43
Chapter 3
Safe Rail Transport via
Nondestructive Testing
Inspection of Rails and
Communications-Based
Train Control Systems
Vassilios Kappatos, Tat-Hean Gan,
andDimitrisStamatelos
Contents
3.1 Introduction .............................................................................................. 44
3.2 Overview of CBTC’s Capacity ...................................................................45
3.3 Rail and Fastening Parts Infrastructure ..................................................... 46
3.3.1 Superstructure Subsection.............................................................. 46
3.3.2 Rail Overview ................................................................................ 46
3.3.2.1 Defects in Rails ................................................................47
3.3.3 Fastening Parts Overview ...............................................................49
3.3.4 Critical Place on Rail Network .......................................................49
3.4 Rail and Fastening Parts Inspection ...........................................................50
3.4.1 Manual and Automated Visual Rail Inspection ..............................51
3.4.2 Liquid Penetrant Rail Inspection ....................................................52
3.4.3 Ultrasonic Rail Inspection ..............................................................52
3.4.3.1 Conventional Ultrasonic Rail Inspection ..........................53
44 ◾ Advances in Communications-Based Train Control Systems
3.1 Introduction
Trains constitute one of the most popular and ecient means of passenger and
freight transport all over the world. e rapid and continuous increase in train
trac, train speed, and tonnage carried on the rail network has posed the challenge
of ensuring that rail travel remains a safe, attractive, and on-time mode of transport
for people and goods to public authorities and railway companies.
Failures and unavailability of railway infrastructures
*
and rail operations can
have catastrophic consequences. One of the most common precursors to cata-
strophic accidents on the railway is signal passed at danger
†
(SPAD) [1]. A high
number of SPAD incidents happen each year, even though the majority of them are
highly unlikely to result in a serious accident, due to the high probability of instant
braking and/or the low speeds observed. However, a safety violation in Chatsworth,
California, in September 2008, resulted in a collision between a freight train and
a commuter train [2], causing the death of 26 people and more than 135 people
injured. Another accident occurred in Macadona, Texas, in June 2004, when a train
passed a stop signal without authority to do so, which resulted in three deaths and
30 people injured [3].
Apart from the SPAD accidents, many accidents were caused by the cata-
strophic failure of rail components, such as in Hateld, Hertfordshire, in October
2000, that led to the loss of 4 lives and 70 people injured [4] and in Minot, North
Dakota, in January 2002, when a freight train derailed, spilling gas and hazardous
materials, killing at least one person, and injuring around a hundred more. e
National Transportation Safety Board determines that the probable cause of the
*
e term “railway infrastructure” covers all assets used for train operations, except rolling stocks.
A denition of railway infrastructure is given by the European Community Regulation 2598/1970
and comprises routes, tracks, and eld installations necessary for the safe circulation of trains.
†
A SPAD occurs when a train passes a stop signal without authority to do so.
3.4.3.2 Laser Ultrasonic Rail Inspection ....................................... 53
3.4.3.3 Phased Array Ultrasonic Rail Inspection ..........................54
3.4.3.4 Rail Inspection Using Long-Range Ultrasonics
(Guided Waves) ................................................................54
3.4.4 Magnetic Flux Leakage Rail Inspection .......................................... 55
3.4.5 Eddy Current Rail Inspection .........................................................56
3.4.6 Alternating Current Field Measurement
Rail Inspection ...............................................................................57
3.4.7 Rail Inspection Using Electromagnetic Transducers .......................57
3.5 Comparison of NDT Techniques ............................................................... 57
References ...........................................................................................................62
Safe Rail Transport via Nondestructive Testing Inspection ◾ 45
train derailment was the misidentication and nonreplacement of the cracked joint
bars [5].
Almost all the accidents and the associated casualties caused by SPAD and fail-
ure of rail components could have been at least minimized or altogether prevented,
as long as train protection (TP) equipment had been installed and operated, and
through careful nondestructive testing (NDT) inspection and appropriately sched-
uled maintenance of rails, respectively. Both TP and NDT of rails are signicant,
safety-critical applications, which show very demanding requirements in terms of
availability, continuity, and integrity. In order to fulll these high-performance
demands, it is essential that both terms are understood fully.
is chapter mainly studies the NDT techniques that can be employed to
inspect rails and fastening parts as well as relevant research and development work
in this eld. As the NDT techniques signicantly depend on the nature of defects,
a discussion about the defects that emerge on the rail infrastructure takes place.
Finally, in Section 3.2, an overview of the capacity of the recent TP methods
mainly based on the communications-based train control (CBTC) is carried out
for a complete overview of all measures (NDT, TP) that can be used to avoid any
potential and serious rail accidents.
3.2 Overview of CBTC’s Capacity
Over the long term, it was easier to develop devices to protect against signal errors
than driver errors, but by the late 1980s electronics had developed to the point at
which it was possible to protect against driver errors by installing systems that contin-
uously supervise the movement of trains and automatically apply the brakes if a train
is going too fast for current track and signaling conditions. TP is equipment tted to
trains and the track that can reduce risks from SPADs and overspeeding. ere are
many dierent ways of preventing SPADs or reducing their eects, including dier-
ent types of automatic TP (ATP) in the United Kingdom and the European Union,
and positive train control (PTC) in the United States. Generally, ATP refers to either
of two implementations of a TP system installed in some trains in order to help pre-
vent collisions through a driver’s failure to observe a signal or speed restriction.
Railway signaling systems are essentially used to prevent trains from colliding.
One of the railway signaling systems that makes use of the telecommunica-
tions between the train and the track equipment for the trac management and
infrastructure control is the CBTC
*
. CBTC has been under development since
the mid-1980s [6–8]; however, wide-scale adoption has not occurred because of
*
As dened in the IEEE 1474 standard (IEEE, 1999), a CBTC system is a “continuous, automatic
train control system utilizing high-resolution train location determination, independent of track
circuits; continuous, high-capacity, bidirectional train-to-wayside data communications; and
trainborne and wayside processors capable of implementing ATP functions, as well as optional
automatic train operation (ATO) and automatic train supervision (ATS) functions.”
46 ◾ Advances in Communications-Based Train Control Systems
technical, practical, economic, and institutional barriers [9]. Recent regulations
and legislation have altered the situation [10] and have mandated PTC’s imple-
mentation on a large portion of the main lines by 2015.
A number of studies have previously investigated the impact of CBTC on the
capacity. Lee et al. determined that moving blocks could increase the capacity of the
Korean high-speed railway [11]. Another study quantied the capacity benets of
the European Train Control System, Europe’s version of CBTC [12]. In the United
States, Smith et al. studied the potential benets of Burlington Northern’s Advanced
Railroad Electronics System and other possible CBTC systems [13–16]. ey calcu-
lated how the more ecient meet–pass planning and the increased dispatching eec-
tiveness possible with CBTC will aect the capacity. Martland and Smith calculated
the potential terminal eciency improvements resulting from the estimated increases
in reliability oered by CBTC [17]. Many authors have claimed that a CBTC system
with moving blocks will increase capacity [7,13–15,18]. CBTC makes the train, sig-
nal, and trac control systems more “intelligent” [19], allowing the railroad to better
plan and control train movements, increasing railroad eciency and capacity.
3.3 Rail and Fastening Parts Infrastructure
3.3.1 Superstructure Subsection
Maintenance of rail infrastructure can refer to the following components: mainte-
nance of track (structured into superstructure and subgrade subsections), bridges and
tunnels, electrication equipment, signaling and communication equipment, rail trac,
and so on. e superstructure is subject to periodical maintenance and replacement.
A survey conducted among maintenance agencies [20] revealed that most mainte-
nance activities of superstructure subsection are concentrated in rail and all fasten-
ing parts maintenance.
e elements to be considered in the superstructure (Figure3.1) are mainly
rail, which supports and guides the train wheels; sleepers and all fastening parts,
which distribute the loads applied to the rails and x rails to railroad ties; ballast,
which usually consists of crushed stone—and gravel only in exceptional cases—
and should ensure the damping of most of the train vibrations, adequate load distri-
bution, and fast drainage of rainwater; and sub-ballast, which consists of gravel and
sand. is protects the upper layer of the subgrade from the penetration of ballast
stones, whereas at the same time it contributes to distributing further external loads
and ensuring the quick drainage of rainwater.
3.3.2 Rail Overview
Rails are longitudinal steel members that accommodate wheel loads and distrib-
ute these loads over the sleepers or supports, guiding the train wheels evenly and
Safe Rail Transport via Nondestructive Testing Inspection ◾ 47
continuously [21]. ere is a range of rail cross sections, materials, weights, and
head proles used worldwide. Mainly, rails are made from high steel, which has led
to a signicant improvement in rail fatigue performance and a considerable reduc-
tion in residual stress development [22]. Many standards are used for rail proles,
which are classied into the International Union of Railways, the American Society
of Civil Engineers, the American Railway Engineering Association, and the British
Standards. Other proles are used in the Netherlands, Denmark, Germany, India,
China, South Africa (SAR), and so on. In Europe, the maximum static axle load
ranges about 21–25 ts; in the United States, it normally reaches almost 30 ts and in
Australia about 37 ts has been reported on iron-ore vehicles. All these axle loads are
nominal values, assuming that vehicles are uniformly loaded [23].
3.3.2.1 Defects in Rails
In service, rails can suer from two types of defects: noncritical and critical.
Noncritical defects do not aect the structural integrity of the rail and/or the
safety of the trains operating over the defect; however, critical defects aect these.
Typically, the parts of a rail where defects can usually be found are head, web, foot,
switchblades, welds, and bolt holes. Although the majority of defects are located in
the head, they can also be found in the web and foot. Figure 3.2 demonstrates the
propagation of a single crack in the rail head.
Rail defects have been classied in many ways. Depending on their initiation,
defects can be divided into three wide groups [24] (Figure 3.3):
1. Cracks caused by manufacturing defects [25]. Rail manufacturing defects are
generally a result of nonmetallic origin or wrong local mixings of the rail
steel components that, under operative loads, generate local concentration of
stresses, which trigger the rail failure process [26].
Sup
erstructure
Sleeper
Rail
Ballast
Sub-ballast
Figure3.1 Superstructure subsection.
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