Device and method for leak detection in narrow space of large pipeline seam

The invention belongs to the field of leakage point detection, particularly relates to a device and a method for leakage detection in a narrow space of a large pipeline seam, and aims to solve the problem that leakage point detection cannot be performed on a welding spot of a steel plate body and telescopic compensation equipment in a long trunk pipeline in the prior art. The method comprises the steps that a connecting mechanism is installed between adjacent steel plates, a narrow space is formed between the connecting mechanism and the steel plates, and a sealing device is installed in a gap between the adjacent steel plates and used for isolating the narrow space from the outside; an airflow channel is arranged in the sealing device and communicated with an air inlet and an air outlet, the air inlet and the air outlet are formed in the two sides of the sealing device respectively and extend into the narrow space, the air inlet is used for injecting helium, and the air outlet is used for discharging air in