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Eingeladener Vortrag
- nein (985)
Different types of lasers are used nowadays for a number of technological Solutions, Modem high power solid-state lasers with high brightness of Radiation like Fiber or disc lasers find ever more applications in welding technology. Apart from the replacement of the CC>2-iasers traditionaHy used fcr these purposes, they provide new technological possibilities of metal treatment, such as using industrial robots and remote welding with high power laser radiation. The possibility of flexible optical fiber delivery of the radiation to any point gives a great technological advantage and permits welding processes to be realized with complicated weld seam geomelries and different positions using a minimum of additional fixtures. The short wavelength of the high power solid state lasers (1.07 ’m) causes another advantage. The coefflcient of inverse 170
Bremsstrahlung absorption from free electrons in plasma for such radiation is about 100 times lower than for the COi-iaser radiation. Owing to this fact, using the solid state lasers allows it to avoid a negative influence of the welding plume.
However, a short wavelength can lead to another kind of laser Radiation attenuation, which is connected with the formation of a cloud consisting of small metal particles that absorb and scatter laser radiation. This cloud arises due to the condensation of hot metal vapor by flying out from the deep Penetration channel and broadening in relatively cold atmosphere over the metal Surface.
Some theoretical and experimental approaches were made in advance in Order to estimate the influence of the Condensed particles on laser radiation and welding quality.
In this paper a systematic study including the determination of the Cloud size and its dynamical characteristics is presented. The results were obtained within the scope of the first stage of the metal vapor condensation process Investigation during welding with high power fiber lasers.
Coda wave interferometry is a recent analysis method now widely used in seismology. It uses the increased sensitivity of multiply scattered elastic waves with long travel-times for monitoring weak changes in a medium. While its application for structural monitoring has been shown to work under laboratory conditions, the usability on a real structure with known material changes had yet to be proven. This article presents experiments on a concrete bridge during construction. The results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions. Theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations.
Dealing with first corrosion screening experiments to predict the reliability and safety of Germanys first Carbon Capture and Storage site in the northern Bassin of Germany, northwest of the Capital Berlin, laboratory experiments have been established to simulate the particular conditions at T=60 °C, highly saline aquifer water similar to 'Stuttgart Aquifer', but only at ambient pressure. With mounting 2 independent full 2-grade titanium autoclave systems (running up to 250 bar and 300 °C) pressures up to p=100 bar are possible. In 2010 a specific corrosion chamber of 2-grade titanium working up to 100 °C, flowing aqui fer water with different gas mixtures was designed to fit to a high cycle fatigue testing machine. Long term fatigue experiments simulating fatigue crack growth under corrosive environments will soon start. These experiments may not only help engineering a CCS site, but results can be used to improve the maintenance of geothermal energy production sites, especially moved parts such as pumps and shafts.
The CCS technique involves the compression of emission gasses in deep geological layers. To guarantee the safety of the site, CO2-corrosion of the injection pipe steels has to be given special attention when engineering CCS-sites. To get to know the corrosion behaviour samples of the heat treated steel 1.72252CrMo4, used for casing, and the stainless injection-pipe steel 1.4034 X46Cr13 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h - 8000 h in a CC 2-saturated synthetic aquifer environment similar to possible geological on-shore CCS-sites in the northern German Basin. The isothermal corrosion behaviour obtained by mass gain of the steels in the gas phase, the liquid phase and the intermediate phase gives surface corrosion rates around 0.1 to 0.8 mm/year at ambient pressure and much lower about 0.02 to 0.2 mm/year at 100 bar where the CO 2 is in its supercritical state. Severe pit corrosion with pit heights around 4.5 mm are only located on the 42CrMo4 steel. Main phase of the continuous complicated multi-layered carbonate/oxide structure is siderite FeCO 3 in both types of steel.