A 150 mini steam pipe has inside diameter of 120 mm end pushed diameter of left nun. It is insulated at the outside with asbestos. The steam temperature is 150 °C and the air temperature is 20 °C, the heat transfer coefficient to wins inside is 100 W/m? °C and air outside is 30 W/m? °C respectively, and K for asbestos and steel is 0.8 W/m°C and 42 W/m°C respectivels. What thickness of asbestos is required limit the heat loss to 2.1 kW/m?