Australian Steel suitable for Australia’s unique environment
The harsh Australian environment wreaks havoc on the construction industry with an estimated $75 billion in damage each year due to corrosion*. A significant portion of this is preventable. Corrosion is a natural process and understanding the factors that cause corrosion allows a fit for purpose approach to design and material selection. Corrosion can compromise the aesthetics and integrity of a structure. If left unchecked corrosion may consume large areas resulting in pitting, scale and loss of wall thickness. Corrosion can be cost effectively addressed; in a similar way to issues that can occur in other materials such as timber or concrete. For example, durability can be enhanced by applying appropriate barrier protection coatings and/or using sacrificial coatings. Metallic zinc coatings on steel has been used for over a century to provide long-term, durable and cost-effective protection of steel structures. Zinc provides that protection by sacrificing itself in corrosive environments instead of the steel, as it is the more ‘active’ metal.
The durability that can be achieved for a specific structure is an outcome of the coating system selected and the design process based on the consideration of:
- The function and estimated life of the structure
- The environment, contaminants and microclimatic factors
Other factors such as materials, aesthetics and owner’s requirements for each part of the structure need to be taken into account. The corrosion rate of steel and/or zinc coatings has been determined over many years by industry experts at multiple exposure sites in state and territories around the country. The exterior environment is monitored and described in terms of the geography and its proximity to airborne contaminants; such as chemical pollution or salt-spray from the bay, coast or ocean. The corrosivity of Australian environments for steel exposed to the atmosphere has been categorised on a 6-level scale, subject to the rate of material loss in microns (μm). The table below is described in AS 4312 and can be used as a starting point to estimate the durability of exposed structures and the subsequent time to first maintenance.
Corrosivity in Australia described in AS 4312.
|Corrosivity Category||Corrosion Rate Steel μm / year||Corrosion Rate Zinc μm / year||Typical Exterior Environment|
|C1: Very low||<1.3||<0.1||Few alpine areas|
|C2: Low||1.3 to 25||0.1 to 0.7||Arid / rural / urban|
|C3: Medium||25 to 50||0.7 to 2.1||Coastal|
|C4: High||50 to 80||2.1 to 4.2||Sea-shore (calm)|
|C5: Very high||80 to 200||4.2 to 8.4||Sea-shore (surf) /offshore within chemical plants|
|CX: Extreme||200 to 700||8.4 to 25||Shoreline (severe surf)|
Zinc Coatings - Electrogalvanized ALLGAL®
ALLGAL® is preferred by many fabricators who find it easy to weld, with minimal weld fume and a spangle -free appearance, whilst powdercoaters say they like the smooth finish. For a cost-effective and easy product to work with - ALLGAL® coated pipe and tube is your fit for purpose solution.
Orrcon Steel ULTRA-SPEC GAL® ZB135/135 (Z275) Zinc Coating
ULTRA-SPEC GAL® is a coated structural tube compliant to AS/NZS 4792 ZB135/135 (Z275) that provides extra durability to meet the level of corrosion protection as specified in the Building Code of Australia and under the NASH standard for use in residential and low-rise steel framed construction. Galvanised products are used in multiple applications across the housing construction sector so it is best to confirm where the source coil has come from and where the product is made. Customers have indicated their preference for ULTRA-SPEC GAL® as they know it conforms to the requirements under the National Building Code and it is made from Australian sourced BlueScope coil and manufactured in Australia at the Orrcon Steel tube mill in Brisbane. ULTRA-SPEC GAL® provides customers with a surety of source and manufacture of product, traceability and local customer support. For a product that you can be sure meets the standards of your build specifications, ULTRA-SPEC GAL® is a good choice.
|Coating Durability Guide||ALLGAL® ZE50 / 50||Pregal Z275 MSGB ULTRA-SPEC GAL®|
|Description.||Electrogalvanised by Orrcon. Uniform colour||Pregalvanised coil, hot dipped in zinc. ‘Spangle’ pattern.|
|Atmospheric Corrosion Category.||Per side||50g/m2||137.5g/m2|
|Low (C2) Dry, rural, remote from coast.||Medium (5 to 10 years).||Extra Long (> 25 years).|
|Med (C3) Coastal, low salinity. Most city areas.||Short (2 to 5 years).||Medium (5 to 10 years).|
|High (C4) Near surf, but not beachfront.||Very Short ( < 2 years ).||Medium (5 to 10 years).|
General fabrications. Powder coated furniture.
Non-spangle may be preferred.
Very good to weld.
Australian Steel. Up to 6mm
Thicker zinc layer when additional durability is required.
Trailer Chassis Building and construction.
Australian Steel. Up to 3.2mm.
The table below is referenced from the NASH Standards Residential and Low-rise Steel Framing Part 2- Designs, with inclusion of ALLGAL® and ULTRA-SPEC GAL® to identify where these products reflect in that standard.
|DESIGNATION||ATMOSPHERIC CORROSIVITY CATEGORY|
|Description (refer to AS4312 / ISO9223)||Arid / Urban inland||Coastal or industrial with low salinity|
|Corrosivity (AS4312 / ISO9223)||Low||Medium|
|Inaccessible for maintenance|
|Roof framing system – unventilated||ALLGAL®||ULTRA-SPEC GAL®|
|Roof framing system – ventilated||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Wall framing system – unventilated||ALLGAL®||ULTRA-SPEC GAL®|
|Wall framing system – ventilated||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Floor bearers and joists – unventilated||ALLGAL®||ULTRA-SPEC GAL®|
|Floor bearers and joists – ventilated||ULTRA-SPEC GAL®||X|
|Decking / balcony – integral||ULTRA-SPEC GAL®||X|
|Ceiling battens||ALLGAL®||ULTRA-SPEC GAL®|
ACCESSIBLE FOR MAINTENANCE
|Roof battens||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Stumps and Piers supporting main building||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Decking/balcony – independent of main structure||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Verandah beams and rafters||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Verandah posts and stumps||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Carport rafters and beams||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Carport posts||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Lower Storey unlined eaves and pergola rafters and beams||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
|Pergola Posts||ULTRA-SPEC GAL®||ULTRA-SPEC GAL®|
By choosing Orrcon Steel’s ALLGAL® or ULTRA-SPEC GAL® tubular range of products, you can be assured it is manufactured from Australian made BlueScope steel coil and offers a fit for purpose solution for the right environment. Products manufactured that reference and comply with Australian Standards have been produced with Australian conditions in mind. You can trust Australian made steels will be the solution to go the distance. Orrcon Steel is a leading Australian distributor and manufacturer of steel, tube and pipe. Our extensive product range covers RHS, SHS & CHS structural tubular steel. Download a factsheet for further information, visit https://www.orrconsteel.com.au/ or call 1300 677 266 to discuss how we can meet your steel needs.