Yusuke Minami

Corrosion Resistance of Martensitic Stainless Steels in Environments Simulating Carbon Dioxide Gas Wells

Abstract Martensitic stainless steels (SS) have been used widely for oil-country tubular goods (OCTG) because of their high strength and excellent corrosion resistance in carbon dioxide (CO2) gas wells. Cr-rich precipitates form after tempering heat treatments of martensitic SS. These precipitates can affect the corrosion resistance of martensitic SS in environments simulating CO2 gas wells because Cr is considered to be an important element for improving corrosion resistance. The effects of chemical composition and tempering heat treatments on corrosion rates and pitting potentials were investigated to clarify the effect of precipitates on corrosion resistance of martensitic SS in environments simulating CO2 gas wells. The general corrosion index (GCI = Cr − 12 C + 0.77 Ni + 10 N [mass %]) was confirmed as a good index for estimating corrosion rates of martensitic SS in environments simulating CO2 gas wells. The term “C coefficient/Cr coefficient” (−12), was defined as the amount of Cras carbide precipit...

Field Test Results of Newly Developed Austenitic Steels in the Eddystone Unit No.1 Boiler

Six new grade austenitic stainless steel tubes including SUPER304H® (C.C. 2328), TP347HFG, NF709® , TEMPALOY A-3® , HR3C® (TP310HCbN) and TEMPALOY CR30A® were selected and installed in the superheater of the Eddystone No.1 boiler for the purpose of extending tube service life by reducing fire-side and steam-side corrosion. No significant corrosion was observed on the outer surfaces at 75,075h of exposure. Precipitates due to exposure were identified by TEM-EDS analysis. The thickness of steam oxidation scale was less in high-Cr materials, and high Cr content was thus demonstrated to have effectively improved steam oxidation resistance. HR3C showed comparatively poor impact properties, while the other materials exhibited acceptable impact values of over 30J/cm2 at 20°C. All materials showed reduced creep strength compared with unexposed materials after service exposure under high stress test conditions. However the differences became smaller at lower stresses.Copyright

Properties and Experience of High Cr Austenitic Stainless Steel for Boiler Tubes

Recent boilers for thermal power generation are designed for higher temperature and pressure than in the past, and substantial efforts are being made worldwide to establish technology for ultra super critical power plants. Such boilers will require the use of steels having higher strength and better corrosion resistance than conventional 18-8 austenitic stainless steels. High chromium austenitic stainless steel (22Cr-15Ni-Nb-N) has been developed as a candidate material, and creep rupture strength is more than 50% higher than ASME SA-213 Grade TP347H at 700°C. The hot corrosion and steam oxidation resistance of this steel are also superior to 18-8 stainless steels due to higher Cr content. Thirteen years practical service as superheater tubing in a power plant characterized by high pressure (35MPa) and high temperature (615&°C) has revealed that the mechanical properties and environmental resistance of this steel are sufficient for high temperature boiler tube applications.Copyright

Cavitation Erosion of Pipe Steels

Cavitation erosion often causes the leakage of water in piping systems of industrial plants. In this study, cavitation erosion tests were carried out for the pipe steel specimens fabricated from carbon steel pipes for pressure service, alloy steel pipes and stainless steel pipes. Total 15 pipe materials were tested in a stationary specimen test method using a vibratory apparatus specified by ASTM G32-03 and cavitation erosion were evaluated for each material. It was found that the erosion resistance could be estimated precisely by material hardness.