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1. Pipeline pressure system: Domestic and international natural gas transmission and distribution systems all adopt high-pressure gas transmission along with single-medium-pressure pipeline distribution; the economic benefits and advantages in terms of operation and management that this approach offers are unmatched by traditional multi-stage pipeline systems. Therefore, this distribution method should be retained during renovation and expansion. The pressure grading system for natural gas transmission and distribution is primarily used to determine the pressures for high-pressure gas transmission and medium-pressure distribution. An appropriate pressure grading system not only ensures the needs of urban gas supply but also reduces investment in pipeline networks and gas storage facilities. Taking the natural gas renovation and expansion project in the main urban area of Chongqing as an example, the designed working pressure for the new ring-shaped gas pipeline was 1.6 MPa, while the working pressure for the new medium-pressure pipeline network was 0.4 MPa. The ring-shaped gas pipeline serves both the purpose of transporting gas and storing it. However, in practice it is difficult to ensure sufficient safety distances for gas pipelines, which is unacceptable to the planning and fire departments; as a result, the operating pressure of the gas pipelines was reduced to 0.8 MPa. Although the gas transmission capacity of the circumferential pipeline can meet the demand, its gas storage capacity has significantly decreased; as a result, the task of handling peak loads will mainly fall on the storage and distribution stations, which increases investment in gas storage facilities. In the renovation and expansion project, new high-pressure gas pipelines should, based on actual conditions, make use of the high pressure from the main long-distance pipelines as much as possible to increase the pressure of the gas pipelines, thereby reducing the costs associated with the pipeline network and gas storage facilities. Currently, beyond meeting the gas needs of residential users, natural gas is being utilized in various types of public buildings. Large-scale gas-consuming facilities such as direct-fired gas engines and gas stoves, which require large amounts of gas (several hundred to several thousand cubic meters per hour) and operate at high pressure levels (0.01 MPa–0.2 MPa), have become increasingly common, placing high demands on natural gas distribution networks. ·To meet the gas supply requirements as much as possible, the operating pressure of the medium-pressure distribution network should be set at the upper limit of Medium Pressure A, namely 0.4 MPa, to ensure the highest level of supply reliability. During renovation and expansion, the newly constructed medium-pressure pipeline network should be designed and constructed at 0.4 MPa, with its operating pressure determined based on actual conditions. The operating pressure of the new medium-pressure pipeline network, which must be connected to the existing pipeline network for operation, should be the same as that of the existing network; only after the existing network has been modified to meet the required standards can it operate at an operating pressure of 0.4 MPa. An independent newly built medium-pressure pipeline network should operate at a working pressure of 0.4 MPa. 2. Pressure regulation equipment: The medium-pressure single-stage pipeline distribution system for natural gas requires that all burners use pressure regulation equipment in order to be connected to the pipeline network. Residential and general public building users can still use building pressure regulators for gas supply; this is also a method that was widely used before the civil war and is permitted by regulations. —Special attention must be paid to the gas supply for medium-pressure burners such as gas direct-fired engines and gas boilers. From the perspective of gas supply safety, users with high gas supply pressure and large flow rates should implement necessary safety measures as well as more reliable pressure regulation equipment. The commonly used voltage regulation equipment (sometimes including metering) is cabinet-type voltage regulation equipment or underground voltage regulation equipment. Such pressure regulation equipment includes regulators with high capacity and precision, filters, control valves, safety shut-off valves, telemetry and remote control devices, as well as metering instruments. It can be configured in various ways such as 2+1 (two pressure regulation circuits plus one bypass circuit), 1+1 (one pressure regulation circuit plus one bypass circuit), or 2×0 (two pressure regulation circuits). Its reliability in supplying gas is much higher than that of building-level regulators, making it the ideal choice for supplying gas to appliances such as gas-fired engines and gas boilers. However, the current \"Code for Design of Urban Gas Systems\" does not mention such equipment; manufacturers refer to them as \"box-type pressure regulation stations\" or \"underground pressure regulation stations.\" As a result, fire departments determine their location based on the safety distances specified in fire and gas regulations for ordinary pressure regulation stations. Since public buildings that use combustion appliances such as gas direct-fired engines and gas boilers are usually large-scale facilities, fire departments generally specify a distance of 25 meters between cabinet-type pressure regulation equipment; the installation of underground pressure regulation equipment is not permitted. This largely limits the use of cabinet-type pressure regulation equipment or underground pressure regulation equipment, thereby restricting the development of high-flow combustion appliances such as gas direct-fired engines and gas boilers, and hindering the expansion of gas supply capacity. Therefore, in renovation and expansion projects, it is necessary to reach a consensus with the fire department regarding the installation and planning of various pressure regulation facilities, and establish fixed guidelines, in order to ensure the smooth progress of such projects. At the same time, it is recommended that the revision of the \"Code for Design of Urban Gas\" also take into account actual conditions by promptly including new equipment, new processes, new technologies, and new materials, so as to facilitate their adoption and the development of the gas industry. 3. Pipe materials: In the past, steel pipes were used for natural gas pipelines. However, with the gradual adoption of PE pipes, their advantages such as lower cost, longer service life, and easier installation have led to an increasing use of PE pipes in medium-pressure pipeline systems over the years. In renovation and expansion projects, PE pipes should be used for the new medium-pressure pipeline network. This will result in a situation where PE pipes and steel pipes are used together, causing significant difficulties in the maintenance and emergency repair of pipelines. Emergency repair teams must be equipped with repair tools for both steel pipes and PE pipes in order to ensure proper maintenance and repair operations. Therefore, in the renovation and expansion project, the use of four-pipe systems should be concentrated as much as possible within a specific area, while for the newly installed medium-pressure pipes in the areas where steel pipes were originally used, steel pipes remain the preferred choice. Indoor pipes are generally made of galvanized steel pipes or seamless steel pipes. Recently, aluminum-plastic composite pipes have been promoted for use; the gas industry should also keep up with the trends of the times. However, to date, there are no relevant technical specifications or standards in this area, which makes large-scale adoption difficult. This is one of the issues that need to be addressed urgently in renovation and expansion projects. 4. Metering: Metering includes the measurement of gas supply by the gas transmission department to gas companies, as well as the measurement of gas supply by gas companies to various users. The gas transmission department typically measures gas at the city gate stations; after modifications or expansions to the gas transmission system, it is important to ensure that the range of the measuring instruments changes accordingly. Gas companies should take into account pressure adjustments for various types of users when measuring consumption, otherwise the readings shown on the meters will be too low. For residential customers, the current problems include the inability to access homes for meter reading and difficulties in collecting gas fees; therefore, improvement measures should be taken as much as possible during renovation and expansion projects, such as installing outdoor meters, providing centralized display of meter readings, and using remote meter reading methods. 5. Gas supply under special circumstances: For the use of gas in high-rise buildings, basements, interior kitchens, and other such special situations, although the \"Code for Design of Urban Gas Systems\" provides relevant regulations, these are rather general. There are still many details that need to be addressed regarding the actual gas consumption of each building. Issues such as reserving spaces for gas pipelines during building design, installing exhaust systems in high-rise buildings, setting up gas leak detection and shutdown systems, and determining whether pressure relief valves are necessary in basements all require appropriate solutions to be developed as part of renovation and expansion projects. It is also necessary to reach an agreement with the planning and design authorities as well as the fire department; otherwise, some buildings will not be able to use natural gas, which can affect the outcome of the renovation and expansion work.