Fig. 2: RCF measurement by eddy current
and thus a conservative approach have been considered for the consideration. Ultimately, the metal removal rates, in combination with natural rail wear on both the High Rail and the Low Rail define the service life of the rails.
Life Cycle Cost Assessment
Fig. 3: Measurement of longitudinal profile of R260 and 400UHC® HSH® (R400HT) 1 m next to the weld
Appraisal of results
Corrugation and RCF defects (Head Checks) represent two key drivers for rail grinding or milling. While corrugation is not only one of the most important sources of railway noise, it is the structure-borne vibrations that arise due to corrugation, which ultimately lead to accelerated degradation of other superstructure components. Head Checks, a periodical crack pattern in the gauge corner area, represent a safety critical degradation mechanism that might lead to a multifractal rail break and thus need to be removed as a maintenance action. As former investigations have shown that RCF propagation in early stages tends to be nearly linear , the RCF measurement results suggest that at a hypothetical metal removal rate for rail grinding/milling of 0.5 mm is reached for 350HT HSH® after approximately 1.5 years, while the use of 400UHC® HSH® would lead to a grinding/milling interval of nearly three years. Therefore, not only the material removal rate can be reduced by using the 400 UIHC® HSH® steel grade, but also the maintenance intervals can be stretched. Railway operators benefit from the possibility to optimize the maintenance program with a high degree of flexibility, due to the robustness of the rail steel material. As for corrugation, a reduction by a factor of eight was reached after 2 years of service. The reduction of maintenance necessities becomes even more obvious in this case. However, for subsequent study, only Head Checking was taken into account
The Life Cycle Assessment was done by assuming stable annual traffic for the forthcoming years leading to an expected service live of more than 30 years for the 400 UHC® HSH® rails, with the aforementioned benefits in rail maintenance. By taking into account all costs related to rail implementation, rail grinding, or milling and the rail investment itself, the whole Life Cycle Costs were examined on the lowest equivalent annual costs, showing that the savings are in a range of 40 % as seen in Fig. 4. The significant reduction of Life Cycle Costs, by using 400UHC® HSH® rail steel, based on the conservative assumption of not taking into account the big advantage in corrugation, leads to a very stable ranking of results. The ranking of the strategies remains stable against major parameter changes e.g. traffic reduction of 50 %, or major increases in interest rates. Ultimately, the results suggest the use the rail steel 400 UHC® HSH® for the application of High and Low Rails in comparable curves. Due to the savings in maintenance costs for rail grinding, the investment in 400UHC® HSH® amortizes within the first 3 years.
Discovering the full organisatoric and economic potential
Having demonstrated how LCC in a curve were reduced by diminishing wear, along with RCF and corrugation by using 400UHC® HSH®, plus the fact that rail service live is stretched towards more than 30 years, major advantages become obvious: • T he application of 400UHC® HSH® in curves leads to a situation where Total Costs of Ownership of curves are converging to the costs of tangent tracks, where usually standard carbon rails are being used. • The maintenance regimes in these regions are also approximating the maintenance regimes of less stressed areas, which makes maintenance planning easier, by leading to longer sections with similar maintenance needs. These positive effects, observed in Vienna, demonstrate how stateof-the-art technology can be used to reduce costs and facilitate maintenance.  L . Prettner: How rail degradation influences the public perception, availability and profitability of Metro Systems, tdh rail magazine 67, 2018.  R . Heyder: Empirical studies of head check propagation and wear development, ZEVrail 137, 2013
Fig. 4: LCC assessment on basis of the measurements from underground line U6
The Official Magazine of the Asian Railway Operators Association and Rail Solutions Asia 2019