Discussion on the impact of pipeline pressure ratings on the selection of pipe fittings.
Thread Content
For a existing steam pipeline with a maximum operating pressure of 1.3 MPaG, a design temperature of 250°C, material grade 20, and pressure class PN16, according to the flange specifications in standard 20592, the maximum allowable pressure at a working temperature of 250°C is 1.2 MPaG. Therefore, under normal circumstances, PN25 should be used. But here’s the question: this applies only to flanges; what if there are no flanges? Is it sufficient to use welded connections for the valves? Or use PN25 for the flanges, while keeping the valves at PN16 and attempting to connect them forcefully~ (This probably won’t work.) If it’s a new installation, using PN25 will suffice; but what to do since the existing system uses PN16?
For this existing steam pipeline, with a maximum operating pressure of 1.3 MPaG, a design temperature of 250°C, material grade 20, and a pressure class of PN16, the following options are considered: 1. If there are no flanges and the valves are connected by welding, it is necessary to ensure that the pressure class of the valves meets the pipeline’s maximum operating pressure of 1.3 MPaG, in order to prevent safety issues such as leaks. It is recommended to refer to relevant standards or consult professionals at this time to select the appropriate valve pressure rating. 2. If the flange is PN25 while the valve is still PN16, forcing a connection is not advisable. Due to the mismatch in pressure ratings between the pipes and valves, this type of connection is prone to leaks and safety issues. It is recommended to replace the valve with one of PN25 pressure rating that matches the flange. 3. If it is a new installation, it is recommended to use fittings and valves with a PN25 pressure rating in accordance with the design requirements. However, if the pipeline has already been built and its pressure rating cannot be changed, it is necessary to assess the safety and reliability of the pipeline. If the assessment shows that safety and reliability can be ensured, the existing PN16 fittings and valves can continue to be used. If the assessment results indicate that the pipes and valves are not safe or reliable, it is necessary to consider replacing them in order to improve the safety and reliability of the piping system. .
Welded valves also have pressure and temperature ratings; verify whether PN16 is sufficient.
Flanges are not considered when it comes to pound rating
It can be checked using non-standard flanges; if it meets the requirements, a calculation report will be provided. With valves, it’s difficult; they can’t be calculated for, so only welded valves with special pressure ratings can be selected.
According to Table 2-29A in GBT 12224-2015, with the valve body material being WCB, a nominal pressure of PN16, and a temperature of 250°C, the maximum operating pressure is 1.32 Mpa; therefore, welding valves would suffice for this application.