Magnetite is the common names for black ferric oxide (Fe3O4 ), a protective coating the forms on the inside of iron pipe to reduce further rapid corrosion.

Magnetite is sold commercially as a polishing compound and is known as “black rouge”.

Once the magnetite forms on the mechanical seal sliding parts several events can occur that will fail the mechanical seal prematurely:

  • The sliding parts will experience premature wear.
  • The hard oxide film will restrict movement of the sliding components causing the lapped seal faces to open and the hard particles to penetrate between the faces and stick into the softer carbon face.
  • Magnetite will stick into the sliding elastomer (O-ring) causing further damage to the close tolerance-sliding surface.

A red form of magnetite, hematite, (Fe2O3) is also found on the inside of the iron piping we often find in hot water systems. Like the black version (Fe3O4 ) it is also very abrasive.



  • On February 16, 2018