Problem of natural pressure buildup in closed material pipelines?
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Recently, a certain section of the pipeline in our facility has been experiencing gradual pressure buildup. The pressure increases over time once pumping of the material stops; it can rise to 0.6 MPa within an hour. External influences have been ruled out, and the pressure continues to increase over time even after pressure release. The issue is more severe during the day and less so at night. I suspect it might be related to temperature – am I correct? There is a temperature difference of around 15-20°C between the temperature of the material and the ambient temperature; the pipelines lack insulation. I would like to know if anyone has encountered similar problems and how they were resolved
It gets severe during the day and milder at night; it’s likely caused by rising temperatures
Personally, I think too rapid pressure increase may indicate slight internal leakage in the valves. Of course, the pressure also rises quickly during the day when temperatures are higher, but it should decrease at night. In a situation where both valves at the ends of such a pipe are closed, one valve needs to be opened to relieve pressure; since the valve at the other end is closed, the fluid will not flow back. If the valve cannot be opened, the drain valve can be opened during the hottest part of the day to relieve pressure, and then closed again.
We have encountered such a problem before； (I’m not sure if it’s the same for you), the main reason is that after delivery, the pipeline is filled with liquid, creating a liquid seal; when the temperature changes, thermal expansion occurs, which leads to an increase in pressure (which can be quite high). As a result, the safety valves on our pipelines have activated several times. The approach we initially took was to drain some of the liquid from the pipeline after delivery, thereby creating space inside it ； As the temperature rises, the maximum pressure in the pipeline is the saturated vapor pressure of the liquid at that temperature ； Finally, we adopt a solution that links pressure to the valve; when the pressure reaches a certain level, the valve opens to allow pressure release ；
This kind of situation is very likely to occur with thermosensitive substances. I don’t know what kind of person the original poster is. Can a valve be opened on a pressurized pipeline to lead into a container and left open at all times for pressure relief? Depending on the type of pump, is it possible to open the pump outlet valve to allow the material to flow back into the container?
I remember there was a specification requiring pressure relief measures to prevent overpressure in the sealed sections of pipes.
Our material is xylene. There is no suitable vent point on the pipeline, but it is possible to open the container’s discharge valve for a short period of time to relieve pressure, provided that the container is not in use. Could you provide the coefficient of thermal expansion for xylene at different temperatures? Can it be calculated? It is generally believed that such high pressure cannot be generated
Thank you! Let me check if there are any relevant specifications!
Yes, the situation of the poster is somewhat similar to ours, but I’m not sure how large the temperature variations are you’re talking about. In my container, the temperature is around 25°C, while the ambient temperature is around 40°C. Additionally, our pipeline design isn’t very thorough – there are no appropriate pressure relief vents (this needs to be improved, haha!) ), if it’s that problem, should it get better or disappear during winter?
I don’t have the data on the related materials； If the ambient temperature is higher than the temperature of the material, a similar situation may occur when the pipeline is filled with the material ； It’s better when the ambient temperature is low ； It might rise a bit more slowly ； Is there a process flow diagram? (We have taken such situations into account in the design of some of our pipelines.) ； For example, after some automatic valves are closed, there is actually a 5% opening degree ；
I am very grateful for your continuous support. After consulting with the factory’s technical staff and relevant managers, we plan to keep the discharge valve of one of the containers open after pumping, closing it only before use, and repeating this process. We are currently adjusting the DCS system programs in hopes that this will help alleviate the issue. I will share the results of the subsequent tests with everyone!