BLOG 6 STEEL & THE ENVIRONMENT


One of the disadvantages of steel is its reaction to certain weather conditions. Due to the presence of iron content in steel, it can corrode and rust up to an extent. 

Extreme weathers have posed a challenge to the architects and engineers and have pushed them to test the limits of the materials. Hence it is really important to impart steel materials only after having the knowledge of the climate pattern of the region and to make an informed decision, based on the conditions.

The physical elements of weather that can affect any metal can be put out as



PHYSICAL ELEMENTS OF WEATHER


Reactions of steel at low temperatures

  • Loss of ductility - plastic deformation
  • Tensile toughness (Increasing embrittlement) - likely to break immediately when a load exceeds its yield strength.
  • Risk of breaking in case of a sudden shock or bending.
  • Increase of the mechanical tensile strength of metal and less elongation at break.

Reactions of steel at high temperatures

  • Temporary loss of tensile strength & ductility.
  •  In stainless steel, high temperatures can lead to the loss of the protective passivating layer.

Factors that speed up the corrosion of steel and other metals are High temperatures, humid weather, Acid rain, galvanic reactions between metals. Corrosion certainly reduces the life-span of steel.

In simple words, Steel expands in high temperatures and contracts at lower temperatures.

Here’s an example of how exposed steel structures react to high temperatures


In 2007, a bridge spanning the Mississippi River in Minneapolis, collapsed, killing 13 people - the bridge was a steel-truss arch bridge - a different design to those studied. (Source: https://www.independent.co.uk/environment/climate-change-us-bridges-collapse-steel-crisis-study-weather-a9169256.html)
“Steel and other metal alloys can be tailored to meet the requirements of an application that is subjected to temperature extremes” 

Steel engineered to resist the effects of weather (e.g. CORTEN Corrosion – Tensile steel) are

  •     Alloys of elements like phosphorous. (other alloys steel - copper, nickel, chromium,)
  •     High in strength
  •     Low carbon

CORTEN steel is also extensively known as Weathering steel. Hence it is used in Facades, fireplaces, steel tanks, sea containers, chimneys, any other steel structure that is exposed or in the exterior structural part of a building. 

Ask how?

-    A protective oxide layer prevents the steel from corroding e.g. Galvanization.

-    Increasing amounts of Chromium and silicon - oxidation resistance.

-    Increasing amounts of Nickel - carburization resistance.

-    Manganese, silicon, nickel, and copper - increase strength.

Various adaptations in steel construction:

Rain
       -   By adding gutters (to the steel) and diverting the water away from the structural steel of the building.
      -  Using alloyed steel metals, as it resists corrosion.

Snow
      -   Planting a few evergreen trees on the windy side of your building.
      -  Simple roof structure to prevent the accumulation of snow.

Hot climate
     -   Alloying of copper, nickel, chromium, phosphorous.
     -   By providing expansion joints.

At low temperatures
     -   Austenitic Stainless steelworks well even at extremely low temperatures like -269 deg C.
 

- Janani Venkateswaran

 No. of words - 486 + flowchart

REFERENCES

Location: India

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