A submerged arc-welding operation under automatic control is used to butt weld two round steel tubes with diameters = 2.0 m. The tubes are slowly rotated under a stationary welding head to complete the weld seam. Welding voltage = 25 volts, and current = X1 amps. The heat transfer factor for SAW = 0.95, and the melting factor = 0.8. Cross-sectional area of the weld bead = 50.0 mm2 . If the melting temperature of the steel = 1490°C, and its unit melting energy = 10.3 J/mm3, determine the (a) rotational speed of the tubes and (b) time required to weld the seam