Be aware of the potential for metal dusting in high temperature environments or risk severe material degradation!
Although limited to specific environments and temperature ranges, 'metal dusting' can lead to rapid degradation/thinning of material operating in high temperature environments.
The material degradation due to metal dusting is typically characterised by localised pitting and thinning of the material, with the formation of a ‘dust’ like product as grains spall from the surface of the degrading material. This phenomenon can be described as a form of carburisation that can be distinguished from others in that it occurs randomly in localised areas and spreads more rapidly.
A number of mechanisms of metal dusting have been described for various metals, however broadly speaking metal dusting is caused by carbon, from the gaseous atmosphere, being absorbed at the surface of the metal, saturating the surface material with carbon. This results in the formation and growth of high carbon/graphite deposits on the surface/grain boundaries and the subsequent degradation of the metal at the surface as these deposits grow.
The temperature range in which metal dusting occurs is roughly between 450-800°C, however this range can differ depending on the environment (reducing, oxidizing, alternating between reducing and oxidising, etc). Increasing or decreasing the temperature out of the range of susceptibility for the particular material can stop/prevent the degradation. The conditions in which piping/components in the petrochemical industry, particularly in the production of synthesis gas, operate are particularly susceptible to metal dusting, where even highly specialised metals, including various stainless steels and nickel-based alloys, can fail by rapid material wastage.
The rapid material degradation of highly corrosion resistant alloys, may have attributed to the mystery that has been associated with this phenomenon. There is no absolute prevention for metal dusting, however a number of methods, such as altering the operation conditions (temperature/composition), adding Sulphur to the local environment, upgrading the material and the application of coatings, can be used to control it.
Published in Technical Tips by Origen Engineering Solutions on 1 May 2016