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Materials for gas turbine service
456
CURRENT TOPICS.
IJ. V. I.
ber (air-compressor tank) with a capacity of about 4.7 cubic feet. It is provided with an inlet valve for solvent and air, a pressure gauge, a needle valve, and a safety valve. Setting up and operating the apparatus is comparatively simple. The gasometer is first brought under reduced pressure by evacuating it. Then a weighed amount of the solvent whose vapor is to be tested is placed in a small flask and attached to the inlet valve. The latter is opened, and the inrushing air passes just above the surface of the solvent. By the time the chamber has reached atmospheric pressure, all the solvent has been swept in. Compressed air from a high-pressure cylinder is then admitted into the gasometer, where it ,nixes with the solvent vapor. When the desired amount of air has been let in, as registered by.the gauge, the supply is shut off. A simple calculation then tells just what concentration of vapor and air exists in terms of parts per million. The maximum operating pressure of the gasometer is 150 pounds. Opening the needle valve releases a stream of vapor-laden air, which is sufficient for a long series of calibrations. By starting off with a heavy concentration of solvent vapor, alternately calibrating instruments, and then admitting more air to dilute the residual moisture, it is easy to obtain a series of different known concentrations. Only compressed air which is pure is used in the gasometer, and the bureau's laboratory personnel keeps close check on the manner in which it is supplied. This method of using compressed air has saved the bureau many hours of tedious work and has played an important role in assuring adequate health and safety factors in the Detroit workers' environment. R. H. (). Materials for Gas Turbine Service.--Great strides have been made in the development of suitable materials for gas turbine service within a comparatively limited time. Selection of promising materials has been based on creep and rupture test results. Development of materials in use requires a knowledge of all properties of each material and extensive laboratory testing, including behavior under vibration or stress or temperature variation, heat shock, notch sensitivity. corrosion and erosion by hot gases, ductility and stability. One difficulty which required a vast amount of testing to destruction was obtaining satisfactory large forgings of austenitic materials. This problem was best solved by the development of the so-called "composite" wheel. This consists of a central or hub and disk portion of ferritic low-temperature steel and an outer or rim portion of high-temperature austenitic material solidly bonded together by a suitably controlled weld, using austenitic weld rod. This design has an additional advantage, in that the hub forging can include the shaft extension, thus eliminating the necessity of welding on a shaft extension. Despite the fact that much progress already has been made, extensive additional data are needed to develop new materials and to understand the laws governing high temperature material performance. A great deal must be done, too, to develop controls needed to ensure that materials always will possess the most desirable properties. R. H. O.
CURRENT TOPICS.
IJ. V. I.
ber (air-compressor tank) with a capacity of about 4.7 cubic feet. It is provided with an inlet valve for solvent and air, a pressure gauge, a needle valve, and a safety valve. Setting up and operating the apparatus is comparatively simple. The gasometer is first brought under reduced pressure by evacuating it. Then a weighed amount of the solvent whose vapor is to be tested is placed in a small flask and attached to the inlet valve. The latter is opened, and the inrushing air passes just above the surface of the solvent. By the time the chamber has reached atmospheric pressure, all the solvent has been swept in. Compressed air from a high-pressure cylinder is then admitted into the gasometer, where it ,nixes with the solvent vapor. When the desired amount of air has been let in, as registered by.the gauge, the supply is shut off. A simple calculation then tells just what concentration of vapor and air exists in terms of parts per million. The maximum operating pressure of the gasometer is 150 pounds. Opening the needle valve releases a stream of vapor-laden air, which is sufficient for a long series of calibrations. By starting off with a heavy concentration of solvent vapor, alternately calibrating instruments, and then admitting more air to dilute the residual moisture, it is easy to obtain a series of different known concentrations. Only compressed air which is pure is used in the gasometer, and the bureau's laboratory personnel keeps close check on the manner in which it is supplied. This method of using compressed air has saved the bureau many hours of tedious work and has played an important role in assuring adequate health and safety factors in the Detroit workers' environment. R. H. (). Materials for Gas Turbine Service.--Great strides have been made in the development of suitable materials for gas turbine service within a comparatively limited time. Selection of promising materials has been based on creep and rupture test results. Development of materials in use requires a knowledge of all properties of each material and extensive laboratory testing, including behavior under vibration or stress or temperature variation, heat shock, notch sensitivity. corrosion and erosion by hot gases, ductility and stability. One difficulty which required a vast amount of testing to destruction was obtaining satisfactory large forgings of austenitic materials. This problem was best solved by the development of the so-called "composite" wheel. This consists of a central or hub and disk portion of ferritic low-temperature steel and an outer or rim portion of high-temperature austenitic material solidly bonded together by a suitably controlled weld, using austenitic weld rod. This design has an additional advantage, in that the hub forging can include the shaft extension, thus eliminating the necessity of welding on a shaft extension. Despite the fact that much progress already has been made, extensive additional data are needed to develop new materials and to understand the laws governing high temperature material performance. A great deal must be done, too, to develop controls needed to ensure that materials always will possess the most desirable properties. R. H. O.