1. Overview

Atmospheric corrosion resistant steel, or weathering steel, is a low alloy steel with small amounts of Cu, Cr, Ni, P and other metalloids added to strengthen the corrosion resistance quality. Weathering steel is 4 to 8 times more resistant to degeneration. Like general steel, rust forms initially when exposed to air but a protective surface film sets in an oxidizing atmosphere, minimizing a further formation of rust. Thus the highly adherent and very thin oxide film on the metal surface serves as a protective barrier against any more corrosion. General Steel (SM490B) Weathering Steel (SMA50BW)

2. Standards and Key Features

Classification Standard(KS)               Features Weathering Steel for Welding (KS D 3529) Weathering Steel for Painting SMA00P Compared with general steel for painting, the repainting period is 1.5 to 2 times longer. Non-Painted Weathering Steel SMA00W Can be used without additional painting No need for repainting, thus reducing maintenance costs, and more environmentally friendly (water source protection area) High Atmospheric  Corrosion Resistant Steel  (KS D 3542) SPA-H SPA-C Most resistant to corrosion -Used for wall sidings, road facilities, containers, railcars and other lightweight steel structures

3. Merits and Demerits

Items Remarks Merits Economical Easy maintenance Environmentally safe  Workability Simple construction Initial and life-cycle cost saving analysis Appropriate for those places where repainting is dangerous No need for future maintenance repainting, 100% recyclable Easy transportation and handling No need for initial painting Demerits Unattractive initial appearance For areas that need special aesthetic value, an option of stabilized rust layer can be considered.

4.Applied Technology

Application Conditions for Uncoated Weathering Steel

Climate and Environmental Limitations
1) Salt concentration level in the atmosphere
   → Air-borne salt contamination 
  ot recommended if the marine environment has air-borne salt contamination level exceeding 0.1 mdd (mg/100§²/day)
   →Recommend moving to a location 2Km away from the sea coast 

2) The length of time exposed to wetness
    If the average time of wetness exposure exceeds 60 percent of the year,  weathering steel use is not recommended.
   →The number of days of exceeding relative humidity of 80%  should be below 220 days per year.

3) Sulfur compounds (SOx, H2S) concentration level
     If the  Industrial complex area has sulfuric acid compounds concentration level going over  2.1 mdd ,then weathering steel
bridge is not recommended

Planning, Design, Construction, and Maintenance

General Considerations
1) Design to prevent clogging and leaking
2) Ventilation concerns
3) Design to prevent accumulation of soil that may contain moisture