Issues regarding the installation of safety valves in long-distance pipeline systems

The causes of overpressure in long-distance natural gas pipelines are mainly related to fires at the gas source (such as the compressor outlet) and within the station’s process areas. If there are reliable pressure relief measures at the gas source outlet, the long-distance pipeline itself will not experience overpressure; therefore, no safety pressure relief devices are necessary on the pipeline. However, during accidents or renovations, it is necessary to install vent pipes for the pipeline between the two line isolation valve chambers. The regulations only state that the pipeline venting time should be as quick as possible, but it is difficult to determine exactly when this should happen; therefore, it is hard to establish a basis for calculating the diameter. Station regulations require that a safety relief system be installed for entry and exit, so safety valves are generally installed at the entrance to the station. Its displacement is determined using the calculation methods specified in capacity regulations or chemical industry standards for the installation and selection of safety valves. The required discharge volume is the flow rate of the pipeline under the discharge pressure; another view holds that only the flow rate of the pressure-boosting section is necessary, but there is no clear regulatory basis for this. For systems equipped with pressure regulation devices and having inconsistent inlet and outlet pressures, a safety valve must be installed downstream. There are also two scenarios regarding the discharge volume of this safety valve. In the case of a monitored pressure regulation system equipped with a safety shut-off valve, the discharge rate is 1% of the flow rate; if it is not configured in this way, the discharge rate is then the flow rate at the discharge pressure.