Inspectioneering

Carburization

Carburization involves the absorption of carbon into steel or alloy during operation in a high temperature environment, typically above 1100F (593C). Carbon from the carborizing environment enters the surface of the steel by diffusion, causing the metal to become embrittled and lose creep resistance and toughness. The result is a loss of corrosion resistance and strength and an increased susceptibility to cracking type failures.  Because it occurs in high temperature environments, carburization often affects furnace tubes. It typically occurs when furnace firing is increased to compensate for a heavy coke deposit on the ID of the tube. The increase in temperature and the coke adjacent to the tube wall can produce a highly carburizing environment, in which carbon can enter steel via diffusion.

The conditions behind carburization are well understood, thus it is fairly easy to detect once it has occurred. This can be done by using eddy current or other techniques measuring increased ferromagnetism of austenitic steels. Ultrasonics and radiography can also be used to detect fissuring or cracks in more advanced stages of carburization. To help prevent carburization, industrial coatings are often applied to materials to prevent carbon in the environment from being absorbed into the material. This topic is covered in more detail in API RP 571 - Damage Mechanisms Affecting Fixed Equipment in the Refining Industry.

 

Related Topics

Amine Cracking Ammonia Stress Corrosion Cracking Blistering Brittle Fracture Caustic Cracking Cavitation Chloride Stress Corrosion Cracking Cooling Water Corrosion Corrosion Fatigue Corrosion Under Insulation (CUI) Cracking Decarburization Embrittlement Erosion Corrosion Fatigue Graphitization High Temperature Hydrogen Attack (HTHA) Hydrochloric Acid Corrosion Hydrofluoric Acid (HFA) Corrosion Hydrogen Assisted Cracking Hydrogen Embrittlement Hydrogen Induced Cracking (HIC) Hydrogen Stress Cracking Hydrogen Sulfide (H2S) Corrosion Microbiologically Induced Corrosion (MIC) Naphthenic Acid Corrosion (NAC) Phosphoric Acid Corrosion Polythionic Acid Stress Corrosion Cracking (PASCC) Spheroidization Stress Assisted Corrosion Stress Corrosion Cracking (SCC) Sulfidation Corrosion Temper Embrittlement Thermal Fatigue Wet H2S Cracking

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Articles
  • January/February 2014 Inspectioneering Journal
    By Antonio Seijas at Phillips 66 Company

    Fired furnaces in the petrochemical and refining industry are critical pieces of equipment that can have a major impact on process unit safety, reliability, and economics. They are complex pieces of equipment, where tubes and other pressure boundary components might fail due to relatively short periods of upset conditions.

  • July/August 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Though oxidation and sulfidation are quite prevalent high temperature corrosion mechanisms in many of our process units, we now come to a few that are not very common, but still deserve some attention to make sure they don’t lead to unexpected failures.

  • July/August 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Decarburization is the antithesis of carburization and rarely results in equipment failure. However, surface decarburization is often a sign that something more serious is going on, ie high temperature hydrogen attack (HTHA), which is well covered in API RP 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants.

  • July/August 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Metal dusting is simply a severe form or extension of carburization in which the extensive carbides that form as a result of carburization lead to grains of metal falling out of the tube or piping and being swept away by the process stream.

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