Two 15 m long stainless steel AISI 304 rods of diameter 864

Two 1.5 m long stainless steel (AISI 304) rods of diameter 864 mm are welded together end to end. For a post weld heat treatment purpose in order to strengthen the welded joint, the joint is to be maintained at 780°C for 2 hours. The rods are in air at 30°C with convection coefficient of 25 W/m2·K. What is the minimum power input needed to be applied at the joint for maintaining the required temperature?

Solution

POWER INPUT REQUIRED TO MAINTAIN THE TEMPERATURE,P = h*A*(T1-T2)*TIME

T1= TEMPERATURE OF JOINT = 780 DEGREE CELSIUS

T2 = TEMPERATURE OF SURROUNDING = 30 DEGREE CELSIUS

TIME = 2 HOUR

AREA,A =2(pi)RL*2

P,POWER = 25*2*3.14*(.864/2)*1.5*2*(780-30)*2*60*60 = 1098.7 MW