Selection of Flapper Valve Steel for High Efficient Compressor

Due to the environmental, energy saving and economic requirements, development of very high efficient compressors is of great importance. Consequently, flapper valve material becomes a critical issue and a limiting factor for the development of compressor. This paper provides a discussion on the material selection of the flapper valve for the compressors with very high efficiency, based mainly on a basic research on the mechanisms of impact fatigue and a FEM simulation on the formation of stress concentration in the flapper valve during the impact process. Impact fatigue initiation is caused by the initial impact stress, but the fatigue crack propagation is caused by a wavy stress propagation. This causes the formation of secondary cracks at the stress concentration points where two stress waves have the same phase. The results indicate that the flapper valve materials for the very high efficient compressors should have both high impact fatigue strength for the initial stress, and high stress damping capacity to reduce the crack propagation rate. Most recent developed flapper valve steel, Sandvik Hiflex™, shows both higher impact fatigue strength and higher damping capacity comparing with other commercial flapper valve steels available. This flapper valve steel material has successfully been used in the newly developed high efficient compressors recently. Some case stories have been discussed

CONQUER CORROSION : Key issues of the lead-cooled fast reactor design

The lead-cooled fast reactor (LFR) is one of the concepts of the Generation IV reactorsystems. There are some issues that have to be solved before a research orcommercial LFR can be built. The objective of this thesis was to identify these keyissues and analyse them by studying results from previous research: choice of fuel,corrosion on structural materials and corrosion/erosion on pumps.The major fuel candidates for the LFR are MOX fuel (Mixed OXide fuel), metallic fuel,nitride fuel and carbide fuel. Nitride fuel has desirable properties but its production ismore difficult than for MOX fuel.Most of today’s commercial steels are not corrosion resistant at higher temperaturesbut they could possibly be used for an LFR test demonstrator with an operatingtemperature lower than 450 ºC. A new type of steel called oxide dispersionstrengthened (ODS) steel and a new ceramic material MAXTHAL both showpromising corrosion resistance even at higher temperatures.By controlling the oxygen concentration a protective oxide film is produced. Flowingliquid coolant causes erosion and wears down the oxide film. Pumps are exposed tocoolant velocities of 10-15 m/s causing both erosion and corrosion. There is nosolution today, but MAXTHAL shows promising results in tests with liquid lead of lowvelocity. There are also other issues unsolved, such as irradiation damage onstructural materials, thus more research is needed.Economic and political aspects were not covered in this study. This thesis work wasperformed at Vattenfall Research and Development AB

CONQUER CORROSION : Key issues of the lead-cooled fast reactor design

The lead-cooled fast reactor (LFR) is one of the concepts of the Generation IV reactorsystems. There are some issues that have to be solved before a research orcommercial LFR can be built. The objective of this thesis was to identify these keyissues and analyse them by studying results from previous research: choice of fuel,corrosion on structural materials and corrosion/erosion on pumps.The major fuel candidates for the LFR are MOX fuel (Mixed OXide fuel), metallic fuel,nitride fuel and carbide fuel. Nitride fuel has desirable properties but its production ismore difficult than for MOX fuel.Most of today’s commercial steels are not corrosion resistant at higher temperaturesbut they could possibly be used for an LFR test demonstrator with an operatingtemperature lower than 450 ºC. A new type of steel called oxide dispersionstrengthened (ODS) steel and a new ceramic material MAXTHAL both showpromising corrosion resistance even at higher temperatures.By controlling the oxygen concentration a protective oxide film is produced. Flowingliquid coolant causes erosion and wears down the oxide film. Pumps are exposed tocoolant velocities of 10-15 m/s causing both erosion and corrosion. There is nosolution today, but MAXTHAL shows promising results in tests with liquid lead of lowvelocity. There are also other issues unsolved, such as irradiation damage onstructural materials, thus more research is needed.Economic and political aspects were not covered in this study. This thesis work wasperformed at Vattenfall Research and Development AB