The heating furnace is composed of upper and lower furnace bodies, and the shell is welded by H-shaped steel and thick steel plate. A low-load, long-life flexible heating plate is arranged in the furnace. The heating plate and the shell are made of several layers of aluminum silicate needle-punched blankets, which are light in weight and have good thermal insulation performance. The upper and lower furnace bodies are provided with a tensioning device, which is convenient for quick connection and disassembly. The heating furnace is used for partial annealing after welding of spiral tube rows and related tubes and header assemblies (corner welds) in boiler manufacturing. Or suitable for the overall heating treatment of various non-standard workpieces, can also be designed and processed according to customer needs!