Issues related to the installation of shut-off valves for control valves in hydrogen-rich two-phase fluids under high pressure; details are provided in the main text
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The process conditions include a pressure of 12.1 MPa and temperatures ranging from 45 to 260°C; the medium is a two-phase fluid rich in hydrogen. As shown in the figure: To enable maintenance without shutting down the system, isolation valves are installed before and after the control valve as well as before and after the flow meter, along with corresponding bypass valves. The process purchaser first raised questions regarding the process valve assembly: should dual isolation valves be installed before and after the control valve? ? I checked the information I have available, but couldn’t find any relevant standards. Now I would like to ask: in the situation I described, how many sets of control valves, flow meters, and shut-off valves should be installed upstream and downstream of the control valve? Or are there any better design approaches to carry out maintenance on the control valve flow meter without stopping operation (under the aforementioned process conditions)?
In the high-pressure section, due to the large number of valve assemblies, installing dual valves would result in significant additional costs. Therefore, the process procurement party has requested specific proposals regarding the necessity and quantity of auxiliary valves before and after the control valve assemblies. In line with the process requirements, it is now essential that the control valves be equipped with mechanisms that allow for maintenance without shutting down operations. If anyone has better design ideas, I would appreciate it if they could recommend them
If only investment costs are considered, the double-valve assembly in the bypass can be replaced with a single-valve assembly; however, the potential for leakage within the bypass during normal operation must be taken into account, given that the operating pressure is 12 MPa. At present, without affecting normal production, setting up a bypass is a good option for maintaining flow meters and control valves. For chemical manufacturing enterprises, safety should take precedence over investment costs alone.
Well, for the inlet and outlet shut-off valves, should they be set up as a pair of valves? After all, offline maintenance of control valves poses significant risks. At present, if a pair of valves are to be used, specific standards need to be established. I checked the relevant national standards available to me, but none of them seem suitable for this purpose. From a rigorous chemical engineering perspective, it is necessary to find the corresponding standard for each item.
Based on my work experience, installing valve banks before and after the flowmeter and control valves respectively to facilitate offline maintenance is a commonly used and practical approach at present. But to give a reason based on standards, I’m not in design, so I can’t provide you with an exact answer. It is recommended that you get in touch and communicate with the design firm.