Welding method for sealing girth of storage tank with diameter of 5M, weak rigidity and small-diameter manhole

The embodiment of the invention provides a welding method for a sealing girth of a storage tank with the diameter of 5M, weak rigidity and a small-diameter manhole. According to the welding method, high-efficiency sealing welding can be realized, and an inner supporting device for supporting a tank body is enabled to retract from a manhole flange. The welding method for the sealing girth of the storage tank with the diameter of 5M, the weak rigidity and the small-diameter manhole comprises the following steps: uniformly arranging a plurality of thrust angle plates in the circumferential direction of the inner surface, close to the sealing girth, of the front bottom, wherein each thrust angle plate comprises a circumferential thrust sheet (1) and a radial thrust sheet (2); conveying the inner supporting device of a detachable rod system in the front bottom through the manhole flange on the front bottom and assembling to form, wherein the inner supporting device of the detachable rod system comprises a plurality of inner supporting blocks; butting the front bottom with a cylinder section, and rounding the inner supporting device of the detachable rod system, wherein each inner supporting block is correspondingly attached to the circumferential thrust sheet (1) of one thrust angle plate; welding the sealing girth between the front bottom and the cylinder section.