Primary Factors Influencing Weathering Steel

Primary Factors Influencing Weathering Steel

Primary Factors Influencing Weathering Steel The performance of weathering steel depends on the proper formation of a dense layer of corrosion product to protect the steel from further atmospheric corrosion. Initially, the corrosion rate of weathering steel is similar to that of plain carbon...
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Primary Factors Influencing Weathering Steel

The performance of weathering steel depends on the proper formation of a dense layer of corrosion

product to protect the steel from further atmospheric corrosion. Initially, the corrosion rate of weathering

steel is similar to that of plain carbon steel; however, wetting and drying cycles, or natural weathering,

causes weathering steel to develop a dense oxide layer, or patina, on the exposed surfaces. This dense,

well-adhered patina helps to slow additional rust formation and the corrosion rate of the weathering steel

stabilizes. The development of the weathering steel patina may be influenced by factors such as:

 Environments

o Urban, suburban, rural, marine, industrial, etc.

o Humid or dry climates

 Microclimates

o Sheltered or bold exposures

o Structure geometry (orientation, angle of exposure)

o Atmospheric pollutants

o Time of wetness

o Traffic below (volume, speed, type, etc.)

o Chloride Exposure

 Design details

Weathering steel structures will perform best in Iowa when they are placed at sites with bold exposures

(exposed to sun and weather without sheltering), are not exposed to chlorides or extended periods of

wetness, and are properly detailed to avoid ponding moisture, dirt, and debris. Nearly all of the weathering steel bridges in Iowa have been constructed in the past 20 years. Based on the observations

during our field investigation, these structures have been properly detailed in accordance with the

recommendations presented in the FHWA Technical Advisory, including using narrow flange widths,

coped stiffeners, water diverter plates, painted girder ends, and integral abutments, as well as eliminating

unnecessary cross frames, stiffeners, lateral bracing, and scuppers. These improved design details help to

reduce potential sources of chloride contaminated water as well as limit areas where water is allowed to

pond on the steel surfaces.

Because the vast majority of the bridges in Iowa are properly detailed, we believe the performance of

weathering steel structures in Iowa can be reduced to three primary factors:

1) heavy exposure to deicing salts,

2) extended periods of wetness,

3) the exposure environment. These three factors often go handin-hand. For example, bridges in urban environment often have a sheltered exposure and are subjected to

chlorides and wetness when traffic “spray” causes chlorides, moisture, and debris to be deposited on the bridge structure. In rural environments, the bridges may still be subjected to salt/moisture spray from

traffic below; however, the open land surrounding the bridge site results in a bolder exposure as the

structure is exposed to sun, wind, and rain from various directions. As a result, weathering steel structures

in rural environments are performing better than structures in urban environments.

While these three primary factors affect the overall patina development at various weathering steel bridge

sites, these factors also affect the development of the patina at various locations within a single bridge

structure. In the “splash zone,” chlorides and moisture often settle onto the top surface of the bottom

flange along with dust, dirt, rust flakes, bird droppings, and other debris. This contaminant layer is

commonly referred to as a “poultice” that retains moisture and keeps chlorides in close contact with these horizontal surfaces. As a result, poultice corrosion was a common observation on horizontal surfaces

above traffic or in areas where water and dirt could migrate and settle outside of the splash zone.

Conversely, the fascia girder is often exposed to direct sun and rain that results in frequent washing of the

patina. This frequent natural washing reduces the chloride contamination on these surfaces, thus

improving the performance of the weathering steel patina. The Iowa bridge structures visited as part of

this project exhibit varying degrees of patina performance.

Product Name

Primary Factors Influencing Weathering Steel

Brand Name

GNEE

Material

Carbon Steel, Corten Steel, Stainless steel

Surface Finish

Rust, Bare, Powder Coated, Polished, Black Heat-resisting Paint, Iron Oxide

Item Number

GN-FP 1101

Size

Diameter : 320mm--1200mm

Thickness : 1.2mm--3.0mm

Package

Inside : Anti-wear foam paper

Outside : Plywood box

MOQ

1 Piece

Sample

Free (without any condition)

OEM & ODM

Customized service is available.

Primary Factors Influencing Weathering Steel

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