An Introduction to Rail - Network Rail engineering education (11 of 15)


Uploaded by networkrail on 27.03.2012

Transcript:
[train passing]
♪ background music ♪
(Narrator) At Network Rail we're responsible
for over 20,000 miles of track
and that means
over 40,000 miles of rail.
Rail has many advantages over roads.
It's self-steering and faster,
it's got a higher loading capacity
and, most of all, it's safer.
[train passing]
15 times safer than travelling by car.
And one of the main reasons
it's so safe is because
our maintenance teams and engineers
put a huge amount of work and care
into looking after it.
The type of material we choose
to make our standard rail from
is very important
and highly specified.
It's a 0.6% carbon steel
with other alloying additions
to increase its strength and hardness.
It's a high performance material
and as hard as a typical drill bit.
99% of our rail is made by Tata Steel
in their huge steelworks in Scunthorpe.
As a guide to the
scale of the operation
the building containing
the rail production line
is over a mile long.
The rail production process begins
with 7.5 meter long blocks of steel
called "blooms" weighing 6.5 tonnes.
These blooms are heated in a furnace
to 1,240 degrees centigrade
to make the steel behave plastically
and be capable of being shaped.
The red-hot blooms are cleaned
and de-scaled and then
moved through the production line.
Computer controlled machinery
squeezes, rolls and manipulates
the blooms into a new form.
In less than 10 minutes,
the original bloom has
a completely new cross-section profile
and has been transformed
from 7.5 meters
to just over 108 meters in length.
The rails are then pre-bent
whilst still hot to counter the bending
that occurs as they cool.
Once cooled, the rails
are straightened and trimmed
and then passed through a
complex computer controlled NDT process
to look at their profile, internal
and surface quality using UV, lasers,
ultrasonics and eddy currents.
The tests ensure that every rail
leaves the site free from defects.
At Network Rail we want
the longest rails
that we can practically deliver.
The fewer joins, the stronger the rail.
The longest rail that Tata Steel
currently supplies to us
is 108 meters long. So two rails
are flashback welded together
to produce a 216 meter string.
This is the practical limit
of what we can deliver to track.
Finally the finished rails are loaded
onto a delivery train.
The rails are flexible enough
to negotiate bends in the line
and make their journey direct
to the location where they're required.
The standard of rail
produced by Tata Steel is very high.
But even the best rails
won't last forever.
(Brian) My name is Brian Whitney.
I'm the Principal Track Engineer
for Network Rail.
Part of my job is to understand
how the degradation of rail occurs,
how quickly it happens,
where it happens
and how to mitigate against it.
There's four main types of degradation
we see with rail.
There's fatigue damage on the surface
and internally within the rail.
There is wear. Both on the head
and side wear.
There is also plastic deformation
of the rail.
And a loss of section due to corrosion.
There's a few examples of rail
we have here.
This sample here shows a fatigue crack
which is initiated
from the surface of the rail.
It's caused by the
repeated passage of wheels
over the surface
which will initiate small cracks.
And then, through fatigue,
this will grow progressively
over a long period of time.
The discolouration and classic markings
you can see here are a result of
the surface becoming oxidised
and corroded where it becomes exposed
to the elements.
Surface damage and
rolling contact fatigue
is our biggest cause of problems.
It accounts for something like
50%-60% of all defects
we remove from track each year.
Other forms of fatigue that we see...
Here we have a large star crack
which is originated from the bolt-hole
at a rail end.
Equally these are defects
we need to manage.
If they are allowed to go to failure
it can result in
a piece of the rail head
becoming detached.
Plastic deformation is another thing
we see where the rails degrade.
This is where the rails
are physically deformed.
They are spread;
the rail steel itself
is distorted and deformed
under traffic.
You can see the start of a small split
within the middle of the web.
These will propagate under traffic
if not managed.
They'll grow to a larger size,
the split will open up
and in extreme cases can result in
a piece of the rail becoming detached.
Most of our defects of this type
occur in older rails where there are
either inclusions or impurities
within the rail steel
which form a point of weakness
which, under repeated loading,
will cause the rail to fail.
Another type of degradation
is corrosion.
Here we have an example of a rail
removed from an aggressive environment,
where the foot of the rail
has corroded away, a large amount
of material has been lost.
This will result in rail failure
if the rail is not removed
in good time.
Aggressive areas are where
we would have exposure to water,
or perhaps the sea or salt water.
Level crossings are particularly bad
where we have a lot
of water from the road
and also during winter
salt is applied to the road
which causes a significant increase
in the rate of corrosion
in those locations.
And finally we have to deal with wear.
This can be either vertical wear
on the top of the rail
or side wear you can see here
on the side of the rail where the wheel
wears the rail away.
(Narrator) One of the most important ways
we manage rail is through inspection.
At Network Rail we use
a fleet of monitoring trains
to check on the condition of our track.
Monitoring vehicles allow us to cover
large quantities of rail miles
in regular cycles.
But in complex
switch and crossing layouts
we still need to inspect on foot
using portable kit.
(Brian) This piece of equipment here is a
Sperry Roller Search Unit
also known as "a Walking Stick".
This is used by our ultrasonic operators
who carry out a large amount of
pedestrian testing in areas where
we can't use vehicles to test
or in areas in lower category routes
where we don't programme the vehicles.
The ultrasonic equipment here
contains the Sperry Roller Search Unit
this contains 9 probes which are used
to scan the head and web of the rail,
the floor detector
which provides the signal and response
and is used to detect any defects
internally in the rail.
This is contained in a walking stick
to make it easy to push along the rail
to ensure the stick stays
aligned with the rail to carry out
the necessary inspections.
The inspection processes
that we use today, the frequencies and
the techniques and technologies
that we use have been developed
to minimise the risk of a rail breaking
to find defects in sufficient time
that we can plan their re-mediation.
If this isn't carried out
at the right frequencies
then we can end up, potentially,
with a catastrophic accident
similar to what happened in 2000
where the train derailed
because of a defective rail
at Hatfield.
(Narrator) Following inspection,
the next most important part
of rail management
is preventative maintenance
and the principal means
of preventative maintenance
are grinding and lubrication.
Grinding is carried out on our
main lines on a regular cyclic basis.
It maintains
the correct shape of the rail,
removes small surface imperfections,
and reduces the stresses
that lead to fatigue damage
in the surface of the rail.
We use lubrication
to minimise rail wear.
Track based lubrication equipment
deposits a small bead of grease
onto the wheel which is then
carried around the outside bend
of a curve.
Lubrication is used
on most tight curves on the network
to reduce rail wear and
the premature replacement of the rail.
Eventually, however,
it will be necessary
to replace the rail.
The primary reasons are the number
or severity of defects,
wear or corrosion.
Some rail can last up to 40 years
if on a straight piece of track.
But on the curves of a high speed line,
or where the rail is affected
by road salting
the lifespan can be reduced
to less than a year.
Typically, if a relatively short
section of rail needs to be replaced
this will be done at night
to minimise the disruption to traffic.
In this instance,
a corroded level crossing rail
is being removed and replaced.
The defective rail is cut out
and then removed from the site
using a road-rail vehicle.
Once clear,
the replacement section which has been
cut to the required length
is brought in and lowered into place.
This will be attached
to the existing line using
an aluminothermic weld.
First the rail is clamped
and hauled into position
and a mould assembled
around the two rail ends to be joined.
The rail ends are heated before welding
to prevent the rail steel
becoming brittle if it is allowed to
cool too quickly.
A crucible is placed on the mould.
It contains iron oxide
with specific alloying elements
and volatile aluminium powder which
causes the chemical reaction that
reduces the iron oxide into steel.
The chemical reaction
generates a huge amount of heat
that melts the constituents
to form liquid steel
which pours into the mould
fusing the rails together.
The mould and excess weld metal
is removed while it is still hot.
The stripped weld is then profiled
to exactly match the rail profile
and produce a smooth finish.
Following inspection,
the new level crossing rail
is ready to be used
as part of the network.
[TRAIN PASSES]
(Brian) The rail management engineer
continues to face
a significant challenge.
Modern expectations for 24-7 operation,
and modern vehicles,
whilst safer and more comfortable,
are often heavier.
These all result
in great amounts of damage.
One of the ways we can help combat
rail damage and deterioration
is the development of new materials.
A number of processes have been
employed to produce, traditionally,
harder and harder rail steels
to reduce wear.
Recently we've worked with Tata
to engineer a new steel which provides
not only a wear resistance but also
a resistance to fatigue damage.
This material, HP, we've just
started installation in track
and utilises some clever metallurgical
and chemical alloying additions
to produce a strong, premium grade
rail steel without the need
for expensive heat treatment.
This provides us with a
cheaper premium rail steel
with a similar performance
to some of the more expensive
heat treated steels
currently available.
(Narrator) Careful management of materials,
their specification, production,
maintenance and replacement
is a crucial part of rail engineering.
It allows us to maintain progress.
To keep trains running
safely and efficiently.
No matter what the demands of traffic,
line speed or location.