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Stop the rot

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Britain’s steel industry has experienced a turbulent time of late. With weekly, and indeed even daily, media reports of doom and gloom in UK steel, it is easy to miss the good news stories that so often get buried by the bad. In the midst of all the turmoil and upheaval, and justifiable concern for the giant works at Port Talbot and its workers, the future of UK steel production is secure up at Scunthorpe.

That’s because 1 July saw the launch of a new (old) name in steel – British Steel. Formed from the sale of Tata Steel’s Long Products Europe business, British Steel rises Phoenix-like from the ashes of the UK steel industry sporting a completely new brand but building on its long heritage supplying rail, wire rod, special profiles and steel sections worldwide.

While British Steel will be a familiar name to many, the company has certainly changed since the last time rails bore the British Steel marque. Leaner, fitter and more agile, the core company values are ‘Pride, Passion and Performance’ – values the newly launched company intends to live by.

Dual defence

Whilst the company’s marketing department has been going into meltdown, launching and rebranding the new name in steel, its technical boffins have also been busy. Just one week after the launch of the new company identity, the rail team has officially unveiled its Zinoco® corrosion resistant rails to the world. Building on the performance of its previous protected products, Zinoco has already received product approval from Network Rail, London Underground and RATP with contracts secured across the UK, Ireland and France.

Zinoco is a premium coated rail that can withstand the harsh environments where corrosion determines rail life, in areas such as coastal routes, wet tunnels, level crossings, mineral lines and salt pans. Zinoco, which derives from the words ‘zinc for no corrosion’, offers superior corrosion protection compared to all current rail coating technologies. It offers a dual line of defence against corrosion employing both barrier and cathodic protection methods to enhance rail life. This dual defence means that it is suitable for use in areas subject to stray currents such as third and fourth-rail areas, amongst other problematic locations.

rail corrosion west barnes 6 months - uncoated
Corrosion ate away the foot of this unprotected rail in less than 6 months.

Extensive testing shows Zinoco will typically outlast traditional uncoated rail by around five times in a broad range of aggressive environments. It was developed in direct response to Network Rail’s request for more durable corrosion protection, calling for a coating that would withstand the rigours of real-life installation and use.

So the design brief was for an impact- resistant product that would withstand minor mechanical damage and Zinoco fulfils this, offering long-term durable protection. To produce it, a new Zinoco plant has been built at British Steel’s Scunthorpe plant with the automated facility coating rails more efficiently and consistently than previous products.

With the steel industry in such a state of flux, investing in building a new production plant underlines the confidence in the performance improvement Zinoco® offers.

Corrosive cocktail

One of the questions often asked is, does the industry really need rust-resistant rails? In the majority of cases, no, it doesn’t. If a rail’s life is determined by wear, then it doesn’t need extra corrosion protection.

rail corrosion dock hills 6 years - alphatek
This six-year old aluminium-coated rail is in a sorry state despite its original corrosion protection.

However, as rail networks improve the rails they use to extend their track life, rail corrosion and foot fatigue failure, often initiated by corrosion pits, make up an increasing proportion of rail replacements. There are specific locations which are prone to corrosion, and the rate of corrosion here can be far higher than many people might expect.

Common ‘rot spots’ are level crossings. Here the crossing panels trap moisture, road salt and other detritus making a potent, corrosive cocktail. In some locations, rail life is counted in months rather than decades, so in such locations the need for corrosion-protected rails is very clear.

The road/rail/pedestrian interface at crossings also makes rail inspection and replacement far trickier than plain-line environments. To inspect the rails, road, rail and pedestrian traffic must be stopped, and then the crossing panels removed to reveal the rails beneath – no small task. The busier the crossing is, the bigger the problem becomes.

Likewise, rail replacement at such locations is not popular with either crossing traffic or indeed people living close by. Imagine closing both the railway and major road every six months to replace rusty rail! Does that really make sense when it can be avoided? I’d even go so far as to ask, if rail crossings are installed without corrosion protected rails, have the designers considered the future maintenance requirements of the site at all?

Other areas prone to corrosion include coastal routes, where sea- spray soaks the tracks with salt laden water; wet tunnels where the constantly damp environment can reek havoc; mineral and ore routes where spillage and dust contamination can corrode rails; and, further afield, salt pans where salinity combined with moisture condensing on cold rails can accelerate corrosion to excessive levels. While the last example isn’t really a UK, or perhaps even an EU problem, we certainly have our fair share of the rest.

It has always seemed slightly odd to me as a materials engineer that we go to great lengths to provide corrosion protection for lineside structures such as signals, OLE and bridges, yet the rail itself remains naked in a sea of salt-soaked sludge.

The most troubling thing about rail corrosion is that it is often unseen. Disguised in dark damp tunnels, concealed by crossing panels, festering under the foot of the rail, corrosion eats away at our precious asset and can be invisible to standard inspection techniques.

In the picture right, all appears normal when inspected from above. The view from below is a different matter. Sadly, the bottom of a rail can’t effectively be seen when it is clipped in place.

Much focus is understandably given to maintaining the head of the rail in a good and safe condition through grinding and various inspection techniques, but the foundations of the rail, its foot, must not be neglected. This area provides much of the rail’s strength and stability and neglecting it is akin to building a house on poor foundations.

Fatigue in the foot

One of the increasing forms of rail failure seen in service is that of foot fatigue failure. As other forms of failure are being prevented, by improved maintenance and the use of better rail types, this failure mechanism is becoming increasingly important.

The rail foot is under great tensile stress in service and damage or, as in the case below, corrosion pits in the rail foot can initiate a fatigue crack. These grow with time and are virtually invisible to current NDT techniques, ultimately causing unpredicted failure.

Although the number of rail failures in the UK is commendably decreasing to its lowest level yet, 55% of current rail failures are attributed to this failure mechanism in the UK. Aside from wholesale rail replacement (which as a rail manufacturer I of course endorse wholeheartedly!), it is a challenge to control this somewhat unpredictable failure mode, and corrosion protection will have its place to tackle this tricky task.

foot corrosion failure2
The thumbnail-shaped fatigue crack propagated from a corrosion pit on the underside of the rail foot. When it reached its current size, the rail failed, cracking vertically upwards from the fatigue crack.

Someone recently tried to convince me that they could see such foot fatigue defects with ultrasonic inspection until I asked how they intended to spot them when the defect wasn’t located directly under the web of the rail? I’m not sure I ever got an answer to that question; indeed I’m not sure they’ve spoken to me since…

As we seek ever-increasing life out of our rail assets and ask them to cope with more and more traffic, factors other than wear and rolling contact fatigue become important determining the life of rail. Corrosion can be one of these life-determining factors. Zinoco provides a simple yet elegant solution to this that works in the real world, providing robust rust protection for rails.

Minor surface damage from installation, track maintenance, even flying ballast may halt the protection other coatings offer in their tracks, but thanks to the Zinoco dual line of protection, offering both barrier and cathodic protection to the rail, it continues to protect in real world railways.

Daniel Pyke is product marketing manager at British Steel which has a new website at www.britishsteel.co.uk


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