High Temperature (Hf, Y, Zr) Modified Aluminide Coatings for Oxidizing-Sulfidizing Environments

Industrial and power generation processes such as boilers and gasifiers often operate under combustion environments containing gases such as H2S, SO2, O2 etc, which can attack the metallic structure and impose serious problems of corrosion. Corrosion control in high temperature sulfur bearing environments is a challenging problem requiring information on local gaseous species at the surface of alloy components and mechanisms of degradation (sulfidation or erosion corrosion) in these environments.
Recent studies have shown that changes in process conditions may result in thermal cycling and/or environment cycling between oxidizing and sulfidizing environments at the alloy surface. Protective scales are formed during operation, but cycling can damage the scales leading to significant increase in the rate of corrosion. The research focus on exploring the behavior of carbon steel in fluctuating environments between oxidizing and sulfidizing, and develop diffusion coatings (Cr and Al), and RE (Y, Zr, Hf) modified Fe-Al Coatings to reduce corrosion rates. More specifically, the objectives of this research are:

  1. to characterize the local gaseous environments at the surface of alloys in boilers;
  2. optimizing coating parameters to withstand these environments;
  3. understand the underlying failure mechanism;
  4. to improve coating behavior by reactive elements (RE) such as Y, Zr and Hf and precious metal (Pt) additions;
  5. to formulate a plausible mechanism of coating growth and effects of alloying elements on corrosion; and


  1. V. Behrani and P. M. Singh, " Corrosion Behavior of Aluminized and Chromized Carbon Steel in Fluctuating Oxidizing-Sulfidizing Environments", NACE Publications, Corrosion-2007, Paper # 07209.
  2. V.Behrani, J. Mahmood and P. M. Singh, "Mid Furnace Corrosion in Kraft Recovery Boilers and Its Control", NACE Publications, Corrosion-2006, Paper # 06238.
  3. P. M Singh and V. Behrani , “Fireside Corrosion of Carbon Steel Tubes in Kraft Recovery Boiler Mid-Furnace”, NACE Publications, Corrosion-2005, Paper # 05197.


"Factors Affecting The Corrosivity of Pulping Liquors"

Increased equipment failures and the resultant increase in unplanned downtime as the result of process optimization programs continue to plague pulp mills.  The failures are a result of a lack of understanding of corrosion in the different pulping liquors, specifically the parameters responsible for its adjustment such as the role and identification of inorganic and organic species.  The current work investigates the role of inorganic species, namely sodium hydroxide and sodium sulfide, on liquor corrosivity at a range of process conditions beyond those currently experienced in literature.  The role of sulfur species, in the activation of corrosion and the ability of hydroxide to passivate carbon steel A516-Gr70, is evaluated with gravimetric and electrochemical methods. The impact of wood chip weathering on process corrosion was also evaluated.  Results were used to identify black liquor components, depending on the wood species, which play a significant role in the activation and inhibition of corrosion for carbon steel A516-Gr70 process equipment.  Further, the effect of black liquor oxidation on liquor corrosivity was evaluated.  Corrosion and stress corrosion cracking performance of selected materials provided information on classes of materials that may be reliably used in aggressive pulping environments.


  1. " Effect of Black Liquor Oxidation on the Stress Corrosion Cracking Susceptibility of Selected Materials", Corrosion, In press.
  2. "Role of Wood Extractives in Black Liquor Corrosivity", Corrosion, In press.
  3.  "Corrosivity of Sulfide Containing Caustic Solutions", Industry & Engineering Chemistry Research, Submitted.
  4. " Effect of Wood Species on Corrosion of Carbon Steel in Pulp Mills"
    Conference:  16th International Corrosion Congress, September 2005, Beijing, China
  5. " Linking Extractives to Black Liquor Corrosivity"
    Conference:  CORROSION NACE Exposition 2006, March 2006, San Diego, CA
  6. "Downstream Process Effects Related to Wood Chip Pre-Extraction"
    Conference:  TAPPI 2006 Engineering, Pulping, and Environmental Conference, November 2006, Atlanta, GA
  7. "Process Corrosion Related to Wood Chip Extractives"
    Conference:  TAPPI 2006 Engineering, Pulping, and Environmental Conference, November 2006, Atlanta, GA


"Pipeline Corrosion"

Transgranular stress corrosion cracking (TGSCC) is a failure that occurs on buried carbon steel fuel transmission pipelines that are protectively coated and subjected to cathodic protection.  These failures pose a serious threat to public safety and the environment and have a significant economic impact.  Field failure and previous research indicates that hydrogen plays a major role in the TGSCC mechanism.  However, the mechanism by which hydrogen is generated and its overall role in initiation and propagation of TGSCC is not known.    This proposed study accepts that hydrogen has a major role in the mechanism of near-neutral pH TGSCC cracking.  Hydrogen is produced through the reaction of metal ions with carbonic acid and bicarbonate to produce iron carbonate. The objectives of this research are to determine 1) the source of hydrogen generation 2) the effect of environmental variables on diffusion of hydrogen and 3) the method of crack initiation and growth.  If funded, this research will be accomplished by electrochemical test methods such as coupon exposure tests, potentiodynamic tests, hydrogen permeation tests and microprinting. The mechanical aspects of cracking will be studied via compact tensile testing and slow strain rate testing.  The intellectual merit of this research is includes novel information on hydrogen diffusion in carbon pipeline steel, and understanding the environmental variables that influence TGSCC cracking.  This information can be used to have a broader impact by developing better mitigation strategies and detection methods to reduce pipeline rupture, loss of resources, monetary loss, and danger to public. 


  1. S. Asher, P. Singh, J. Colwell, B. Leis. Crack Initiation of Line Pipe Steels in Near-Neutral pH Environments. 16th International Corrosion Congress. 2005. Beijing, China
  2. S. Asher, P. Singh, J. Colwell, B. Leis.  Stress Corrosion Cracking of Pipeline Steels in Near-Neutral pH EnvironmentsCorrosion NACExpo 2006.  2006, NACE International: San Diego, CA.   


"Waterside Corrosion of Boiler Tubes"