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This paper deals with life prediction by observation and simulation of short fatigue cracks in cyclically loaded smooth and notched specimens made of 0.15 wt-% carbon steel SAE1017. The measured crack behaviour was simulated in a microstructural environment. Reference tests under constant amplitude loading allowed to determine model parameters and hence a reasonable life prediction by simulation resulted even for service loading. Short crack behaviour was a measurable property for damage also to compare smooth and notched specimens.
In geothermal power plants materials e.g. pumps are exposed to extremely corrosive thermal water. This results in corrosion fatigue and so inevitably the reduction of the lifetime of these components. Also in the field of the carbon dioxide storage technology (carbon capture and storage CCS) components are exposed to a corrosive environment and mechanical stress. In order to gain knowledge upon the corrosion fatigue strength of materials a corrosion chamber for "in situ" conditions was designed and successfully applied.Two different steels X46Cr13 and X5CrNiCuNb16-4 have been tested and their corrosion fatigue behavior was compared. To simulate the frequency of operating pumps (30 – 40 Hz) a resonant testing machine was used. In addition technical CO2 was introduced into the closed system at a rate close to 9 L/h to keep stable environmental conditions. The samples have a surface roughness of Rz = 4 to simulate technical machined surfaces. The calculated tensile strength of X46Cr13 with soft annealed microstructure (coagulated cementite in ferrite-perlite matrix) is about 680 MPa and the yield strength is about 345 MPa. The tensile strength of X5CrNiCuNb16-4 is about 1078 MPa and the yield strength about 928 MPa. Testing parameters are: corrosion media: saline aquifer water (Stuttgart Aquifer) temperature of the brine at 60 °C and load ratio of R=-1. For X46Cr13 a stress amplitude between 160 MPa to 270 MPa and for X5CrNiCuNb16-4 a stress amplitude between 150 to 500 was chosen. Cycles until crack initiation differ strongly and were found to start at 5 x 104 up to 12.5 x 106 cycles.X46Cr13 has reached a maximum number of cycles (12.5 x 106) at a stress amplitude of 173 MPa. X5CrNiCuNb16-4 has reached the maximum number of cycles (10 x 106) at a stress amplitude of 150 MPa. The range of scatter for X5CrNiCuNb16-4 is very high (1:34) in comparison the range of scatter for X46Cr13 (1:3.5).
The lifetime reduction of cyclically loaded AISI 420C (X46Cr13, 1.4034) constantly exposed to highly corrosive CO2-saturated hot thermal water is demonstrated in in situ-laboratory experiments (60 °C, brine: Stuttgart Aquifer, flowing CO2: 30 L/h). SN plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion and corrosion fatigue behavior. Maximum number of cycles (here 12.5 × 106 cycles to failure) is reached at σa = 173 MPa. Hydroxide and siderite layers were found on pits and crack surfaces. No typical fatigue limit exists and pit corrosion prior to crack initiation may be identified as failure cause.
In corrosive environments such as CCS bore holes or geothermal power plants the materials loaded cyclically are also exposed constantly to the highly corrosive hot thermal water. The lifetime reduction of (X46Cr13, AISI 420C) is demonstrated in in-situ-laboratory experiments (T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 Nl/h, CO2). S-N plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion fatigue behavior. Maximum number of cycles (here 12.5 x 106 cycles to failure) is reached at σa =173 MPa. No typical fatigue strength exists and passive corrosion fatigue is most likely failure cause.
In geothermal power plants the materials used in pumps are loaded cyclically and
exposed constantly to the highly corrosive hot thermal water. The lifetime reduction
of AISI 420C (X46Cr13, 1.4034) is demonstrated in in-situ-laboratory experiments
(T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 l/h, CO2). S-N plots,
micrographic-, phase-, fractographic- and surface analysis were applied to obtain
sustainable information on the corrosion fatigue behavior. Maximum number of
cycles (here 12.5 x 106 cycles to failure) is reached at σa =173 MPa. No typical
fatigue strength exists and passive corrosion fatigue may be identified as failure
cause.
Design of a high pressure system for in-situ tests on the corrosion fatigue of metallic materials
(2014)
In geothermal power plants pumps are exposed to corrosive and oscillating loads. This leads to corrosion fatigue and reduces the lifetime of certain components. Usually underwater power pumps are placed inside the borehole. In this case an installation depth of 600 to 800 meters below ground level is typical. In these depths an additional load due to high pressure and high temperature is introduced which is based on geothermal brine. Therefore the material which is used for the pump is steel.For fatigue testing at loads existing in deep geological layers an appropriate system for fatigue tests under in-situ conditions was set up. The requirements of the design are: temperature of the corrosion medium of 200 °C pressure of 200 bars and the complete immersion of the specimen in flowing corrosion medium containing mixtures of corrosive gasses during the entire test period.The test system has three main components the corrosion chamber the heating module and the reservoir. It is important that the corrosion chamber is only fixed onto the specimen which allows for highest flexibility of the test system operational in many different test machines. The heating module heats the corrosion medium up to 200 °C. The reservoir make sure that the volume of the corrosion medium satisfies requirements of the DIN 50905 Part 1 is conformed providing minimum required corrosive medium of 10 ml/cm² in relation to the sample surface.This innovative fatigue test system aims at performing in- situ fatigue corrosion tests simultaneously at high pressure and high temperature in liquid and gaseous corrosive environment. Results from the tests will allow determining the fatigue life of several materials influenced by pressure and temperature under corrosive conditions.
On October 24th 1950 the 'Freedom Bell' rung for the first time in the tower of the former West Berlin town hall. One year after the Berlin blockade and at a first climax of the 'Cold War', the 'American National Committee for a Free Europe' donated the bell to the city of West Berlin. The bronze bell has a weight of about 10 tons. Its clapper has a length of 2.40 m and a weight of nearly 1 ton. In 1966 the hanging of the clapper and in 1979 the clapper of the bell broke down. Both failures were found to be caused by fatigue fracture. In 1974, a crack in the bell body was detected. After years of periodic monitoring using non-destructive testing, the crack was closed in 2001.
The development of procedures to calculate the service life of railway rails requires test results which describe the damage of rails thus affording their validation. Within the DEUFRAKO integrated project NOVUM, ten rail specimens were tested under constant and variable amplitude loads to investigate the propagation of lateral cracks and to ascertain the service life. The test conditions were based on real rail loading and were used in the 3-point-bending test frame under alternating stress. An eccentric notch was applied as pre-arranged damage in the 60 E1 (260) rail specimens. The notched rails showed a similar behaviour like rails with strong head checks damaged by rolling contact fatigue.
In the field of water pipelines, geothermal energy production as well as carbon capture and storage technology (CCS) materials have to provide a high resistance to corrosion and mechanical stress. The combination of cyclic load and corrosive aqueous environment leads to corrosion fatigue of pipes and components (e.g. pumps) and thus inevitably to the reduction of the lifetime of these components. To estimate the reliability of components from adjusted in-situ-laboratory experiments a corrosion chamber was designed and tested with CO2 saturated corrosive aqueous media flowing at a steady rate. Unique feature of this special chamber is its installation directly onto the sample and thus providing flexible usability in almost every testing machine. This allows simultaneous mechanical loading of the sample, operation at temperatures up to 100 °C and exposure to fluid flow of corrosive liquids and gases. The lifetime reduction of AISI 420C (X46Cr13, 1.4034) is demonstrated at T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 l/h, CO2. S-N plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion fatigue behavior. Maximum number of cycles (here 12.5 x 106 cycles to failure) is reached at σa =173 MPa. No typical fatigue strength exists and passive corrosion fatigue may be identified as failure cause.