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Painting Problems and Solutions

What is it?
  • Blue-black shiny surface that is initially strongly bonded to the steel. Generally associated with hot rolled steel sections like angle iron and plate.
Possible Causes
  • Steel sections and plates are produced by rolling steel while still red hot. The steel reacts with oxygen in the air to form oxide scales.
How Can I Fix This Problem
  • Mill scale is a reasonably inert material in principle and might prove to be highly protective coating if it adheres well. However, it can be brittle and during handling of steelwork, parts of the scale tend to flake off with comparative ease.
  • Mill scale sets up a galvanic corrosion cell when in contact with steel. Consequently at breaks in the mill scale quite deep pitting corrosion may occur and at the edges rust creep will start which will appear inconsistent and patchy as seen in the photo above.
  • In most cases it is advisable to remove mill scale prior to painting by means of abrasive blast or acid pickling
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