Issues regarding temperature and pressure values for pipeline grades
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When recently studying the classification tables for BASF projects, I noticed that for some pipe grades, the temperature and pressure values do not correspond to those of the flanges made from the same material. For example, for a Class 150 grade with low-pressure steam as the medium, and pipe material of A106b/API 5Lb, along with flanges made of A105, the pressure value at temperatures below 100°C is 17.8 bar; however, for the range from -38°C to 50°C, this value rises to 19.6 bar
The temperature and pressure values for pipeline grades are determined based on engineering design and the pressure-bearing capacity of the materials. Flanges of Class 150 have different allowable pressure values at various temperatures; this difference may be due to safety considerations and changes in the properties of the material. In practical applications, engineers need to select appropriate materials and grades based on specific operating conditions (such as the type of medium, temperature, pressure, etc.) to ensure the safe and reliable operation of the piping system. In the examples you mentioned, where the pressure is 17.8 bar below 100°C and 19.6 bar from -38°C to 50°C, this is likely due to the increased brittleness of materials at low temperatures; therefore, the design pressure is raised to ensure safety. .
First, one should look at the values specified in the steel pipe standards and codes on which the materials are based; however, when steel pipes are used in pipelines, it is necessary to follow the specifications applicable to those pipelines. Pipeline specifications take more factors into account. I work in pipeline design; feel free to contact me via WeChat: 924549064