EPS-processed steel resists rusting when handled/stored such that it does not come into contact with moisture. We warrant this rust-resistance.

This property of EPS-processed steel – rust-resistance with no protective oil or coating – has been proven in the laboratory and actual processing environments.

Here's how it works: carbon steel has trace amounts of manganese, silicon, chromium and aluminum. Acid pickling strips these elements from the surface of the steel and exposes the iron-rich substrate to oxygen and the formation of rust.

With EPS processing, these trace elements remain on the surface and quickly form an extremely thin and stable oxide layer which protects the underlying substrate from exposure to free oxygen. A similar mechanism is what makes stainless steel rust proof, although the constituents of stainless steel yield more robust rust resistance.

Also, an additive is used in EPS system liquid to reduce "smut" on the finished strip This additive has a rust inhibitor, a residual amount of which remains on the surface after rinsing. It has no impact on paint performance, but is believed  to enhance EPS' rust resistance.

Finally, acid pickling leaves trace amounts of chloride salts on the surface that is a result of the HCl's reaction to the metal.  These chloride salts can result in early and catastrophic paint failures.