Investigation of the 0.4C-35Cr-45Ni-Nb Alloy after Service in High-Temperature Steam and Hydrocarbons Environment

The paper presents the results of investigation of the 0.4C-35Cr-45Ni-Nb alloy, which operated in the cracked hydrocarbon feeds and dilution steam at 1125 °C. The material originated from the pyrolytic furnace coil tubes, of which internal walls were in contact with the aforementioned medium, whereas the external walls were in contact with the flue gases. The examination included metallographic and mechanical tests on the material after service exposure, the results of which were compared with the ones obtained for the as-received non-exposed specimens. The metallographic tests revealed changes in the alloy’s structure manifested by formation of significant amount of the carbides due to carburization of the alloy from the steam and cracked hydrocarbon feeds side. The central and external parts of the alloy samples (having no contact with the process medium) underwent substantial degradation but within a relatively narrow zone of the material. The investigations of hydrogen and methane content in the alloy showed a high amount of these gases, resulting from high-temperature corrosion in steam environment. The mechanical tests demonstrated clear shortening of the plastic deformation range of the alloy due to penetration of the gases and formation of the carbides inside the material’s structure. A low level of corrosion and no creep mechanism were detected.

Measurement of creep deformation of ex-service 12% Cr steel using digital image correlation

The effective operation of ageing coal-fired power plants requires routine damage assessment of critical component materials throughout their service history. Traditional post-exposure mechanical testing typically requires large amounts of material for each testing condition. This study introduces an accelerated (high stress and temperature) creep testing technique that employs digital image correlation for strain measurement over a non-uniform temperature field generated by a thermomechanical tester. When applied to different ex-service (exposed to service conditions within a power plant) 12% Cr piping steels, multiple accelerated creep curves at temperatures ranging from 550°C to 600°C are measured from a single specimen for each material condition. Higher creep damage in the steel due to longer service exposure and higher void densities is revealed by shorter rupture times, faster creep rates and tertiary-dominated creep curves when compared to the lower creep damage state. Microstructural study via quantitative electron microscopy confirms the dislocation creep-driven growth of subgrains in the specimen gauge regions relative to the grips. Larger subgrains and a weakening of precipitate distributions for the high damage material were also noted. Digital image correlation–measured strains are in good agreement with traditional techniques of creep testing with standard extensometry. On a comparative basis, the technique is shown to be a plausible form of damage assessment of 12% Cr piping steels with varying levels of service exposure and serve as a suitable mechanical complement to the traditional void replica methodology.

On the effect of long service exposure: changes in microstructure and mechanical properties of Ni-based superalloy

In the present study, the microstructure and the mechanical properties of GTD-111 nickel-based superalloy were investigated. The alloy was in service as the GE-MS9001 gas turbine 1st stage rotating blade for 105,000 hours at a temperature between 950 to 1000 °C. Two sets of samples were extracted from the airfoil and the root of the blade. Then, they were compared for the microstructural and the mechanical properties changes after the high temperature service. Stress-rupture and Charpy V-notch (CVN) tests were conducted on the samples at 871 °C and two temperatures of 25 and 900 °C, respectively. The microstructure and the fracture surface of the samples were analyzed using a scanning electron microscope (SEM). The results showed degradation in the microstructure and the mechanical properties of the airfoil compared to those of the root due to the long-term service at elevated temperatures. The loss in mechanical properties was due to the coarsening of γ’ precipitates and the formation of brittle phases in the grain boundaries.

Effect of Long-Term Service Exposure on the Localized Corrosion and Stress Corrosion Cracking Susceptibility of Type 347 Stainless Steel

The paper presents the results of a study conducted on the effects of long-term service exposure of Type 347 stainless steel (SS) on the microstructure and corrosion susceptibility. The material subjected to the study was in service in a petroleum refinery as heater tube at 620°C for 31 years. The microscopic and x-ray diffraction studies of the service-exposed specimen revealed the precipitation of chromium-rich carbides along the grain boundaries. The microstructural changes that occurred as a result of service exposure affected the ductility and toughness of the alloy. The sensitization of the alloy was assessed by scanning electron microscopy and double loop electrochemical potentiodynamic reactivation. The studies have indicated some degree of sensitization in the alloy. The service exposure resulted in a marginal increase in the susceptibility of Type 347 SS to pitting in environments containing NaCl and NaCl + H2S. Environments such as H2SO4 and K2S4O6 at the tested concentrations did not differentiate between service-exposed and solution annealed specimens for their corrosion susceptibility. Slow strain rate testing of Type 347 SS in both the service-exposed and solution annealed conditions showed susceptibility to stress corrosion cracking in environment containing NaCl + H2S, while the alloy did not show susceptibility to SCC in H2SO4 and K2S4O6. The long-term service exposure did not noticeably influence the SCC susceptibility of Type 347 SS under the tested conditions.

Impact of childhood trauma on risk of relapse requiring psychiatric hospital admission for psychosis

SummaryRelapse in psychosis typically necessitates admission to hospital placing a significant financial burden on the health service. Exposure to childhood trauma is associated with an increased risk of psychosis, however, the extent to which this influences relapse is unclear. This report summarises current research investigating the influence of childhood trauma on relapse requiring psychiatric hospital admission for psychosis. Seven studies were included; two revealed a positive association between childhood trauma and relapse admission, two studies found a negative relationship and three found no significant difference. Inconsistent current evidence suggests a need for further research in this area.