Principles for determining design pressure in pressure pipeline codes
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Pressure pipeline code GB/T20801.3-4.1.1.2 b) When the pipeline is directly connected to equipment to form a pressure system, the design pressure of the pipeline shall be no less than the design pressure of the equipment. According to this provision, the following question arises: When the operating pressure of the steam pipeline is 0.8 MPa, the set pressure of the safety valve installed on the pipeline is 0.9 MPa, and the design pressure of the pipeline can be taken as 1.0 MPa. But when the rated pressure of the boiler is 1.25 MPa, should the steam pipeline connected directly to the boiler use 1.25 MPa as the basis, with a design pressure greater than 1.25 MPa? Please advise~~
The rated pressure of the boiler is 1.25 MPa. Does this 1.25 MPa refer to the operating pressure or the design pressure of the boiler? If it’s a matter of design pressure, then it’s simple: the design pressure of the steam pipes connected directly to the equipment is increased to 1.25 MPa. If the set pressure of the safety valves on these pipes is also set at 1.25 MPa, then that’s sufficient
If the set pressure of the safety valve on the steam pipeline is 1.25 MPa for sections that are directly connected, it is 0.96 MPa, which corresponds to the design pressure of that section of the pipeline, for sections that are not directly connected; the operating pressure of the steam pipeline is 0.8 MPa.
As for whether the rated pressure of a boiler should be considered as the operating pressure or the design pressure of the pipes, I think the operating pressure is the more reliable figure, while the design pressure takes into account some margin for safety. So far, I haven’t seen any clear guidelines on this matter in China