Nuclear power plant enterprises are generally equipped with a large number of steel containers. The container cylinder is equipped with signal holes at positions such as reinforcement rings, lifting lug connection plates, and support pads. After the container is in service, the signal hole exists only with the single function of monitoring whether the container leaks, and there has never been any professional in-service inspection for it. After a certain period of time, the corresponding part of the signal hole without inspection leaks, and the safe operation of the container is threatened. The plugging problem of signal holes in steel containers(any other metal containers are also applicable) were analysed and discussed. For the first time, a new type of plugging device was researched and developed, which could avoid crevice corrosion in the signal hole area. After practical application, the integrity and reliability of the container system of nuclear power plants were effectively improved, and the nuclear safety was effectively guaranteed. The plugging device is not limited to nuclear power plants and steel categories. It has reference significance for other industries and containers made of other materials.