It is reported that the world's largest stainless steel roof is being built at the New Doha International Airport in Qatar. Shaped in a billowing, it symbolizes the Gulf emirate's aspiration to be a gateway to the world and sets new standards of elegance, comfort and convenience in air travel. The roof of the passenger terminal is made of a Moly grade lean duplex stainless steel.

New Doha International Airport promises to be an international gateway to the region that will showcase the cultural, technical and environmental achievements of this small but wealthy Gulf state. NDIA will comprise a new passenger terminal, an Emiri terminal complex, Qatar Airways' new headquarters, a public mosque, an 85 meter high control tower, cargo terminal buildings, hangars and other buildings. With two of the longest commercial runways in the world, the new airport will be among the first to accommodate the Airbus A380 double decker super jumbo.

When finished, NDIA will be about two thirds the size of Doha and 12 times larger than the current Doha international airport. It is expected that the new airport will generate additional commercial activity. For this reason a huge complex will be built alongside the airport, an area of over 100 hectares have been reserved for a hotel, an office and business park and a retail mall.

NDIA passenger terminal root: Facts and figures

But the terminal's most striking feature is its undulating roof, said to be the largest stainless steel roof in the world. Several factors had to be taken into account when selecting the stainless steel grade. The most important of these was the airport's close¬ness to the sea. The roof had to resist not only the heat and humidity found everywhere in the Middle East, but it also had to withstand salt corrosion on top of these other problems. Other factors included cost and a favorable strength to weight ratio.

Another important consideration was that the roof should not reflect too much sunlight, which would not only cause discomfort on the ground but also distract the pilots. Texture and appearance were therefore vital not only for aesthetic but also for practical reasons. To get these two factors right, Contrarian Metal Resources applied its proprietary InvariMatte® finish to the duplex stainless steel sheets. This non-directional, low-gloss, uniformly textured stainless steel finish is especially suited to surfaces where low reflectivity is required. The end result is extremely consistent, like paint, but, as there are no coatings to deteriorate, it can last much longer, without much maintenance.

Although this type of matte finish can be applied to stainless steel Types 304(L) and 316(L), it was a duplex stainless steel that was specified on this occasion. Contrarian Metal Resources turned to a local supplier of global renown, Pennsylvania-based ATI Allegheny Ludlum. The company's AL 2003™ lean duplex stainless steel (1.8% Mo, 21.5% Cr, 0.17% N, 3.7% Ni) turned out to have exactly the right properties for the task in hand. The manufac¬turers have stated that this grade has a substantial strength advantage over Type 316L, allowing thick¬ness reductions and therefore lighter weight; this translates into significant savings in raw material costs. Also, the corrosion resistance of this grade can be superior to 316L, even in as-welded condi¬tion. Especially where weight-to-strength ratio and chloride pitting resistance are important, certain grades of duplex stainless steel can be more suit¬able than 316L.AL 2003™ has in fact replaced 316L in some applications: for example, the pipes supporting the canopy for a Washington DC metro station, flexible flowlines for the Kikeh oil and gas project offshore Malaysia, and laser-welded tubes for a geothermal condenser.

AL 2003™ is the only lean duplex grade that contains moly in significant amounts. In this grade, moly is an indispensable ingredient in combating corrosion. This is vital in a region notorious for its hot, humid and saline atmosphere- especially as the airport site is virtually surrounded by sea.

(Sourced from Moly Review Jan’09 from International Molybdenum Association)