Niobium microalloying element

Obtained by producing killed steel, made to fine grain practice, and with microalloying elements such as niobium, vanadium titanium, and zirconium in the composition. 

The reformer tubes typically operate at maximum temperatures of 1,600°F to 1,700°F and are designed for a minimum stress-to-rupture life of 100,000 operating hours. A 35/25 Ni/Cr alloy is used that is modified with niobium and microalloyed with trace elements such as titanium and zirconium. Smaller tube diameters provide better heat transfer and cooler walls. This reduces tube and fuel costs and increases tube life. But more tubes increases the pressure drop. The optimum inside tube diameter is 4 to 5 in. The wall thickness may be as low as 0.25 inch with a length of 40 to 45 ft. The lane spacing between tube rows must be enough to avoid flame impingement from the burners. Typical spacing is 6 to 8 feet. 

Reformer tubes typically operate at maximum temperatures of 1600 to 1700°F and are designed for a minimum stress-to-rupture life of 100,000 operating hours. Today s preferred metallurgy is a 35/25 Ni/Cr alloy modified with niobium and microalloyed with trace elements including titanium and zirconium. 

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