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AASTHO hot dip galvanized

AASTHO (American Standards ASTM A-123)

Standard specifications for zinz coatings (hot dip galvanized) on iron and steel products.

What is it? What does it consist of?

This specification covers the requirements for zinc coatings (galvanization) by the hot-dip process on iron and steel products made of rolled and forged sections, castings, plates, bars and straps.

This specification covers both fabricated and unfabricated products, for example, assembled steel products, structural steel fabrications, large tubes already bent or welded prior to galvanizing, and wire work fabricated from uncoated steel wire. This specification also covers steel forgings and iron castings incorporated into parts manufactured before galvanizing or that are too large to be centrifuged (or otherwise manipulated to remove excess metal from the galvanizing bath).

This specification covers those products previously mentioned in Specifications A 123-78 and A 386-78.

This specification does not apply to galvanized wire, pipe, tube, or sheet steel in specialized or continuous lines or to steel less than 22 gauge (0.0299 in.) [0.76 m] thick.

Galvanising of hardware

The galvanising of hardware which is to be spun or otherwise manipulated to remove excess zinc (such as bolts and similar fasteners with thread, castings, and rolled, pressed and forged items) shall be in accordance with Specification A 153/A 153M.
Fabricated reinforcing steel bar assemblies are covered by this specification. Galvanising of separate reinforcing steel bars shall be in accordance with Specification A 767/A 767M.

This specification is applicable to orders in either inch-pound units (such as A 123) or SI units (such as A 123M). Inch-pound units and SI units are not necessarily exact equivalents. Within the text of this specification and where applicable, SI units are shown in parentheses.

Each system shall be used independently of the other without combining values in any way. For orders in SI units, all tests and inspections shall be made using the metric equivalent of the test or inspection method as appropriate. In the case of orders in SI units, these shall be determined at the galvaniser at the time of placing the order.

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Coating Properties

Coating Thickness – The average coating thickness for all controlled specimens shall be in accordance with the requirements of Table 1 for the categories and thicknesses of material to be galvanised. The minimum average coating thickness for any individual specimen is one coating class less than that required in Table 1. When galvanising products consisting of several thicknesses or material categories, the coating thickness classes for each thickness range and material category shall be as indicated in Table 1.

For orders in SI units, the values in Table 1 shall be applicable as metric units in micrometres. For orders in inch-pound units, the measured value shall be converted to coating class units using Table 2. The specification of coating thicknesses heavier than those required by Table 1 shall be subject to mutual agreement between the galvaniser and the purchaser. (Figure 2 is a graphical representation of the sampling and specimen delineation steps and Figure 3 is a graphical representation of the coating thickness inspection steps).

Table 1. Minimum average coating thickness class by material category.
All controlled samples

Steel thickness range (measured) inches (mm)
Material category <1/16 (<1,6) 1/16 a <1/8 (1,6 a <3,2 1/8 a 3/16 (3,2 a 4,8) >3/16 a <1/4 (>4,8 a <6,4) ≥1/4 (≥6,4)
Structural plates and sections 45 65 75 85 100
Strip and Bars 45 65 75 85 100
Pipe and Tube 45 45 75 75 75
Wire 45 50 60 65 80

Table 2. Coating thickness class

Coating class milipulgadas onza/pie2 μm g/m2
35 1.4 0.8 35 245
45 1.8 1.0 45 320
50 2.0 1.2 50 355
55 2.2 1.3 55 390
60 2.4 1.4 60 425
65 2.6 1.5 65 460
75 3.0 1.7 75 530
80 3.1 1.9 80 565
85 3.3 2.0 85 600
100 3.9 2.3 100 705


Sampling of each lot shall be carried out in accordance with the requirements of this specification.

A lot is a unit of production or shipment from which a sample may be taken for control. Unless otherwise agreed between the galvaniser and the purchaser or stated within this specification, the lot shall be as follows: For control at a galvaniser’s facility, a batch is one or more items of the same type and size comprising a single order or a single dispatch load, whichever is smaller or any number of items identified as a batch by the galvaniser when these have been galvanised within a single production shift and in the same bath. For control by the buyer after delivery, the lot consists of a single order or a single dispatch load, whichever is smaller, unless the identity of the lot, established in accordance with the above, is maintained and clearly indicated on the shipment by the galvaniser.

The method of selection and number of control specimens shall be agreed between the galvaniser and the buyer. Otherwise, control specimens shall be selected at random from each lot. In this case, the minimum number of specimens from each lot shall be as follows:

Number of pieces in Number of specimens
3 or less all
4 a 500 3
501 a 1200 5
1201 a 3200 8
3201 a 10.000 13
10,001 and more 20


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