Driving high performance track

Over many centuries, rail materials have changed to give improved performance in terms of rail life and load carrying ability.

From humble beginnings of wooden rails eventually strapped with iron to improve their life, the materials used have developed from wood, to cast iron, to wrought iron and eventually steel rails which form the basis of our railway networks today.

Steel rails themselves have developed over many decades and continue to do so in the quest for better performance. This article hopefully describes some of my experiences taking an idea from a coffee machine conversation to a product supporting a 125mph buffet car.

The need for better steel

Historically, the management of rolling contact fatigue (RCF), or head checks for European readers, has presented a challenge for many rail networks across the world. The use of longer-lasting, more wear-resistant rails increased the relevance of this degradation mechanism and its importance was crystallised by the incident at Hatfield in October 2000.

Managing RCF is both costly and time consuming in an industry that has a drive towards lower maintenance costs, shorter maintenance windows and greater track availability.

In response to the industry needs of doing more with less, Tata Steel set out to design a new rail steel that delivered improved rail life whilst also minimising maintenance requirements. This rail steel should be both resistant to wear and also resistant to RCF as a large proportion of track maintenance budget is focused around rail remediation and replacement due to these issues. The rail steel developed to address this need is called HP335, a High Performance rail steel with a minimum Brinell hardness of 335HB, (cf. standard R260 grade with a minimum hardness of 260HB).

Introducing a new and fundamentally critical product to the rail industry, which is traditionally rather risk averse, is always going to be a challenge. However, working in close partnership with Network Rail and other customers, Tata Steel has brought HP335 into use to demonstrate that large cost savings can be made by using the right rail in the right place.

Within two years of track testing, HP335 has achieved full product approval. In less than five years, it has commenced incorporation into both Network Rail and European rail standards and, most importantly, around 600km of it is now in use, delivering large life cycle cost savings. These equate to a seven-figure cost saving per year, delivered through reduced inspection and maintenance requirements and, of course, increased rail life. Key to achieving this product acceptance has been rigorous and transparent evaluation of material performance throughout the development process. It is one thing a company selling a product telling you a product is great; it is quite another when you see the benefits with your own eyes.

Three-stage process

Essentially the development was broken down into three main stages:

1. Proof of concept – laboratory testing;
2. Proving real life benefits – trial sites on
real networks;
3. Facilitating widespread adoption – standardisation.

The first stage of proving the concept ranged from laboratory tests, carried out on small scale samples of around 50kg of steel, through to producing a pilot-scale seven tonne cast of material from which to make full rails, and then trialling these in our own internal rail network where they are subject to 46 tonne axle loads (sometimes owning the biggest private rail network in the UK has its benefits in rail product development). This stage proved that potential benefits were there to be had and that there were no unmanageable risks moving to the next stage of testing – introducing rail into the public network.

The second stage required significant commitment from both Tata Steel and Network Rail to select suitable live trial sites for performance data gathering. These sites were to be monitored intensively for long periods of time (up to five years) to evaluate the real life performance of this new product.

Initially, just two trial sites were identified. However the significant performance benefits achieved, combined with the confidence built in the product in use, precipitated an expansion in the number of sites to be monitored on Network Rail infrastructure to a total of seven. There is also one monitored site on the Sheffield Supertram light rail network which actually took the honour of being the first customer installation of HP335.

Major performance improvements

Whilst it is vital to understand the performance of the new rail steel at a location, it is also equally important to understand how the rails previously installed there performed. After all, if there is no information on what went before, how do you know what better performance looks like?

The trial sites were monitored both before and after the new rail installation, and historic maintenance information for the sites was shared to get a good baseline of standard-grade rail performance. Regular site monitoring with teams from both Tata Steel and Network Rail, and the sharing of all the information gathered, ensured transparency of the material performance. Site monitoring was carried out in all weathers to ensure data was collected at appropriate intervals.

Agreed projections for life cycle costs on one site were made after one year of data had been collected and again revised after four years. The two results were found to be within 1% of each other, giving confidence in the projected cost savings that were achievable. Over a period of five years, and using four years of monitoring information, the rail management costs (rail purchase, installation, inspection and grinding) on one site were reduced by 52%. Rail life spans were commonly doubled from that of previous rails whilst reduction in grinding by a factor of three was observed on some sites.

From the vast quantities of site monitoring data, where HP335 rails had accumulated over 700 million tonnes of traffic, there were clear improvements in performance for every major rail degradation mechanism. Wear rates were greatly reduced, RCF was slowed, plastic flow reduced, spalling of low rails avoided and, last but not least, corrugation growth rates halved.

The confidence built from actual track testing under such close monitoring allowed full product approval to be granted in 2012, just two years after the first rail was installed for evaluation.

Snow monitoring.

So product approval had been obtained, but the process does not end there. Rail maintenance standards needed revision to provide guidance on when to use the product and, of course, the rail product standards themselves require revising to incorporate these new materials. Both the Network Rail and European rail standards are being revised to incorporate HP335 although, as is often the case, the standards tend to lag behind somewhat.

The message spreads

Whilst most of the site monitoring information was gathered on Network Rail infrastructure, other infrastructure owners and maintainers have been taking keen note. Customers are already adopting HP335 for their rail renewals in conventional, light and heavy haul rail applications to resolve different rail degradation issues that they face. In contrast to conventional rail, the key benefits for light rail usage are the improved corrugation and wear resistance, whilst in heavy haul applications it is the improved resistance to plastic flow with good wear resistance that delivers the needed performance improvements.

The first installations of HP335 outside of the UK are due shortly, with rails being installed in both Finland and France to address the issues of both RCF and wear, as audiences outside the UK begin to recognise the benefits it can offer over standard grade rails.

Of course, with every new product development, not everything goes smoothly all the time, but I am proud to be part of an extended team that has worked to provide solutions rather than barriers to exploiting the benefits on offer, as we all have a common aim – a sustainable and efficient rail industry. In the UK there is still a way to go to realise the full benefits of introducing this new rail steel. To date around 2% of the Network Rail infrastructure utilises HP335, whilst the European Innotrack project indicates that 30% of the UK network would benefit from using a premium rail (such as HP335). So it looks like we still have much work to do.

Written by Daniel Pyke, product marketing manager at Tata Steel Europe