TPT July 2007

3.1 Higher product quality

• Pipes with thinner wall thickness (higher diameter-to-wall thickness ratio) • Closer wall thickness tolerances • Better diameter tolerances • Higher pipe surface smoothness

3.2 Larger product range

• Steel grades – with critical hot workability – can be rolled • Increased flexibility

3.3 Lower Production cost

• Higher yield • Reduced tooling wearing • Lower tooling inventory cost • Higher efficiency in production and in automatic process control

To expand upon these advantages of FQM™, it is worth explaining the major process features influencing each improvement. Tubes with higher D/t (diameter to wall thickness) ratios can be rolled. The substantially higher uniform deformation, with lower average and peak pressures, allow the rolling of tubes with thinner wall thicknesses in relationship to the diameter. Wall thickness tolerances are also considerably improved. The process tolerances are improved because the 3-roll arrangement ensures a considerably more uniform deformation, due to the lower differences in peripheral roll velocity and the closer roll pass design that can be used. The 3-roll arrangement also provides better stability and centring of the mandrel in the pass. The 3-roll pass also possesses a more favourable geometry. This leads to a substantial reduction of wall deviations that result from the operation of closing and opening the roll pass on the same mandrel to produce several wall thicknesses. Tube end wall thickness can also be notably reduced by AGC in order to compensate for the end thickening, which takes place when stretch is applied in the subsequent stretch-reducing mill.

From the point of view of the material deformation, the differences between the 2-roll RMM and the 3-roll FQM™ are significant. The smaller difference of the peripheral speeds between the groove bottom and the flange of the rolls leads to a more uniform deformation in the pass of an FQM. It is more uniform both in the steady phase and in the transient phases (biting and release). › Figure 3 : The 3-roll FQM mill (above) provides a more uniform deformation in the pass than was previously experienced with the 2-roll RMM process • Less redundant transversal material flow • Lower specific average and, particularly, peak pressures on the mandrel and on the rolls • Higher degree of stability of the mandrel in the pass The effect of this technological improvement results in a range of benefits. This benefit results in:

fi Figure 4 (below) : FQM – hot rolling is performed on a retained mandrel through a sequence on rolls driven stands Figure 5 (bottom) : The FQM is an adjustable 3-roll stand longitudinal rolling mill, which uses the retained mandrel technology typical of the 2-roll RMM, in combination with 3-roll pass design. The working cycle is similar to the RMM process cycle

The technology also achieves better OD accuracy of inline finished tube. Higher temperature uniformity across the section and along the mother tube permits closer tolerances on sizing of the tube outside diameter. Achieving a smoother tube surface is also possible, as the 3-roll pass rolling reduces slippage on the tube surface. This eliminates any trace of a mark on the outside surface. The inner surface quality, already excellent in the RMM process, is also improved. These benefits mean that more sophisticated steel grades can be successfully rolled. This advantage is possible because of the higher compressive circumferential stress conditions of the 3-roll pass. Process flexibility is increased, meaning that small lots of tubes can be processed in a wide range of

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J uly /A ugust 2007