This week will introduce to you the whole system of maintenance and monitoring, and how smart usage can lead to reductions in maintenance costs!

On the next page, we will start by examining the Hatfield disaster, which indicates that for a railway system to operate safely, it is essential to have a proper maintenance plan. But one direct consequence of Hatfield: putting in speed restrictions for many sections of tracks, shows that maintenance can only be done when enough information is known about the quality of the track. So monitoring is essential as well, in order to be able to perform good maintenance. We’ll be covering these this week.

Maintenance is a very important aspect in all systems, even so for rail and train systems. Especially with public transport, where a lot of people use it and rely on the safety of this system.

A good example of why maintenance is so important is the ‘Hatfield Train Crash’. This is a train accident which occurred near London in England. On the 17th of October in 2000 a (GNER) Intercity from London bound for Leeds was travelling at 115 miles/hour (185 Km/h) when it derailed just south of Hatfield train station. The train then travelled for a further 1000 yards (900m) before coming to a complete stop. By then, the train had separated in three sections. The locomotive and first two coaches remained on the rails, but the sections behind it all derailed. The eighth car, which was the restaurant coach, overturned on its side. This coach was then severely damaged when it hit an overhead line gantry. The rest of the coaches derailed, but remained upright.

This all happened in less than 20 seconds. Sadly, 4 lives were lost and another 70 injured of which 3 seriously. The four people who died were all in the restaurant coach which overturned.

What is Maintenance?

Even under the most ideal circumstances, no building, structure or anything else human-made will last forever without human interference. Due to wear, but also natural processes, the quality will degrade over time. Maintenance is used to either repair or replace the degraded parts of the structure, in order to bring the quality back up to desired level. In some cases, maintenance might not be possible and a complete replacement of the whole structure is necessary. We can see maintenance in many aspects of our lives, for example, bringing your car to the garage or repainting your house.

For railways, maintenance takes place in many aspects of both the structure and the vehicles. The frequency of which this maintenance takes place will vary depending on the parts’ subjectivity to wear, as well as on the priorities set by the transporter and regulations set by governments.

Reactive maintenance is a common form of maintenance seen in many different fields. In reactive maintenance, one simply waits for a part to break before repairing it. This is often the ideal solution for small parts, which do not form an integrated part of a high-demand structure. This is, for example, how most people use their electronics: once it breaks, they either repair it or buy a new one.

In some cases, this strategy is also used on railways. In railways, the advantage of this system is the relatively low frequency of maintenance. You only send a team in when it is really necessary. However, once a part breaks, depending on the intensity of traffic on the track, the secondary costs can be very high. If a part of track is unavailable for a long period of time, there are severe economic costs related to this unavailability. Using reactive maintenance also brings certain risks with it. Some failures can lead to derailments of trains, resulting in severe damage or even fatalities. This makes reactive maintenance only suitable for parts of the tracks in which a single failure has no direct safety consequences or is automatically detected, resulting in an immediate stop of traffic.

In preventive maintenance, contrary to what is done in reactive maintenance, the goal is to prevent a structure or object from breaking by maintaining it in time. This is especially important if there are high costs concerned with the failure of the structure, or there is a risk of loss of life. Preventive maintenance is really common in, for example, the airline industry, but can also be seen in many other fields. Consider the maintenance of your car, which is often advised to be done after a certain distance has been driven.

In railways, preventive maintenance can have big advantages over reactive maintenance, mainly in financial aspects. Often maintaining a structure before it is broken is much cheaper than repairing it once it breaks, due to the difference in the techniques that can be used. Aside from that, in many countries the unavailability of railway tracks can have severe economic costs, which can be averted by using preventive maintenance.

Preventive maintenance does, however, bring some challenges though. It can be really hard to determine when to perform the preventive maintenance. There are two strategies that can be used for deciding this. These are known as fixed interval maintenance and condition based maintenance, they will be explained in the next unit.

Fixed interval

With fixed interval maintenance, the maintenance frequency is decided based on either a fixed time or a certain usage. For trains, this usage is usually defined as a certain number of kilometers driven. For railway tracks, maintenance can be done, for example, based on a number of axle passages or a certain summed total axle load. Determining which variable to use and setting the value for the interval can be a real challenge. In principle, the more frequent preventive maintenance is done, the less sudden failures will occur. However, high frequency maintenance will also mean higher costs. In order to be able to determine the optimal frequency for the maintenance, one would need to know the statistics of failure of all important components of a system. Often different components can have very different life-spans, thus making the optimum maintenance interval even harder to find.

Condition based

In condition based maintenance, the maintenance interval is not based on the average life expectancy of the object, but on the actual condition it is in at any given time. In order to determine when the maintenance is needed, sufficient data of the condition of the object is needed, combined with accurate models predicting the speed in which degradation will take place in the future. Monitoring is therefore an essential part of condition based maintenance.