Pipes are generally cylindrical in structure of amount of heat loss through pipe is given by the formula

Q= 2 pi k L (T1-T2)/ln (r2/r1)

Where

k=conductivity of material of which pipe is made

T1= temperature of inside layer pipe

T2=temperature outside layer of pipe

L= length of pipe

r1= inner radius

r2=outer radius

ln=natural logarithm

pi=22/7

The above condition applies for steady state flow, single layer over cylinder and neglecting conductivity

To take conductivity into account term Q* must be added

Q*=2 pi L {r1 hi (Ti-T1) +r2 ho (T2-To)}

hi=convective coefficient for inside layer

ho=convective coefficient for outside layer

Ti= temperature of inside space of pipe

To=temperature of outside space of pipe