Takeo Kudo

The Effect of Nitrogen on the Localized Corrosion Resistance of Duplex Stainless Steel Simulated Weldments

Abstract The effect of nitrogen, which is one of the most important elements in duplex stainless steels (SSs), was investigated for resistance to pitting corrosion and stress corrosion cracking (SCC) in various environments. The increase in nitrogen content increases the resistance of the base metal, which results from the improvement in the resistance of the γ-phase, which has lower chromium and molybdenum contents compared to α-phase. Nitrogen is an important element in sustaining the corrosion resistance of the heat affected zone (HAZ), which is heated to 1350 C or higher, because nitrogen promotes the formation of γ-phase during the cooling process after welding and avoids the precipitation of chromium carbides or nitrides at grain boundaries. When the nitrogen content is less than 0.08% in 22%Cr, 5.5%Ni, and 3%Mo base composition, the HAZ has little -γ-phase to lead to the high susceptibility to intergranular corrosion and intergranular stress corrosion cracking (IGSCC) occurs even in a pure CO2-Cl− ...

Stress Corrosion Cracking Resistance of 22%Cr Duplex Stainless Steel in Simulated Sour Environments

Abstract Effect of nickel and nitrogen contents on stress corrosion cracking (SCC) of 22%Cr-3%Mo-base duplex stainless steel was investigated in simulated sour environments with respect to both the...

Crevice Corrosion of Corrosion-Resistant Alloys in Simulated Sour Gas Environments

Abstract Crevice corrosion behaviors of corrosion-resistant alloys (CRAs) with various Ni, Cr, and Mo contents were investigated in conditions simulating the sour gas environment encountered in oil and gas production. Crevice corrosion occurred more easily in a 0.1 MPa H2S environment than in a 1.0 MPa H2S environment. Ni, Cr, and Mo all improved crevice corrosion resistance in electrochemical and immersion tests. The improving effect of Ni and Cr on crevice corrosion resistance reached saturation at 20 percent of their contents. The effect of Mo was remarkable. Alloys containing more than 6% Mo exhibited excellent crevice corrosion resistance, which could not be achieved by the increment in Ni and Cr contents. The onset of the crevice corrosion on CRAs in H2S-Cl− environment was investigated by electrochemically studying the pH drop in the crevice solution and the depassivation pH (pHd). These are considered to determine the extent of crevice corrosion resistance in comparison to that in O2-Cl− environme...

Effect of Cr and Ni on Stress Corrosion Cracking Susceptibility in Ni-Cr-Fe Alloys Under Simulated Pressurized Water Reactor Primary Conditions

The primary water stress corrosion cracking (PWSCC) susceptibility of Ni-based alloys, such as Alloy 600 (UNS N06600), has been much higher than that of Fe-based alloys, such as Type 316 stainless steel (UNS S31600). This phenomenon is generally recognized; however, the effects of Fe, Ni, and Cr are not fully understood. In this study, the effect of Cr and Ni in Ni-Cr-Fe alloys on PWSCC susceptibility was investigated using alloys with a wide range of Ni content. The role of these elements is discussed from the standpoint of grain boundary oxidation. According to the stress corrosion cracking (SCC) test results, high-Ni alloys with low Cr contents had high SCC susceptibility, and the SCC susceptibility in high Ni-content alloys was improved by increasing Cr content. On the other hand, low Ni-content alloys had low SCC susceptibility, irrespective of Cr content. These features agree with the field experience in pressurized water reactor plants. In comparison with the results of SCC tests and immersion test...

Crevice corrosion of duplex stainless steel in simulated sour gas environments

Abstract The crevice corrosion behavior of 22% Cr duplex stainless steel (SS), which has become widely used because of its high strength and stress corrosion cracking (SCC) resistance, was investigated in simulated sour gas conditions. The crevice corrosion is accelerated with increasing partial pressure of H2S and temperature, decreasing pH of the test solution, and the addition of sulfur. The duplex SS was more resistant to the crevice corrosion than AISI 316 SS in the H2S-Cl− environment. A simple model of the crevice corrosion, in which the initiation process and the mode of crevice corrosion were discussed, was proposed. The crevice corrosion incubation time based on this model was calculated, and the effect of the crevice gap and the partial pressure of H2S was clarified. The mode of the crevice corrosion changed with the partial pressure of H2S, which was explained by the stability of the NiS film and the depassivation pH in the crevice.

Corrosion behavior of 25 Pct Cr duplex stainless steel in CO2-H2S-Cl− environments

Effects of environmental factors and alloying elements on corrosion behavior of duplex stainless steels in CO2-H2S-Cl− environments were investigated, and the corrosion resistance of DP3® Alloy (25Cr-7Ni-3Mo), which has been developed for hot sea water heat exchangers, was compared with that of other materials.The corrosion resistance of duplex stainless steels increased with the increase of Cr, Ni, and Mo contents in CO2-H2S-Cl− and CO2-Cl− environments. SCC occurred on duplex stainless steels with Ni content below 6 pct, even in the H2S-free conditions at high temperature. Low-temperature aging treatment increased the susceptibility to SCC of duplex stainless steels with lower Ni content.DP3 alloy is resistant to SCC at least up to the temperature of 250 ‡C (480 ‡F) in CO2-Cl− environments, though the application of this alloy to H2S environments is limited.

In Situ Growth-Stress Measurement of Cr2O3 Scale Formed on Stainless Steels by Raman Spectroscopy

Raman spectroscopy was conducted to evaluate mechanical stress in growing α-Cr2O3 scale upon oxidation of austenitic 25mass%Cr-20mass%Ni and ferritic 17mass%Cr stainless steels at 1173 K in air for up to 24 h. Sintered α-Cr2O3 pellet was heated to 373-1173 K and examined in order to obtain the temperature dependence of the wave length of the major Raman peak. For 1.2 mm thick 25mass%Cr-20mass%Ni steel specimen, compressive growth stress was indicated for α-Cr2O3 scale right upon oxidation and the stress increased until oxidation for 3 h, but it saturated and remained constant thereafter. The growth stress of α-Cr2O3 scale was 0.7 ± 0.1 GPa at 1173 K. For 1.2 mm thick ferritic 17mass%Cr steel specimen, mechanical stress was compressive, but the saturated growth stress was around 0.2 GPa, considerably smaller than the “strong” 25mass%Cr-20mass%Ni steel specimen. For 0.1mm thick austenitic 25mass%Cr-20mass%Ni steel specimen, the test results were similar. These were attributed to the different high-temperature strength of the metal substrate. Hence, for high-temperature oxidation of thin foils and/or ferritic steels of which high-temperature strength of the metal substrate is relatively poor, stress relaxation of protective α-Cr2O3 scale can result and the growth stress of α-Cr2O3 scale may be lowered by the “weak” metal substrate. Raman spectroscopy can offer useful information on the mechanical stress of protective oxide scale even at high temperatures.

Corrosion Behavior of Titanium Alloys in a Sulfur-Containing H2S-CO2-Cl− Environment

Abstract Corrosion behavior of Ti alloy containing Mo and Pd with high-yield strength were studied in S-containing H2S-CO2-Cl− environment at elevated temperature. Ti alloys showed stress corrosion cracking (SCC) susceptibility in this environment, and the susceptibility largely depended on the yield strength of the alloys. It was clarified that the addition of Pd and/or the increase of Mo content in alloys was very effective for improvement of the SCC resistance. These Ti alloys coupled with carbon steel did not have hydrogen embrittlement susceptibility in NACE TM01-77 solution. Localized corrosion resistance of Ti alloys in S-containing sour environment was superior to that of Ni-base Alloy C276. The stability of TiO2 film in sour environment containing elemental sulfur was discussed on the basis of the potential-pH diagram of Ti-H2O system at 200°C.

Precipitation-Hardened, Nickel-Base Alloys for Sour Gas Environments

Abstract Stress corrosion cracking (SCC) in sour gas environments of γ′ [gamma prime: Ni3(Ti and/or Al)] and γ″ (gamma double prime: NiNb) precipitation-hardened, nickel-base alloys has been studie...

Effect of Thermal Treatment on Stress Corrosion Cracking Susceptibility in Alloy 600 and Type 316 Stainless Steel Under Simulated Pressurized Water Reactor Primary Conditions

Under pressurized water reactor primary conditions, the stress corrosion cracking susceptibility of Alloy 600 (UNS N06600) is improved by chromium carbide precipitation in the grain boundaries. However, the effect of chromium depletion on stress corrosion cracking susceptibility is not completely understood. Type 316 (UNS S31600) stainless steel has minimal stress corrosion cracking susceptibility and cold work increases the stress corrosion cracking susceptibility. This study investigates stress corrosion cracking susceptibilities of Alloy 600 and Type 316 SS, which are thermally treated at a temperature of 700°C. Stress corrosion cracking did not occur in Type 316 SS regardless of the thermal treatment conditions. Alloy 600 has high stress corrosion cracking susceptibility with chromium depletion and chromium carbide precipitation. On the other hand, when chromium carbides are precipitated and chromium depletion is recovered, Alloy 600 has low stress corrosion cracking susceptibility. There are some fin...