Preheating before welding is done to

The cross section weld bead is shown in fig the profile of the bead and the fusion zone are taken circular for convenience. Bead width and radii of curvature of circular profiles are given in fig. The bead height and depth of penetration are

Tool life of a $$10$$ hours is obtained when cutting with a single point tool at $$63m/min.$$ If Taylor's constant $$C=257.35,$$ tool life on doubling the velocity will be