Failure Analysis of Switch Rails and Crossings Towards Maintenance Improvement: A Case Study of Addis Ababa Light Rail Transit
No Thumbnail Available
Date
2024
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Railway systems are such a complex transportation systems that consists several
components like rails, switches, crossings, check rails, turnout carriers, and some
other components. Maintenance of railway “switch and crossing” (S&C) systems is
critical for effective and safe train operations. The material degradation and geometry
optimization of switches and crossings should be considered for an efficient operation
of railway system. The failures of railway tracks are an unavoidable phenomenon that
affects the operation intensively. AALRTS rail material is 50 Kg/m U71Mn and the
frog is Hadfield steel. Previously different failure assessment and investigation
researches have been carried out, however, failure investigation techniques need to be
updated frequently and assessed because the problem still exists. Markov chain model
was implemented for statistical analysis of critical failures and the output results are
“Mean Time To Failure” for both critical and disastrous failures. Based on the results
it is possible to recommend that increasing the number o f “Ultrasonic Inspection
Cars” test from 3 to 5 or increasing the test interval from 122 days to 73 days per year
will minimize “Mean Time To Failure” from 3.1 years to 1.6 years. The mean time
to failure results can be an input for a strategic track maintenance planning. “Failure
mode, effects, and criticality analysis” (FMECA) were implemented to identify the
most critical failure mode with higher risk. The welded rail specimen`s quality,
hardness, and microstructural features were evaluated at different cooling rates
experimentally. To identify and assess the microstructure feature and hardness of rail
welding through different cooling rates three major NDT tests have been employed.
Increasing the number of tests of inspection or the inspection interval will minimize
the mean time to failure. Generally, all the non-destructive test results demonstrate
that there is a noticeable defect on the welded rail cooled at 6°C/s. Comparatively
fewer defects were observed on the welded rail cooled at 3°C/s; while acceptable
defects were manifested on the one cooled at 2°C/s. The minimum cooling rate can be
achieved through both preheating and post-heating process.
From the switch panel, “Failure mode, effects, and criticality analysis” (FMECA)
results “gauge corner spalling” failure mode was with the highest risk priority number
so that its improvement has a great influence on the maintenance efficiency.Additionally, from the detail results of failure mode, effects, and criticality analysis
(FMECA) of turnouts; failure modes under high risk category need special attention
during maintenance planning and need improvement of rectification techniques. From
the results of the analysis six failure modes have been laid under high risk categories
whereas two failure modes have been laid under moderate risk categories and four
failure modes have been laid under low risk categories. As a conclusion cooling of
rail welding`s at 2°C/s cooling rate will give the material good micro-structural
feature and better weld quality relatively. This minimum cooling rate 2°C/s achieved
by uniform and optimum preheating and post-heating temperatures. Finally, the
researcher recommend a controlled cooling rate for welding quality improvement and
maintenance efficiency increment.
Description
Keywords
Failure assessment, damages on turnouts, failure`s severity, failure modes, sensitivity analysis, Switch rail and crossings.