Assess The Performance Of Weathering Steel

Assess The Performance Of Weathering Steel

Assess the performance of weathering steel In its bare, mature state, weathering steel has a unique, natural oxide protective oxide film about the same thickness as a heavy coat of paint. This protective oxide film is dense, tightly adherent, and relatively impervious to further atmospheric...
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Assess the performance of weathering steel

In its bare, mature state, weathering steel has a unique, natural oxide protective oxide film about the same thickness as a heavy coat of paint. This protective oxide film is dense, tightly adherent, and relatively impervious to further atmospheric corrosion. Minor damage to this oxide film heals itself. Therefore, maintenance is greatly reduced compared to a painted bridge. Bare weathering steel is suitable for many atmospheric environments, including moderate industrial and some marine exposures . Because little or no initial painting or subsequent repainting is required, weathering steel results in significant first cost and life-cycle cost savings. When considering the suitability of weathering steel, engineers must consider the life-cycle cost of the structure, including initial cost, cost of maintenance, repaint interval, and the time/value of money. According to the Transportation Research Board, the calculation of life-cycle cost shows that bare, maintenance-free weathering steel (initial cost only) should be the more economical . Further, S. Frondistou-Yannas estimated, in 1981, that the cost advantage of uncoated weathering steel main girders, compared to painted steel main girders, ranges from 10 to 20 percent depending on the paint system. On an initial cost basis, uncoated weathering steel is less expensive than either painted carbon steel or painted high-strength low-alloy steel, and the difference increases with increasing sophistication of the paint systems utilized. When the costs of future maintenance painting of steel are taken into account, cost advantage of uncoated weathering steel becomes even greater. As an example, it has been estimated that Pennsylvania realized initial cost savings of about $200 per ton for uncoated weathering steel versus painted carbon and high-strength low-alloy steel for a bridge opened in 1988. Life-cycle cost savings of about $1 million (equal to the initial cost of the superstructure) were also projected . Fabricators have reported that painting bridge steels in their shops represents 10 to 15 percent of their shop time. Without painting, fabrication is faster, material-flow and handling throughout the shop is simplified, and the cost of paint itself is eliminated. Further, if maintenance coating can be eliminated or significantly reduced, the costs and public inconvenience of managing traffic flow, lane reductions, or outright traffic closure can also be eliminated. Finally, environmental benefits result from the use of weathering steel. The reduction in initial painting reduces emissions of volatile organic compounds when oil-based coatings are used. The elimination of coating removal and disposal of contaminated blast cleaning debris over the life span of the structure is another significant environmental benefit. In some instances, the estimated cost of the collection and disposal of materials from a structure repainting project were so great that the structure was either abandoned or replaced with a new bridge . The cost savings cited above are only realized if the material performs well. The field investigation of 39 TxDOT weathering steel structures indicates that, despite the lack of an even protective oxide film covering the entire superstructure, the steel is in good condition and is performing well, indicating that the use of weathering steel has provided Texas taxpayers the savings anticipated. According to S. Frondistou-Yannas, there were about 330,000 steel bridges in the U.S. in 1981. Of these, several thousands must be coated every year to protect them from corrosion, while others have to be rehabilitated and repaired because of past inadequate corrosion protection. Moreover, some new steel bridges are built with special steels that are more resistant to corrosion, and therefore are more expensive. Frondistou-Yannas claims that the total corrosion bill paid by taxpayers for steel bridges of hundreds of millions of dollars annually could be eliminated with pertinent, timely, and reliable information on bridge protection

Assess the performance of weathering steel

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