Mont Blanc Tunnel Reopens
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SAFETY IN THE MONT BLANC TUNNEL has been improved significantly through the use of heat- and corrosion-resistant S31603 stainless steel for several key design elements. |
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STAINLESS STEEL CLADDING (above)has been used to anchor fibre cement panels to the walls of the tunnel and rock bolts (below), made from round bars of S31603 stainless steel, anchor the stainless steel shapes to the tunnel walls. |
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Nickel stainless steels are used to clad the tunnel walls, and in a new fire
suppression system
Nickel magazine, Feb. 2003 -- The Mont Blanc tunnel, near the French ski resort of
Chamonix, is a major, 11.6-kilometre highway link between France and Italy. It was reopened to traffic in
2002 after three years of extensive work to repair damage caused by a fatal truck fire in March 1999.
To prevent a similar tragedy from occuring, safety standards have been upgraded significantly. One of the main objectives was to improve both the active and passive means of fighting vehicle fires within the confined space of the tunnel and, to that end, the Italian National Road Authority (ANAS), issued new directives for rehabilitation work. These included the specification that nickel stainless steels be used as the structural material in key safety improvements. Stainless steel was chosen because of its ability to resist both corrosion and heat.
Nickel stainless steels have been used to fabricate ventilation fans that operate even in the presence of smoke and high temperatures. They were also used in the lighting equipment and ceiling cladding, and in the piping and fittings of the fire-suppression systems.
Stainless steel cladding was used to anchor fibre cement panels to the walls of the tunnel over an area totaling 20,000 square metres. The cladding, which is corrugated and consists of 0.5-millimetre-thick S31603 stainless steel sheet, fulfils the functions of waterproofing, drainage and fire resistance. Another important consideration was ease of fabrication in terms of simple rolling, forming and welding, and the material's resistance to corrosion means little maintenance will be required.
The walls along the full length of the Mont Blanc tunnel are clad with panels of fibre cement, and their finish and colour meet ANAS specifications. The clad plates are fastened to the tunnel wall with the aid of curved stainless steel strip and stainless steel anchor bolts.
The anchor bolts (see photo at left) are fabricated from round bars, also of S31603. They were tested at
high temperatures in accordance with ISO 834 specifications. The results proved that the anchoring system
resists deformation for at least two hours at temperatures up to 1,000°C. At higher temperatures failure
results from the thermal deterioration of the rock, rather than from a failure of the anchors. The
corrosion resistance of stainless steel is also important for another reason: since the formation of iron
oxides is eliminated, there is no increase in volume and therefore no loss in anchoring efficiency.
The tunnel's new fire supression system has been designed to guarantee safety, reliability and
efficiency. During the winter months, large volumes of ground water result in high hydraulic pressures
in the pipes that carry the water. S31603 stainless steel is sufficiently strong to withstand these
pressures. Three different diameters of pipes are used: 219.1, 168.3 and 114.3 millimetres. They are joined
by GTAW (TIG) or laser welding and assembled with the use of slip-on flanges.
Adapted, with permission, from the June 2002, No. 148 edition of "Inossidabile" published by Centro
Inox, the Italian Stainless Steel Development Association.
Photos: CENTRO INOX
 Centro Inox |
