Carbon, where it does not work

Carbon-graphite is the face that should be the standard in all of your mechanical seals. It can be used in any chemical or combination of chemicals except an oxidizing agent, a halogen and some special applications.

The oxidizing agents will combine with the carbon to form carbon dioxide and carbon monoxide. Here is a list of some of the common oxidizers:

  • Aqua Regia (a combination of nitric and hydrochloric acid) used for dissolving metals.
  • Chloric acid ignites organic material on contact.
  • Chlorous acid, over 200 degrees Fahrenheit (100 C).
  • Ferric chloride used in sewage treatment photography, medicine and feed additives.
  • Hot sulfuric acid, the most widely used industrial chemical.
  • Hydrofluoric acid used for etching, cleaning castings and fermentation.
  • Methyl Ethyl Ketone (MEK) a common solvent.
  • Nitric acid used in fertilizer, dyeing, explosives, drugs, etching and medicine.
  • Oleum used in the manufacture of detergents and explosives.
  • Perchloric Acid - 2N
  • Perchloric acid used in the manufacture of medicine, explosives, and esters.
  • Sodium hypochlorite, used in bleaching paper pulp, textiles, and tanning textiles.
  • Sulfur trioxide used to manufacture sulfuric acid.

Additionally look for any chemical whose name contains the word:

  • Chlorate
  • Nitrate
  • Perchlorate
  • Permanganate
  • Peroxide

The Halogens are another group of chemicals that will attack carbon. They are easy to identify because their chemical name ends in the letters "ine":

  • Astintine
  • Bromine
  • Chlorine
  • Fluorine
  • Iodine

The oxidizer's chemical concentration and temperature will affect the degree of attack. If you are handling any of these chemicals or any chemical you suspect might attack carbon, it would pay to test an unfilled carbon for compatibility prior to installing a mechanical seal.

Recent experience shows that all grades of carbon are no longer being recommended in the following applications:

  • If there is a possibility of color contamination of the product. Some paper, pharmaceutical and paint applications have this problem.
  • If you are sealing hot oil and have to meet fugitive emission standards.
  • Some de-ionized water applications can attack carbon.



  • On February 15, 2018