Aqueous corrosion problems in energy systems

Because of the ever-increasing trend towards high conversion efficiencies, corrosion in aqueous production and conversion facilities has become more prevalent owing to higher operating temperatures. This has resulted in the development of more corrosion-resistant alloys. However, as the general corrosion (weight loss) problems have been reduced, localized corrosion phenomena such as pitting, crevice corrosion, stress corrosion cracking and corrosion fatigue have become more evident. These corrosion processes now impose limits on the operational efficiencies of many energy conversion systems, and in many cases they represent a financial burden of many billions of dollars to operators. A number of shortcomings in our present knowledge of corrosion science and engineering have been identified. For example, insufficient data are available on the thermo-dynamic properties of aqueous solutions, particularly at elevated temperatures and pressures and for high salt concentrations. These data are required in order to predict materials stability in aqueous systems under extreme conditions, e.g. as found in geothermal and deep sour gas systems. Considerable advances are required in corrosion-monitoring techniques for both research and industrial use. Emphasis should be placed on the development of in situ techniques, particularly methods that are based on electrochemical processes. Also, techniques must be developed for more accurately defining the properties of aqueous systems under extreme conditions. The interaction of environment and stress resulting in subcritical crack growth under both constant-load and fluctuating-load conditions remains a major area of future research if better failure-resistant materials are to be developed. Additional research is required on the application of fracture mechanics to ductile materials and for correlating stress corrosion cracking and corrosion fatigue data. Corrosion control techniques including cathodic protection, anodic protection and inhibitors require further development, especially with respect to their application in aggressive environments. For example, inhibitors offer a possible solution to the "denting" phenomena that are now being experienced in some steam generators and to the strength-failure dilemma facing developers of deep sour gas systems. In deep sour gas systems, inhibitors may be effective in suppressing the tendency of high strength steels to fail in H₂S-containing geoenergy environments or they may permit the use of low alloy materials in aggressive environments which otherwise may exhibit unacceptably high general corrosion rates. Also, considerable advances are required in the simulation of hostile environments in the laboratory so that appropriate fundamental research can be carried out. Finally, we believe that a more comprehensive institutional approach to corrosion research should be adopted. This would necessitate closer cooperation between groups (individuals, laboratories, industries and government bodies) who have a common interest in certain corrosion problems.