Large diameter welded pipe black annealing machine is a special machine for heating the steel pipe to solution temperature and then cool it to room temperature. this machine adopts the advanced induction heating power supply, the new typeDSP+IGBT power supply. It uses IGBT inverter, DSP precision control, air-cooling structure( water cooling for induction coil), reduce the loss of system. It has perfect self-protection and self diagnostic function,Saves 15% energyComparing with the similar product. It is the first machine that could annealing such large stainless steel welding pipes.