City water storage tanks 2

[kenj]

Some of our city water storage tanks were erected in the early 80's. They are about 40ft. in dia. and about 60' high, and set on concrete pads. After erection they were sandblasted and allowed to passivate to a black finish. What kind of steel is this?

 

[TVP]

The steel alloys used for these types of construction projects (bridges are the prime example) fall under the classification of "weathering steels". These steels are alloyed with copper and phosphorus for improved atmospheric corrosion resistance and solid solution strengthening. Silicon also positively affects corrosion resistance and strength.

The weathering steels are part of the larger classification of High Strength Low Alloy (HSLA) steels because they use minimal alloy content, low carbon levels, and controlled thermomechanical processing in order to generate steels that have fairly high strength, good toughness, and are weldable.