steel. Your customer can be sure even though visual differences in the coating might exist and are not rejectable, they are still getting a high quality galvanized coating that will last for many years.

Q: What are the appearance requirements of batch hot-dip galvanizing specifications?

A:

Figure 1

Figure 2

Figure 3

Figure 4

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