Critical Thickness of Insulation - GATE ME '11

A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surrounding is 5 W/m^2K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/m.K. Which one of the following statements is TRUE? A. The outer radius of the pipe is equal to the critical radius. B. The outer radius of the pipe is less than the critical radius. C. Adding the insulation will reduce the heat loss. D. Adding the insulation will increase the heat loss.