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Shortly after midnight on 15th November 1992, a severe train crash was caused by the break off of a buffer from a tool and gear wagon of a freight train. The buffer fell between the rails, tumbled, and then lifted one axle of a following freight wagon off the rails. Several freight wagons derailed in the station of Northeim, Germany, blocking the adjacent track. A night train travelling on that blocked track was already too close (only 180 m) to stop, despite emergency braking initiated immediately and automatically by the track signalling system. When the night train crashed into the freight wagons, some of its coaches were heavily damaged. Eleven people were killed, and 51 injured, some of them seriously.
The task for failure analysts was to find out why the buffer broke off from the front frame of the tool and gear wagon. Therefore, the material of the attachment, the front frame, and the welds were tested. Chemical composition, hardness, and microstructure were allowable. The welds showed imperfections which were determined not to be causal. The fracture surfaces had graded corrosion which again was not causal and beach marks that depicted fatigue cracks before final fracture.
The cause for the break off was the fact that the front frame had been repaired at this same buffer attachment some years before and that the repair patch used was thinner than the original front frame profile.
Additionally, the force characteristics of the buffer showed reduced stroke but increased forces which was due to several friction springs that had been broken for a long time. The buffer forces in service were assessed from standards, literature, and the deformations of the attachment. The in-service stresses at the welds were estimated using FEM analysis. High cyclic stresses at the welds resulted in fatigue cracking and finally break off of the attachment with the buffer.
The process chain for Carbon Capture and Sequestration (CCS) includes tubing for injection of CO2 into saline aquifers. The compressed CO2 is likely to contain specific impurities; small concentrations of SO2 and NO2 in combination with oxygen and humidity are most harmful. In addition, CO2 saturated brine is supposed to rise in the well when the injection process is interrupted. The material selection has to ensure that neither CO2 nor brine or a combination of both will leak out of the inner tubing. In this comprehensive paper the investigated materials range from low-alloy steels and 13% Cr steels up to high-alloy materials. Electrochemical tests as well as long term exposure tests were performed in CO2, in brine and combination of both; pressure was up to 100 bar, temperature up to 60 °C. Whereas the CO2 stream itself can be handled using low alloy steels, combinations of CO2 and brine require more resistant materials to control the strong tendency to pitting corrosion. The corrosion behavior of heat-treated steels depends on factors such as microstructure and carbon content. For different sections of the injection tube, appropriate materials should be used to guarantee safety and consider cost effectiveness.
Condensates from the gas stream in simulated CO2 transport pipelines have been identified during the experiments in the laboratory. Because of their acidic origin the corrosion resistance of pipeline steels used for CCS (carbon capture and storage) technology might be limited. Over the last years it has become clear that the amount of water and acid building constituents in the CO2 stream has to be controlled very well. In this work, condensates formed in experiments using gaseous CO2 containing high amounts of water, NO2 and SO2 were analyzed, replicated, and used for extensive electrochemical experiments. These highly acidic condensates were enriched with CO2 and then applied to characteristic steels planned to use in the CCS transport chain. Even high alloy steels are susceptible to localized corrosion under these conditions. The results implicate that condensation of aggressive acid droplets has to be avoided or the locations where condensation takes place have to be controlled extensively.