INTRO: There is ample evidence to suggest that a preventive rail maintenance regime using a regular grinding programme can keep rail defects under control and lead to significant cost savings. Failure to maintain the rail leads to higher rail purchase costs and financial penalties
BYLINE: Dr Stuart L Grassie and Paul Baker*
IN EUROPE, winter is again in retreat. With it go some of the problems encountered by Britain’s railway operators and maintainers. But several of last year’s difficulties remain as challenges for the year ahead. Track engineers will have no difficulty in recalling the recent intense media interest in broken rails on the Railtrack network (RG 6.99 p346), and are well aware of the need to tackle the problem.
Clearly, there must be something amiss on a railway where the number of rail breaks increased from 656 in 1994-95 to 801 in 1997-98 and 937 in 1998-99 1. The obvious questions to ask are why has there been an increase, and what, if anything, can be done about it?
Experience elsewhere suggests that the answer to the second question is probably ’a great deal’. Not only can rail breaks be reduced, but so too can rail replacement and the overall cost of replacing and maintaining rail. This article outlines some of these costs and discusses lessons which may be learnt from the experience of others.
The cost of rail breaks
Fortunately, very few of these 900 or so rail breaks give rise to a derailment. At present, however, it is inevitable not only that some rails will break in service but also that others will be removed prematurely. These problems exist worldwide, not just in Britain. This article contends that routine rail maintenance helps to reduce both the premature failures and the premature renewals.
To a large extent, these problems arise because some of the rail breaks occur from surface-initiated cracks known as head checks or gauge corner cracking. Although these cracks exist on almost every railway, the instrumentation that is routinely used to measure and quantify the severity of surface-initiated cracks is inadequate. Consequently it is inevitable that there are inadequate procedures to help plan when to remove a rail to avoid a break while maximising useful service life.
If a rail does break in service, both direct and consequential costs are considerable. As it happens, the indirect costs are made more transparent than they might otherwise be thanks to the unique contractual regime in Britain.
A break is often detected by a signalling fault through the existence of track circuits; occasionally train crew report a suspected fault. An emergency gang is then sent out to check, and if necessary, replace the apparently defective section of rail. It is usual for about 4hours to elapse from the time that a possible break is detected until the track is restored to line speed.
During these 4 hours, it is typical for the accumulated train delay to amount to about 20h. In Britain, an organisation - usually the maintenance contractor - is held responsible for this delay and is liable to pay a penalty. This can be £100 or more per minute, or £6000 per hour, on a busy line in the rush hour. A more typical penalty for the 20hours of train delay is £40000, or £2000 an hour. Other costs are borne directly by the maintenance contractor for the emergency gang and their equipment, and indirectly by the passengers who are delayed.
Rail damage
The rail is a highly stressed component. Each wheel which passes induces localised contact stresses which would exceed the elastic limit of the rail steel if it were not for the protective residual stresses built up in the rail from initial cycles of loading. These residual stresses may also be close to the elastic limit. Typically, a rail experiences millions of loading cycles every year.
Engineering components which operate in such an environment usually receive some form of maintenance to minimise damage. For rails, damage generally takes the form of so-called rolling contact fatigue (RCF) or corrugation 2.
Both types of damage are particularly prevalent in curves, largely because of the high tractive loads which are generated to steer wheelsets through a curve. Leading wheelsets in a bogie tend to apply high lateral loads, which are believed to be primarily responsible for head checks. Trailing wheelsets generate high longitudinal forces, which are responsible for most types of corrugation that occur in curves 3.
One reason for the increasing severity of head checking throughout Europe may be that trains are running at higher speeds. The simplest way to improve high speed stability is to increase the in-plane primary suspension stiffness and damping. Higher tangential forces are required to steer the stiffer bogie through curves.
Experience elsewhere
The principal form of maintenance for a rail is grinding, which can remove both RCF cracking and corrugation from the rail surface. Railways worldwide are increasingly adopting grinding for their routine maintenance procedure for rails. Its adoption in Europe is, however, rather tentative at present as a result of characteristic conservatism and a great deal of apprehension. This is no less the case because the use of grinding as a routine maintenance procedure has overwhelmingly been developed in North America, and more specifically in Canada.
The point about use of grinding in this way is illustrated by reference to the relevant literature. The title of one paper stands out: Prolonging Rail Life through Rail Grinding. This reports on RCF damage that occurred rapidly on Canadian National soon after rails were put into service. Grinding trials were undertaken to reprofile the rail, with the result that ’spalling stopped’. This paper dates from 1986, and describes tests which started in 1984 4. Similar work was under way on CP Rail, and similar conclusions were being drawn 5. In the age of the Internet, some news takes a long time to travel!
These were early days on CN and CP, and they too were at that time somewhat apprehensive about their approach to RCF damage. However, they had seen that past practice had not worked, and they were willing to take a risk to prevent rails falling apart around them.
Relevance to Europe
A more recent paper from CP Rail shows how much the railway has benefited from taking a risk 6. The principal benefit has been in reduced rail replacements: from 435 track-km to 120 track-km between 1982 and 1995 (Fig 1). These figures represent about 2·4% and 0·75% of the 17000 track km network, and almost directly reflect Railtrack’s reduction in rail replacements over the same period 7. A figure of 2 to 3% is typical of main land Europe. CP Rail have benefited from a reduction in rail service defects over the same period (Fig 2). CP Rail and other railways with similar experience believe that these benefits have come mainly from an increase in grinding, particularly in curves, and a more appropriate application of grinding. On CP, the distance ground each year has increased from 17% to 88% of the total track length (Fig 3), compared with 10 to 20% in mainland Europe and less in Britain. Particular attention has been paid to lubrication, friction management and the wheel/rail interface in general.
The cost of grinding has also come down on CP, mainly by increasing the average speed at which rail is ground (Fig 4). Most track is now ground in a single pass, with large grinding trains, typically with 88 stones.
Some would argue that these results are not relevant to Europe because conditions are different. Indeed they are: lines in Canada typically carry traffic with 35 to 40 tonne axleloads compared with 22·5 tonnes in Europe; main lines handle upwards of 80 million gross tonnes per annum (three to four times that on Europe’s busiest main lines); loads are carried in wagons with three-piece bogies, whose primary suspension is primitive to the point of non-existence; and lines wind through mountain ranges and along sinuous rivers.
It would be a brave person who argued that European conditions for RCF are worse than these and that their solutions are accordingly of no relevance to Europe. The rails see loads from wheels; they don’t care whether the wheels carry wheat, iron ore, containers or people.
One European railway, Banverket, has begun to maintain some of its rails in this manner. After only three years of such routine maintenance on the Malmbanan iron-ore line in the north of Sweden, rail replacements have plunged to a small fraction of previous levels, and the rail surface quality has improved dramatically. Clearly this experience is still fairly limited, but the results to date are extremely encouraging.
Routine maintenance is good for your rails as well as for every other highly stressed, heavily working engineering component. It would probably be extremely attractive to most European railways if the life of their rails approached that which is now regarded as ’typical’ in North America: 330 MGT in 180m radius curves, 510 MGT in 450m radius curves and 1000 MGT in tangent 8. Routine grinding would also keep corrugation under control, thereby limiting wheel/rail noise and reducing track damage.
Savings
Some figures are presented in Table I to illustrate the savings which could in principle be achieved by implementing a policy of routine rail maintenance to move from a state in which 2 to 3% of rail is replaced every year, and relatively little is maintained routinely, to a state in which routine maintenance is the norm and there is much less rail replacement.
As the figures are so large and there are several unknowns, the table can be no more than illustrative, but the potential savings are nonetheless impressive.
TABLE: Table I. Illustrative costs of rail maintenance strategies
% of Cost Total
network euros cost 1
per km m euros
Current
Rail replacement 2·5 200000 100
Rail grinding 15 7000 2 21
Total 121
Alternative
Rail replacement 0·8 200000 32
Rail grinding 50 3 3500 4 35
Total 67
Overall saving 5 54
1. Assuming 20000 km of track2. Quoted in ref 9.3. At intervals of 15 to 25 MGT4. Assumption that cost of grinding per finished km could be reduced by approximately half if this were undertaken as part of a routine maintenance policy such as preventative grinding.5. Possible savings from reduction in rail breaks not included; however, an illustrative cost of 900 rail breaks in Britain at 65000 euros each = 59 million euros.
References
1. HSE Targets Broken Rails in Attack on Railtrack Record, Professional Engineering, December 8 1999, p4.
2. Grassie S L and Kalousek J, Rolling Contact Fatigue of Rails: Characteristics, Causes and Treatments, Proceedings of Sixth International Heavy Haul Railway Conference, Cape Town, 1997, pp381-404.
3. Grassie S L and Kalousek J, Rail Corrugation: Characteristics, Causes and Treatments, Journal of Rail & Rapid Transit, Proceedings of IMechE, 1993, 207F, pp57-68.
4. Worth A W, Hornaday J R and Richards P R, Prolonging Rail Life through Rail Grinding, Paper 1B-9, Third IHHA Conference, Vancouver, 1986.
5. Lamson S T and Roney M D, Development of Rail Profile Grinding on CP Rail, Paper 1B-8, Third IHHA Conference, Vancouver, 1986.
6. Young A, ARM Seminar, Chicago, May 1996.
7. Railway Finances, Fourth Report of the Transport Committee of the House of Commons, HMSO, London, 1995, Vol 1, Para. 98.
8. Mentioned by Roy Allen of the AAR in Specialist Technical Session on the Wheel/Rail Interface, IHHA, Moscow, June 1999.
9. Van Wijngaarden P, Environmental and Economic Aspects of Rail Grinding, Proceedings of Workshop on Rail Roughness Measurements, Utrecht, 1999
* Dr Stuart Grassie is a consultant working on problems of vehicle/track interaction and Paul Baker is Operations Manager (South), Balfour Beatty Rail Maintenance Ltd, York, Great Britain
CAPTION: Routine grinding can greatly extend the life of rail. This Loram grinder is shown working in Sweden
CAPTION: Left: Fig 1. Length of new rail, measured in track-km, laid on CP Rail, 1982-95
Right: Fig 2. Rail service defects on the CP Rail network in 1982-94
CAPTION: Two examples of spalling. Even rails which are as severely spalled as these can remain
in service if
they are ground appropriately
CAPTION: Left: Fine headchecks. Head checks are widespread on European railways, and appear to be on the rise. This may result in part from stiffer bogies being increasingly used to allow running at high speeds
CAPTION: Left: Fig 3. Length of rail treated with rail grinding on CP Rail in 1982-94
Right: Fig 4. Grinding productivity on CP Rail during 1982-94
Summary in French, German and Spanish:
Preventive grinding extends rail life and cuts maintenance.
Experience in North America and elsewhere suggests that a programme of preventive rail grinding has several significant benefits. Grinding reduces rail failures and extends the life of rail, leading to a fall in purchase costs. It also reduces the need for emergency maintenance and the ensuing costs arising from train delays with possible financial penalties. Further, it keeps noise levels relatively low by avoiding the growth of corrugations. In a controlled programme, the cost of grinding itself may also be lower.
Le meulage préventif allonge la durée de vie des rails et réduit les coûts de maintenance
L’expérience de l’Amérique du Nord et d’autres lieux fait apparaître qu’un programme de meulage préventif présente plusieurs avantages significatifs. Le meulage peut réduire les défauts des rails et allonger leur durée de vie, conduisant à une diminution des coûts d’acquisition. Il réduit également les besoins d’interventions d’urgence réduisant en même temps les coûts dus aux retards des trains, avec, à la clé, des possibles pénalités financières. De plus, le niveau de bruit est abaissé à un niveau relativement bas, le meulage évitant l’accroissement de l’usure ondulatoire. Inclus dans un programme planifié, le coût du meulage peut lui-même se révéler attractif
Präventives Schleifen verlängert Gleis-Lebensdauer und reduziert Wartungskosten
Erfahrungen in Nordamerika und anderswo weisen darauf hin, dass ein Programm für präventives Schleifen der Schienen wesentliche Vorteile bringt. Schleifen kann Ausfälle reduzieren und die Lebensdauer der Schienen verlängen, was zu verminderten Beschaffungskosten führt. Zudem werden Noteinsätze vermindert, welche wiederum die durch Zugsverspätungen und damit verbundenen Strafgebühren verursachten Kosten reduziert. Ausserdem hält das Schleifen den Geräuschpegel niedrig, da das Wachsen von Riffeln verhindert wird. Dank kontrollierter Planung k
