AUST – HENDRY building surveyors report that Volume One of the Building Code of Australia (BCA) (Class 2-9 buildings) does not specifically state measures for the protection of structural steel and the determination of individual actions under Part B does not include any reference to corrosive environments. Corrosive environments will include seaside localities and heavy industrial areas.
So how is the required level of corrosive protection determined? The BCA references AS 4100 and AS/NZ 2312, and essentially this task requires the design to have regard to the requirements to a series of Australian Standards. Guidance is provided in Appendix C of AS 4100-1998 ‘Steel Structures’ which references numerous additional codes. AS 4600 Appendix C also provides guidance.
The most informative Australian Standard is AS/ NZS 2312 ‘Guide to the Protection of Structural Steel against Atmospheric Corrosion by the Use of Protective Coatings’. AS /NZS 2312 tabulates a number of coating systems which can be selected relative to the life span of the coating system to its first major maintenance period. This is a significant consideration.
AS /NZS 2312 also provides general design principles and detailing of connections to eliminate inaccessible corrosive pockets. Durability periods in AS /NZS 2312 relate to considerations of the “coating system life to the first major maintenance period”. These are:
Short term 2-5 years
Medium term 5-10 years
Long term 10-15 years
Very long term 15-25 years
Extra long term 25 plus years
AS/NZ 2312 relies on inspection regimes being in place to respond to the performance of the coating system as the periods stated are not guarantees, but rather an averaged anticipated period under ideal conditions having regard to the correct coating application process.
In the first instance, there is no prohibition to the use of most coating systems but durability is a profound consideration for an owner to consider under AS /NZS 2312 . Examples of coating system durability for a breaking surf environment are as follows:
Coating System Durability Table
|Metal Spray Coating||TSZ100||100µm||5-15 years|
|Hot dipped galvanising||HDG900||125µm||10-15 years|
|Hot dipped galvanising plus paint||HDG600||200µm||15-25 years|
|Pre-galvanised strip (tubes)||ZB100/ 100||14µm||Not recommended|
* Epoxy primer PRNC06, 75µm first coat, 125µm high build PRNC13 second coat. Total 200µm thickness of paint finish.
The table of example coating systems clearly shows that owners can be faced with high costs for providing maintenance to structural steel where a lower durability protective coating has been specified in the building’s design. Adherence to AS /NZS 2312 is advisable.
Therefore matching a coating system to the environment and then the period to the first major maintenance period is an important fact to be specified in the building design, with an eye on AS /NZS 2312.
Building Legislation Table
Refer to our Building Legislation table for further information on the building control process.