Fire-free replacement tool for field oil transportation special-shaped pipe section and off-site prefabrication method

The invention relates to a fire-free replacement tool for a field oil transportation special-shaped pipe section and an off-site prefabrication method. Two welding platforms comprise U-shaped bottom plates, supporting legs are arranged at the bottoms of the U-shaped bottom plates, fixed vertical rods and adjustable vertical rods which are erected upwards and parallel to each other are connected to the U-shaped bottom plates, three-dimensional locking chucks are installed on the two vertical rods respectively, transverse supporting rods are clamped on the three-dimensional locking chucks, universal connectors capable of being locked are fixed to free ends of the transverse supporting rods respectively, and flange clamps and end pipeline clamps are fixed to the two universal connectors respectively; and openings of the two U-shaped bottom plates are opposite to each other and are connected with each other through platform connecting rods. After the two U-shaped bottom plates are fixedly connected, the fixed ver