Other Problems
Carburization
Carburization is the formation of metal carbides in a material as a result of exposure to a carbon containing atmosphere. In some cases, materials are intentionally carburized to impart a high surface hardness and wear resistance. However, in service, it can result in loss of mechanical properties over time in addition to wastage of the material. The corrosion process referred to as "Metal Dusting" is a carburization process which results in surface attack and the formation of a powdery residue.
Carburizing environments are commonly found in process piping and furnace tubes that contain an excess of carbon-containing species which includes hydrocarbon gases or carbon monoxide. Pyrolysis piping in ethylene and olefins plants are prime examples of equipment that must be designed to resist severe carburization.
Resistance to carburization generally can be done using the following mechanisms:
- The establishment of an effective barrier on the surface of the materials that: The barrier is usually a Cr2O3 layer on the material. This is accomplished through the use of Cr as an alloying element. Secondly alloying additions of Ni also help by reducing carbide diffusion in the material.
- Tying up carbon in the material: For this purpose using alloying elements such as Cr, Ni, Si and niobium which are strong carbide formers.
Other Problems will come later