Strange signs in the pipeline—rising pressure
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Our company has the same system for storing and pumping diethylene glycol, as shown in the process diagram. Located in Guangdong, the temperature difference or overall temperature is not high. In the production mode, the bottom valve of the storage tank is open, the DN40 discharge valve at the top of the tank is closed (the DN25 pressure regulating valve is set to a certain opening degree), the discharge valve remains in the closed position, the manual ball valve for feeding (DN40PN16) is open, and XV220 is also open to allow material feeding. In the shutdown state, the pump is stopped, the bottom valve is closed, the feed ball valve (DN40PN16, i.e., at the location of the red gasket) is closed, and XV220 is also closed. These steps were followed before work ended on Saturday; upon starting work on Monday, a leak was detected at the location of the red gasket (the removed gasket is shown in the image). This issue persisted, and at one point the gasket was even torn in half (the new gasket that was installed was broken in half as well), causing the material to spray out up to 6 meters away. The pipe material is 304, and piping is installed in accordance with industry standards. The gasket is made of polytetrafluoroethylene; it can be folded by hand and possesses excellent toughness. May I ask: does diethylene glycol (DEG) undergo self-decomposition? Or what factors cause the pressure of diethylene glycol to rise sharply in a sealed space? Thank you!
The gasket is too soft. Replace it with a PTFE composite gasket, that is, an asbestos gasket with a PTFE outer layer.
The pressure should vary. Look for the process reason for the change. We will solve the gasket problem. The pressure is not high, so the leakage can be fixed
The pressure is way too high. May I ask what the flow rate of this pump is?
This material has cold flow properties and deforms under heavy stress. Therefore, it is generally used for low pressures, or the flanges should have male and female surfaces, preferably tenon-and-socket types. Replacing it with a PTFE-reinforced or composite gasket solves the problem. The increase in pressure may be due to the vaporization of the medium in the enclosed space between the two valves, which raises the pressure. From an equipment perspective, adding a bypass to allow for timely discharge of this vapor should suffice. However, the process needs to be determined based on the safety of the medium.
1. What is the temperature of the storage tank and the ambient temperature? Could an increase in the temperature of the material inside the pipes after shutdown lead to a rise in pressure? 2. Is there heating provided for the pipeline during line changes? If the heating remains active after shutdown, it can cause pressure to rise, resulting in leakage of the material from weak points. 3. Once it is confirmed that pressure buildup is the cause, it is necessary to ensure that there are ways to release pressure from the pipelines
I think it’s still a matter of temperature differences; even in Guangdong, there are day-and-night temperature variations. Moreover, since this gasket is located behind the check valve, any increase in pressure elsewhere is transmitted to this area. The XV-220 at the back door is also in a closed state, so this is the only weak point. At the same time, the check function of this check valve is excellent.....
I think the reasons are as follows: 1. It is mainly related to the fact that the pressure relief process is not functioning properly, and the material in the main pipeline has not been discharged or cleaned thoroughly in a timely manner. 2. The gasket selected was also inappropriate. 3. There are no reliable means for pressure monitoring. Solutions: Liquid can be appropriately drained from the low-point drain location behind the ball valve to reduce the pressure in the pipeline; 2. If possible, the main unit can also be used to relieve pressure, by opening XV220; 3. Alternatively, this section of the pipeline can be purged with nitrogen.
The check valve is in the wrong position; there is no possibility of pressure relief in the pipe section leading from the check valve to the workshop. Changes in temperature differences, as well as other factors, prevent pressure relief. I remember that generally, the check valve is located after the pump, with various pipelines following thereafter；