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Tighter specifications will make steel products last

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article image Greg Wallis.

TECHNICAL specification documents on many public and private projects often overlook an important aspect of steel preparation that greatly increases the lifespan of items manufactured from this metal.

Pre-treatment, a key factor in preserving lifespan of powder-coated steel in mild to harsh conditions found in abundance in Australia, is not only rarely specified as part of a project it is almost never done so reflecting Australian Standards, according Greg Wallis, managing director of metal treatment specialist Custom Built Sheet Metal (CBSM).

"In the cases when pre-treatment is itemised, there is rarely a mention of the type necessary nor its capacity to withstand the elements,” Mr Wallis said.

"Zinc phosphate is considered the best pre-treatment for steels and is recommended by the current Australian Standard AS 4506 :1998.

"Thus, we find that more and more projects using steel in applications subjected to extremes of heat, cold, moisture, chemicals and pressure are resorting to zinc phosphate over iron phosphate coatings.

"But specifiers in Europe normally go a step further, insisting that a powder coated item should withstand a salt spray test lasting, say, five hundred hours because it is eventually expected to last for 15 years in desert conditions, or deep snow.

"The importance of such an exacting prerequisite can never be understated as it is well known around the world how Australia suffers the full spectrum of environmental conditions, often at extreme levels.

"Lack of specification detail is leading to a situation where a totally unsuitable powder coating is given to anything from fire extinguishers, telephone exchange boxes, and fuel pumps, to steel used on skyscraper facades, industrial cool rooms, public furniture, building peripherals - almost anything using steel as a base," Mr Wallis said.

Contained within the guidelines of Standard AS 4506:1998 is a sub-component on coating thickness requirements outlining that any steel substrate subjected to an exterior application requires a zinc phosphate or chromate pre-treatment coating to maximise product/component lifespan - 40æm deep in mild to moderate conditions, and up to 60æm in tropical or severe conditions.

Although corrosivity is generally quite low in tropical regions, the aggressiveness of the environment to organic coatings means special protection is required, states the Standard.

Industrial environments, particularly near smelters associated with the steel industry, require that coating systems be resistant to mild acid.

Coastal salts of marine environments - which embodies most parts of populated Australia - also necessitates a performance coating for long-term protection.

"People within industry too often perceive powder coating as one and the same," Mr Wallis said.

"But because we are equipped to provide both zinc phosphate coating and iron phosphate coating, our company remains closely attuned to the Australian Standard when consulted on steel coating matters.

"An example of appropriate planning was evident from the specifiers of the M5 Eastern distributor construction.

"Knowing that the tunnel would be subjected to air flowing from the Cooks River catchment area as well as some natural seepage of urban acid rain, the engineering requirement insisted on a 20-year lifespan from its fire fighting equipment as anything less posed potential liability in case of failure during an emergency.

"But even at a basic level, items such as street furniture should be, but often are not, zinc coated - hence their frequent and costly replacement at local council level.

"Powder coating on steel is only as good as its pre-treatment, and an unsuitable pre-treatment can be a very costly mistake," Mr Wallis said.

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