Reliability Analysis of Switches and
Crossings – A Case Study in
Swedish Railway
Behzad Ghodrati, Alireza Ahmadi, Diego Galar
Division of
Division of Operation and Maintenance Engineering
Luleå University of Technology, Sweden
and
Maintenance
1
Introduction
Railway complexity:


Mix of components with different age
Working together
Minimize
maintenance
time
Division of
and
Maintenance
Higher
Increase
 Maintenance be performed
near capacity limits
utilization
traffic
 Time between asset
renewals be long enough
of capacity
volume
Minimize
unplanned
interruption
2
Introduction
The key goal is to achieve availability target
cost effectively.
Availability
Reliability
Maintainability
Supportability
To conduct reliability analysis:
Division of
and
Maintenance

Detail failure and maintenance recorded data
 Detail maintenance action done
 Mission profile: duty cycle and environmental
characteristics
3
RAMS
Reliability: Ability of an item to perform a required
function under given conditions for a given time
interval.
R(t )  et
RAMS
Availability:
Ability of anmaintainability
item to be in a state
to safety)
(reliability,
availability,
and
Division of
perform a required function under given conditions
at a given instant of time or during a given time
interval, assuming that the required external
resources are provided.
and
Maintenance
A
Total time   Times of repair
Total time
4
Switches
A railroad switch, turnout or set of points is a
mechanical installation enabling railway trains to be
guided from one track to another at a railway junction.
Name of switche in Swedish railway system: A-B-C-D (e.g.
EV – SJ50 – 11 – 1:9),
A: type of switch (single, double)Check rail
B: type of railpanel
Division of
and
Maintenance
C: radius or length of switch blade
D: type of angle
5
Switch and Crossing Elements
Division of
and
Maintenance














Ballast
Check rail
Cross over panel
Crossing
Fasteners
Heating system
Locking device
Rail
Rail joint (mostly protected rail joint)
Sleeper (bearer)
Snow protection
Switch blade
Switch blade position detector
Switch device (motor, gearbox,
coupling, bars, etc.)
6
Sweden railway network
BODEN
ÅNGE
GÄVLE
HALLSBERG
STOCKHOLM
Division of
NORRKÖPING
and
Maintenance
GÖTEBORG
7
MALMÖ
Data collection and evolution
Raw Data
43528 failures
Switches with
numbers inferior to
50 was eliminated
Number of registered failures
Jan. 2005 – Dec. 2009
Raw data without unnecessary types of turnouts
42221 failures
Installation
date known
Turnouts
known
Division of
and
Maintenance
- Changed between
05/09:
-in BESSY (1452
failures)
-not in BESSY
- Not changed
-installation date
”0" (2004 failures)
-the rest (25006
failures)
Age and location
of turnouts
Installation
date unknown
Turnouts
unkown
- In BESSY (30 failures)
- Not in BESSY
Turnouts
known
- Changed between
05/09:
-in BESSY (31
failures)
-not in BESSY
- Not changed
-installation date
”0" (176 failures)
-the rest (977
failures)
- #N/A
Turnouts
unkwown
- Unkwown (10477
failures)
29676
failures
8
Final available data
10477
failures
24%
68%
29676
failures
Division of
8%
Turnouts unkown
Data not found in the
different files
Data available for study
3375
failures
Take into account the 10 types of turnouts
generating most failures and 60 tracks of interest
and
Maintenance
16627 failures
9
Studied tracks and switches
9 (out of 60) focused tracks
Track
number
Division of
and
Maintenance
Type of track
124
Freight track
410
Commuter trians and some freight
414
Mixed passenger and freight
420
Mixed passenger and freight
512
Mixed passenger and freight
611
Mixed passenger and freight
811
Mixed passenger and freight
813
Mixed passenger and freight
912
Mixed passenger and freight
Tracks with more
failures with at least
10 individuals asset
names and at least 2
types of turnouts
10
10 types of turnouts
generating more failures
EV-SJ50-11-1:9
5301
EV-UIC60-760-1:15
4291
EV-SJ50-12-1:15
3224
DKV-SJ50-…
2997
EV-UIC60-300-1:9
2890
EV-UIC60-1200-1:18,5
EV-UIC60-1200-…
Division of
and
Maintenance
1745
Number of failures
1214
EV-UIC60-760-1:14
867
EV-SJ50-12-1:13
715
EV-SJ50-12-1:12
641
EV-SJ50-11-1:9
EV-SJ50-12-1:15
EV-SJ50-11
0
2000 4000 6000
EV-UIC60-1200-1:18,5
EV-SJ50-12
EV-UIC60-1200-1:18,5
EV-UIC60-300 BL33
EV-UIC60-300-1:9
EV-UIC60-760
EV-UIC60-760-1:14
EV-UIC60-1200
EV-UIC60-760-1:15
11
Data classification
Dividing into 2 seasons
COLD
from November to March
(5 months)
HOT
from April to October (7 months)
Proportion of failures by
season
45%
55%
Cold
Hot
Dividing into 2 types of tracks
Division of
and
Maintenance
nhsp
main track
ahsp
diverging track
12
Subsystems affected by
failures – Hot period
Switch blade position detector
2520
(blank)
2057
Switch device (motor, gearbox,…
1616
Switch blade
Division of
and
Maintenance
710
Heating system
120
Rail joint (mostly insulated rail joint)
109
Fasteners
98
Crossing
79
Locking device
62
Snow protection
47
Rail
31
Sleeper (bearer)
13
Ballast
10
Check rail
7
Cross over panel
3
0
Hot
500
1000
1500
2000
2500
3000
13
Subsystems affected by
failures – Cold period
(blank)
2765
Switch blade position detector
2521
Switch device (motor, gearbox,…
1474
Heating system
1194
Switch blade
624
Snow protection
Division of
and
Maintenance
105
Rail joint (mostly insulated rail joint)
80
Crossing
79
Fasteners
66
Locking device
57
Rail
36
Check rail
10
Ballast
8
Sleeper (bearer)
7
Cross over panel
4
0
Cold
500
1000 1500 2000 2500 3000
14
Comparison of subsystems with
more failures during the two
seasons
Switch blade position
detector
2520
2521
2057
(blank)
2765
Switch device (motor,
gearbox, coupling, bars, ...)
1616
1474
710
624
Switch blade
Division of
and
Maintenance
HOT
COLD
120
Heating system
1194
0
1000
2000
3000
15
Data analysis tool
RDAT (Reliability Data Analysis Tool) software was developed
by Alstom and the University of Bordeaux (France), and deal
with highly censored field data which wasn’t taken into
account properly with the already existing programs.
RDAT was used to estimate the reliability functions and failure
rates from field data
Four failure models have been implemented in RDAT:
exponential, Weibull, normal, and lognormal distributions.
To select the best model, a goodness-of-fit test is applied.
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and
Maintenance
The maintenance quality is considered by a parameter
denoted Rho:

ρ = 1 means that the maintenance quality is AGAN (the
maintenance operation is perfect).

ρ = 0 means that the maintenance quality is ABAO (the
mission can continue but leaves the item with a reliability
corresponding to the age accumulated so far).
16
RDAT software methodology
Work on
First Failure
Maintenance
effect analysis
POSSIBLE
No
Is Exponential best
Estimator?
Yes
Maintenance
effect analysis
NOT POSSIBLE
Kijima
Division of
and
Maintenance
Rho = 0
0 < Rho < 1
Rho = 1
Work on
ABAO
Work on
First Failure
Work on
AGAN
Work on
First Failure
Intrinsic Reliability Analysis
17
Data analysis – RDAT software output
Division of
and
Maintenance
70% of
cases ρ
=1
AGAN maintenance
30% of
cases, ρ
= 0,5-1
ABAO maintenance
Trafikverket (Swedish Railway Administration) maintenance
experts consulting:
ABAO model was considered
18
Data analysis – RDAT software output
 Instantaneous failure
rate
λ failure rate

β shape parameter
 
n
T
n
n
n  ln T   ln Ti
i 1
Division of
and
Maintenance
 Instantaneous Mean Time Between
Failures
19
RDAT implementation and results
Growth factor Beta as a function of types of turnout and season and type
of track
β < 1 → MTBF ↗

Division of
and
Maintenance


Maybe the maintenance has improved in these 5 years (Case of
infant mortality: many problems at the beginning)
The organisation learned how to deal with failures during 05/09
Other possible explanation:


For SJ50-11 switch point detectors taken out (less
failures)
Change of switch point detectors on the other types of
turnouts (from mechanical to electrical) > reduces
number of failures in Hot and Cold
20
RDAT implementation and results
Growth factor Beta as a function of types of turnout and season and type
of track
β > 1 → MTBF ↘
Division of
and
Maintenance

”Old equipment fails more” > Maintenance is not compensating
the age of the turnout
21
RDAT implementation and results
Comparison between hot/cold
 There are much more β < 1 during COLD season, better
maintenance? More effective maintenance during winter time?
 There are much more β > 1 during HOT season, worst
maintenance?
Is there any link with the number of failures avery year?
Division of
and
Maintenance
22
Comparison between hot/cold
There is no relationship
Division of
and
Maintenance
between the number of failures
every year and the improved or
not of the maintenance for
these years.
23
RDAT results
Values of λ and β for different types of turnouts for the 9 tracks
Division of
and
Maintenance
Example for tracks 124, 410 and 912 for main track and SJ50-11
24
RDAT results
Example for tracks 124, 410 and 912 for main track and SJ50-11
β ≈1
β ≥1
β ≤1
Division of
and
Maintenance
25
RDAT results
Instantaneous failure rate (SJ50-11 and nhspcold)
0.0004
Division of
and
Maintenance
Failure rate (λ)
0.00035
0.0003
0.00025
124
410
912
0.0002
0.00015
0.0001
0.00005
0
3
6
9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Months (from January 05 to December 09)
26
RDAT results
Instantaneous failure rate (SJ50-11 and nhsp-hot)
0.0004
Division of
and
Maintenance
Failure rate (λ)
0.00035
0.0003
0.00025
124
410
912
0.0002
0.00015
0.0001
0.00005
0
3
6
9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Months (from January 05 to December 09)
27
Availability
Turnouts are in serie in a track
Turnout
1
Turnout
2
Turnout
3
Turnout
4
Division of
and
Maintenance
28
Conclusion
 The RAMS analysis confirms the more failure in Cold season
than in Hot season
 For tracks 124, 410 and 912

Failure rate decreasing during Cold season

Failure rate almost constant during Hot season
 Track 512, which has the lowest availability, needs to be
focused for improvement
Division of
and
Maintenance
 The RDAT software is not taking into account this
parameter. However, it is possible to do a covariate analysis
including this factor.
 On the most important failure contributors, which are the
switch blade position detectors, switch devices, heating
system in the cold season, and switch blades
29
Division of
and
Maintenance
30