Durability of Galvanizing Estimator

Disclaimer

The durability of galvanizing estimator interpolates between corrosivity category distances in AS 4312 to determine the corrosivity of the location. The estimated lives to first maintenance of galvanizing and duplex systems are found using interpolation of AS/NZS 2312.2, and the estimated life to first maintenance of paint only systems are found using interpolation of AS 2312.1. A tool for estimating the life of other galvanized coatings is also provided based on the coating thickness provided in their standards. Many design, site specific or environmental factors can effect the corrosion rate and life to first maintenance of a coating system. These include sheltering from rain washing which will increase the expected rate of corrosion, while sheltering from the surf by islands, topography or buildings decreases the expected rate of corrosion. This tool is meant to provide an estimation only for articles batch hot dip galvanized to AS/NZS 4680, and a detailed site inspection and professional advice should be sought from a coatings professional before choosing a protective coating method.

Please contact the GAA if you would like more information.

Inputs

Location

Distance from the coast (km)
Is the closest salt water influence a surf coast or calm bay?*

*As a guide, a surf coast is an area of saltwater where breaking waves are a normal occurrence on at least four days per week or 60% of the time. Wind-driven white caps or choppy water are not considered breaking waves.

Steel Details

What is the typical thickness of the steel? (mm)

≤1.5

>1.5 to ≤3

>3 to ≤ 6

>> 6*

*Steels much thicker than 6mm can sometimes achieve much thicker coatings than the minimum required by AS/NZS 4680. Only select this option if the galvanizer can achieve a 125 µm coating.

Would you like to compare to the durability of a duplex coating? (Paint over galvanizing)

Please select the duplex coating System Number from AS/NZS 2312.2 Table 7.1:

The paint component of the duplex system chosen consists of 25 µm Acrylic latex primer, 50 µm Acrylic latex paint.

Would you like to compare to the durability to a standard paint only system?

Please select the paint System Designation from AS 2312.1 Table 6.3:

The paint system chosen consists of 40 µm Alkyd primer, 40 µm Acrylic latex, 40 µm Acrylic latex.

Would you like to compare the durability to a different galvanized product?

Other Galvanized Coatings

There are a wide range of other galvanized coatings available and this estimator provides a selection of those covered in AS/NZS 2312.2.

Small steel items can be batch hot dip galvanized and then centrifuged (spun) to remove excess zinc. They have lower coating thickness requirements (listed in Table 2 of AS/NZS 4680) than items that are only dipped, while still meeting all the other requirements of AS/NZS 4680.

Threaded fasteners (bolts, nuts and washers) are batch hot dip galvanized and centrifuged to AS/NZS 1214. There is only one thickness requirement for these products and AS/NZS 1214 is used to galvanize fasteners that meet AS/NZS 1252.1 (property class 4.6, 8.8 and 10.9) and AS 1559 (tower bolts).

Hot dip galvanized coil is produced to AS 1397 and is commonly used as purlins and other roll formed items. As with all hot dip galvanized coil products the method of specifying these products is by coating mass, which is defined as the total mass of coating per square metre for both sides combined. For example, Z350 means a minimum of 350 grams per square metre combined total mass on both sides of the steel substrate. While AS 1397 provides guidance on the coating thickness on each side, it is not a requirement and this estimator assumes the minimum thickness as provided in the Standard. Z350 and Z450 options are provided, as these are the most commonly available purlin sections. Z275 durability estimates can also be obtained by selecting AS/NZS 4792 ZB140/ZB140 which uses AS 1397 Z275 coil as the feed product.

Electrogalvanized coatings are sometimes used in Australia to produce tube to AS 4750. The most common specification is ZE50, which provides a minimum coating thickness of 7µm on each side of the tube. Like all electroplated coatings, these products are rarely used in corrosive locations as the coating does not provide long term protection.

Rectangular (RHS) and square (SHS) tube is sometimes produced using pre-galvanized coil as the feed product to the specification AS/NZS 4792. Two coating thicknesses are readily available, ZB100/100 and ZB140/140 where the number describes the minimum coating mass on each side of the tube. Single sided galvanized tubular coatings are no longer produced in Australia. ZB100/100 uses AS 1397 Z200 coil, while ZB140/140 uses AS 1397 Z275 coil as the feedstock.

Circular (CHS) tube is also produced using a specialised process to AS/NZS 4792 HDG300, which has a minimum coating thickness of 300 grams per square metre on the internal and external surfaces. Typically these products have a thicker coating than pre-galvanized strip, but usually with a lesser thickness than AS/NZS 4680. These products are no longer manufactured in Australia and are often used in street signs and commercial fence posts.

More information is available at the Types of galvanizing and other zinc coatings page.

Please select the galvanized coating:

Non-threaded items batch hot dip galvanized and centrifuged to AS/NZS 4680, with an average single side coating thickness of 35 µm