This phenomenon is more likely to occur
① Where pieces of metal are in contact.
② On stored metal covered with a plastic sheet.
③ In certain storage conditions when steel is coated with non-rust-preventive oil.

These stains are said to be caused when some areas of a non-uniform coating of oil absorb more moisture than others. Stain-causing chemicals are apparently electrically attracted to non-uniform areas, where they react with the surface of the steel.

Staining is even more likely to occur if the steel is very close to another piece of steel or vinyl sheet.

To help prevent such stains, we recommend spraying or immersing steel in CP-4000 rust inhibitor. It significantly weakens the reaction if chemicals that cause these stains become attracted to non-uniform areas of the coating.

Oil stains with or without CP-4000

Please consider using CP-4000
① When storing steel in hot, humid weather or climates.
② When flat steel surfaces considerably overlap.
③ When the shipment of steel products is delayed.