Formula for Heat loss in a pipe?

pips 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 logrithem pi=22/7 the above condition applies for steady state flow,single layer over cylinder and neglecting conductivity convection to take conductivity convection 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 for unsteady condition there is another formulaa