Lasting Lights
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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DE-ICING CHEMICALS used on highways in northern climates can corrode metal light poles.
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ONE COMPANY in Minnesota, U.S.A. has been making stainless steel light poles such as this for 45
years.
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RIVETS CONNECTING the poles to the base are made of S31600 stainless steel in order to meet shear
requirements.
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ABOUT 70% OF TOPPLED POLES can be refurbished.
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Corrosion-resistant stainless steel outlasts the elements
By Carroll McCormick
Nickel Magazine, March 2006 -- Sales of stainless steel light poles have increased in the past five to seven years in the snow belt in the United States, according to one of the country’s leading light pole manufacturers.
Constructed mainly from S20103, with a 4.5% nickel content, the light poles have much to offer, including light weight, zero maintenance, excellent corrosion and vibration resistance, and an expected life span of a century. Moreover, if damaged beyond repair in a highway accident, they’re recyclable.
"Departments of Transport [DoTs] are continually looking for more effective de-icing chemicals to melt ice and snow quickly," says Trevor Millerbernd, vice-president and chief operating officer of the Millerbernd Manufacturing Company in Winsted, Minnesota, U.S.A. "On roads, over the past three to five years, DoTs have used mixtures that are considerably more aggressive than sea salt."
Dick Clark, Millerbernd’s marketing manager, says the company has been building stainless steel poles for about 45 years and hasn’t had a single corrosion-related failure.
Stainless steel light poles account for about 10% of Millerbernd’s total output of standard and custom light poles.
The company uses S20103 in the pole shafts, with a wall thickness of typically either 1.83 or 2.77 millimetres. The stainless steel in the transformer-bases (t-bases) is 2.77 mm thick. When S20103 plate is unavailable, S30403, with a 10% nickel content, is used.
"We use S20103 because it gives excellent performance and is cost-effective," says Millerbernd, "so wherever possible we try to use it." Adds Clark: "A key reason for using S20103 is malleability; it takes considerable power to form a stainless steel pole."
Other components, such as luminaire mastarms, are constructed out of 5.08-mm-thick S30403, again, because it’s more available than S20103. For high-mast lights, which can soar 48.8 metres over the road, the lowering cables, winch drums, luminaire rings, and other mast head components are fabricated from S20103 and S30403, depending on the availability of raw stock.
The rivets connecting the poles to the breakaway bases are made of S31600 so as to meet the shear requirements of the American Association of State Highway and Transportation Officials, the ruling body for U.S. highways.
Clark points out that once a pole shaft material, whether aluminum, carbon steel, stainless steel or fibreglass, is on the "approved" lists of some DoTs, these materials must all be regarded as equal, and the lowest bid may reign.
"The price of stainless poles is competitive with aluminum," says Millerbernd. "We compete with the other materials day by day." And as Clark explains, some people think that if they buy a pole that lasts 25 years, that’s long enough. "But it’s not uncommon to see aluminum bases that are damaged heavily by roadway salt, and carbon steel t-bases starting to corrode after 15-20 years. Nor is it uncommon to hear a design group say: ‘I didn’t know that anyone manufactured stainless steel poles.’"
Stainless steel light poles have additional advantages: Because of the higher yield strength of stainless steel, they can be made with a thinner wall thickness, and are lighter than aluminum or steel poles. Also, about 70% of toppled poles can be refurbished by Millerbernd for re-use.
"We don’t know of other types of poles that are refurbishable," says Millerbernd. "Knockdowns are frequent, so refurbishing the poles is great interest to our DoT customers. From the recycling standpoint, stainless steel will bring a fairly reasonable price."
Millerbernd also makes stainless steel t-bases to which customers bolt carbon steel poles salvaged from carbon steel t-bases that have become corroded beyond repair.
Stainless steel poles are often chosen for bridge decks and medians where there is high vibration, as they do not require the vibration dampeners necessary with softer pole shaft materials. They are also frequently specified for non-DoT applications where corrosion-resistance and their pleasant as-finished colour are desired.
Although the poles require no further treatment beyond the matte finish obtained by blasting them with stainless steel shot (a non-reflective finish is safer for roadside applications), some are painted to match municipal colour schemes. Since stainless steel can stain, particularly in coastal environments, Millerbernd recommends a clear coat if clients place particular value on a decorative finish.
But in the snow belt of the U.S., where sales are booming, it all adds up to zero maintenance and long life.
Carroll McCormick is a Montreal-based freelance writer.
PHOTOS: Tom Skudra for Nickel Institute (top) and Millerbernd Manufacturing Co.
Dick Clark |
