High Temperature (or hot) Corrosion involves localized accelerated degradation of metal usually associated with deposition (scaling) of salts or other compounds from hot gases contacting the metal surface.  Several other corrosion phenomena are associated with high temperature corrosion as derivatives of the scaling.  High temperature corrosion often occurs in process units using gases as feedstock or in the hot gas path of gas turbines.  Common types of high temperature corrosion in process plants include:

• Oxidation – deposition of oxides on the metal surface; oxidation can often serve as a protective scale, but can also result in poor thermal conductivity at the oxide-metal interface, leading to other accelerated corrosion problems.
• Sulfidation – deposition of sulfides; sulfide films are not generally as uniform as oxide scale, and can actually attack oxide layers, reducing their protective properties.
• Nitridation – nitriding is often used in alloys to strengthen the material, but in a high temperature processes using nitrogen (e.g., ammonia plant), nitrides deposited as scale or in the form of internal precipitation can produce accelerated localized degradation.
• Chlorination – chloride depositions can be very reactive, destroying other protective scaling or directly attacking the metal surface, and can greatly reduce the expected material properties.
• Carburization – in a high temperature environment in the presence of carbon compounds, the carbon content of the metal may increase, resulting in embrittlement and subsequent cracking and/or failure of components; carburization may also lead to a breakdown and catalysis of carbon to produce metal dusting and to “green rot” in Cr-Ni alloys.  
• Metal dusting – under certain hot gas environments, carbides may form in the metal and subsequently decompose into graphite and metal species, which in turn can act as catalysts for decomposition of carbon monoxide into carbon and oxygen; this condition can result in extremely rapid localized attack and loss of material.
• Green rot – rapid cyclic carburization/oxidation in Cr-Ni alloys that produces a greenish residue of chromium oxide and is associated with significant loss of material.

Quest Reliability has a long history in testing for and characterizing high temperature corrosion damage and has a complementary consulting practice related to materials selection, mitigation, inspection, maintenance planning and general management of these phenomena. 

Quest Reliability’s services specifically related to hot corrosion include:

• Materials ranking and selection for high temperature service
• Mitigation technologies
• On-line corrosion monitoring
• Mechanistic corrosion assessments and failure investigation
• Risk-based inspection
• Condition assessment applications
• Life assessment and life prediction
• Plant life management strategies

Our staff’s knowledge and experience is supported by our testing laboratories where we have the ability to reproduce many of the process conditions associated with hot corrosion.  In addition, Quest Reliability has developed portable non-destructive testing tools and procedures for detection of certain types of hot corrosion in plants, notably detection of carburization in high energy piping or hydrocracking tubes.  Our carburization detection involves a low frequency eddy current technique, coupled with finite element modeling of the electromagnetic wave propagation, correlated with reference measurements and laboratory-based reference data.

For further information about High Temperature Corrosion, please contact us.