Smog laws beget stainless steel fuel tanks
Tougher environmental laws have triggered a new application for S30400 stainless steel
Nickel magazine, Dec. 01 -- In response to increasingly stringent emission standards in the
United States, several European car manufacturers are fitting certain models bound for U.S. markets (e.g.
Volkswagen Beetle) with stainless steel tanks, reports ThyssenKrupp, a major producer of stainless steel flat
products.
Building the fuel tanks requires about 6,000 to 8,000 tonnes of S30400 stainless steel on an annual basis, the German company says.
The tanks will help car manufacturers conform to environmental laws designed to control smog. The state of California, for instance, has introduced legislation that limits hydrocarbon emissions to two grams per day per vehicle. That limit is set to drop further by 2004, while other states and some European countries are expected to follow California's example.
According to the Environmental Protection Agency (EPA) in the U.S., vehicles account for about 60% of the country's total emissions of carbon monoxide, 31% of nitrogen oxides, 30% of volatile organic compounds, and eight percent of particulate matter.
One source of these emissions is fuel vapour that permeates the walls of conventional plastic tanks at a rate of about two grams per day. Both carbon steel and stainless steel prevent this leakage, but stainless steel has the added advantage of longevity because of its resistance to corrosion -- and since the California legislation requires car manufactures to guarantee zero emissions for at least 15 years or 240,000 kilometres, longevity is a crucial feature. Stainless steel tanks are 100% recyclable.
"This [requirement] is a problem for conventional steel," says Jochen Krautschick of ThyssenKrupp's technical development department. The company notes that anti-corrosion coatings presently available do not allow carbon steel tanks to last as long as stainless steel ones.
For years, plastic has been the material of choice for fuel tanks because it can be blow-molded to fit into almost any space. But new techniques such as parallel-plate hydroforming and hydromechanical sheet forming now allow steel to be manipulated into equally complex shapes.
Since current production is limited, stainless steel tanks cost significantly more than carbon steel or plastic tanks. However, this may become less of an obstacle as performance leads to increased demand and unit costs decline as production increases.
"At the moment, only the vehicles for the U.S. market will have the stainless steel tank," he says, "and that's only cars from the European manufacturers."
But as "zero emission" legislation continues to spread beyond Californian borders (and as long as viable alternatives to the internal combustion engine, such as fuel cell technology, remain a distant goal), demand for stainless steel tanks is expected to grow.
"While the plastics industry and tank system manufacturers have developed new products which reduce
emissions, they fail to match the performance of the stainless steel solution," ThyssenKrupp states in a
press release.
Photo: ThyssenKrupp
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