Jacketed pipe for fuel gas pipeline and fuel gas system

The invention provides a jacketed pipe for a fuel gas pipeline and a fuel gas system, and relates to the technical field of fuel gas conveying pipeline equipment. The jacketed pipe is suitable for occasions where the fuel gas pipeline needs to be protected by a sleeve, is not limited by the length and pipe fittings, and is also extremely convenient to maintain. The jacketed pipe comprises a first straight pipe section, a second straight pipe section, an elbow section, a three-way section, a reducing section and a sealing detection device, wherein inner pipes of the first straight pipe section, the second straight pipe section, the elbow section, the three-way section and the reducing section are connected to form an inner pipe of the jacketed pipe; casing pipes of the first straight pipe section, the second straight pipe section, the elbow section, the three-way section and the reducing section are wrapped and sealed to form an outer pipe of the jacketed pipe; an interlayer cavity used for being filled with s