How to select the pressure rating of flanges and valves based on the design pressure of the pipeline

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I would like to ask the experts: how do pipeline design engineers determine the pressure rating of valves and the pressure rating of flanges based on the design pressure and temperature? Specifically as follows: First, based on what standards or theories are the valve pressure class and flange pressure class determined, using design pressure and temperature as references? For example, I have seen that the parameters provided on the valve data sheets supplied by pipeline design engineers or owners are as follows: First type: Medium – purified natural gas; maximum operating pressure of 10 MPa; valve pressure class – Class 600; medium temperature range – -20 to +70°C; pipe fittings made of 316 material; size specified as Dxxx*t; flange standard – ASME B16.5 RF; matching flanges are provided. Second type: Medium – purified natural gas; maximum operating pressure of 10 MPa; valve pressure class: Class 600; medium temperature range: -20 to +70°C; pipe fittings made of L245N with dimensions of Dxxx*t; flange standard: ASME B16.5 RF; matching flanges are provided. Is this specified pressure rating unreasonable (explained below)? II. Based on the data provided above, the valves and flanges do not meet the requirements of ASME B16.34 and B16.5 standards. The details are as follows: 1. On the data sheet, for purified natural gas, valve bodies made of A105 or WCB are typically used (with L245 fittings), while 316 valve bodies are used for fittings made of 316 material. Therefore, for B16.34, the rated pressure values of these two materials at 70°C are both below 10 MPa. Using interpolation, the rated operating pressure of WCB/A105 at 70°C is 9.74 MPa, while the rated operating pressure of 316 at 70°C is 9.15 MPa. Clearly, neither A105/WCB nor 316 can withstand the maximum operating pressure of the pipe; if a material that can handle such pressure is used, such as a nickel-based alloy, it would be more economical to raise the pressure class to Class 900 instead. 2. Matching flanges must be provided; obviously, depending on the material of the pipe fittings, A105 and 316 are suitable choices for such flanges. According to ASME B16.5, the rated working pressure of WCB/A105 at 70°C is 9.74 MPa, while that of 316 at 70°C is 9.15 MPa. It also means that the flange material cannot meet the maximum operating pressure requirements of the pipeline, and it is not possible to replace the flange with a material that can withstand such pressures, such as nickel-based alloys. III. Given the above situation, I am here to seek advice from the experts: 1. In this case, the pipeline design engineer has specified a maximum operating pressure of 10 MPa and set the pressure class at Class 600. Is this in compliance with relevant design codes or standards? Are there any such codes or standards? 2. In this case, if the data sheet provided by the design engineer shows a design pressure of 10 MPa (note: it is the design pressure), with a pressure class set at Class 600, does this comply with relevant design codes or standards? Are there any such codes or standards that establish a relationship between the design pressure and the operating pressure? 3. As a supplier, since the data sheet specifies the pressure rating, it is often not considered necessary to verify the relevant standards; therefore, the valves and matching flanges are supplied according to the pressure rating indicated on the data sheet. But this actually doesn’t meet the standards either; how can we avoid this situation? 4. Was it ultimately my inadequate understanding of the pressure ratings in the ASME B16.34 and B16.5 standards that led to the above misunderstanding? 5. If it does not meet the standards and is discovered by the supervision team afterwards, is it the supplier’s failure to bring this up, or is the pipeline design engineer also responsible? I thank all the experts for their thorough discussions. And it’s usually the case with such data sheets: either the design pressure is 10 MPa, or the maximum operating pressure is 10 MPa, or the maximum pressure difference is 10 MPa; the pressure rating indicated thereafter is Class 600 ； Or the design pressure is 2.0 MPa, or the maximum operating pressure is 2.0 MPa, or the maximum pressure difference is 2.0 MPa, with the pressure class indicated as Class 150 thereafter. So, I don’t know how to deal with this widespread problem. We invite all experts to participate actively.