Storage and Transportation Technology: [Weekly Topic] 10-11-26～28 How to repair roof tears in storage tanks?
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This post was last edited by flute6 on 2010-11-27 00:16. Dear colleagues, we have a vertical conical tank with a capacity of 1500 cubic meters in our tank area, which is used to store crude pyrolysis gasoline. A few days ago, due to the large amount of light components present in the crude pyrolysis gasoline coming from the unit area, and at that time the vent valve on the top of the tank was malfunctioning, this led to a crack that was over 6 meters long and 400 millimeters wide, forming at the junction where the top plate of the tank met its side plates. There are also multiple indentations around the crack; since it was caused by a tear in the top of the tank, what are the ways to repair it? Thank you! At the same time, I would like to discuss with everyone that both the deflation and overpressure of dome tanks are closely related to changes in the vapor pressure within those tanks. For tanks operating at atmospheric pressure, we usually set the tank pressure at plus or minus 50 millimeters of water column; in this case, the breather valve plays a crucial role. When the vapor pressure inside the tank falls below the set value, the suction valve of the breather valve activates, allowing outside air to enter the tank in order to maintain the desired slight positive pressure. Conversely, when the vapor pressure inside the tank is higher than the set value of the breathing valve, the vent valve of the breathing valve opens to release the excess gas from the tank, until the vapor pressure inside the tank reaches the set pressure of the breathing valve, at which point the vent valve closes. Therefore, the change in the vapor pressure of a dome tank is closely related to the material entering and leaving the tank, as well as changes in the temperature of the material inside the tank. In short, the integrity of the roof vent valve is key to ensuring the integrity of the dome tank. These are just my own thoughts; I hope colleagues can offer their feedback. Thank you! Note: There are rewards for participants in the discussion.
Use a transfer medium, correct the crack to its original state, then clean the edges of the crack and carry out butt welding. Then conduct the test
OP, I can tell you for sure that your design is incorrect. This storage tank cannot be used; replace it with a new one immediately. Your crude pyrolyzed gasoline should contain a high proportion of C5 compounds, including C5H10, whose saturated vapor pressure at 50°C is 0.09 MPa (g). There are also n-pentane (boiling point 36°C), isopentane (boiling point 28°C), and neopentane (boiling point 10°C). It’s incorrect to use a storage tank at atmospheric pressure without carrying out cracking; it’s fortunate that no explosion occurred despite the cracking. Take action to rectify this situation right away. Low-pressure spherical tanks, or low-pressure elliptical head tanks, must be used to fill with nitrogen. I hope the original poster will see my message as soon as possible. It’s too dangerous………………
Reply to 3# Storage and Transportation Engineer: Thank you for this suggestion. Our facility came online in 1996, and the three 1500-cubic-meter crude pyrolysis gasoline tanks have been in use to this day. Since starting operation, there has been an instance in which, due to an excessive amount of light components in the feed supplied to the front unit, the feed tank rose and ended up 400 millimeters above its base; however, the feed was stopped promptly, and the tank returned to its proper position. Just in the second half of this year, there were two instances of tank roof tears, and the management kept shirking responsibility; technically, they set the feeding height for the damaged tanks at 3.5 meters to 4.0 meters. Continue using it; for now, it seems there isn’t a very good solution for these two tanks.
This post was last edited and replied to by the Logistics Engineer on 2010-11-27 at 17:39. Reply to 4# LifeLove5907: Performing welding work in such an environment is practically asking for disaster. Its flash point is very low. Please don’t joke about the lives of workers. To carry out repairs, it is necessary to empty the tank to ensure that the conditions for working with fire are met. If everything is in order, the tank can be repaired successfully. Continue to use this type of tank. Here are some suggestions: 1. Apply thermal insulation coating to the outer surface; 2. Strictly control the temperature and pressure of the storage tank; 3. Activate the spray system to cool down the tank promptly in case of any abnormalities; 4. Set up a remote pressure monitoring room for real-time oversight. 5. Add emergency pressure relief manholes. 6. Control the feed liquid level
Although what the storage and transportation engineer said is not entirely correct, it still has some value as a reference. First, the poster needs to determine the parameters of the working medium (pressure, temperature, and composition) ； Secondly, when a large amount of high-pressure light components enter the tank, relying solely on a vent valve is too risky. Technically, it should be considered to install hydraulic safety valves and emergency pressure relief caps to provide multiple layers of protection. Finally, if it is possible to add some detection methods, it would allow for rapid and timely monitoring of feed parameters and forecasting of operating conditions. I have no experience in repairing tank roofs; I look forward to hearing about your experiences once you are successful.
This post was last edited and replied to by the Logistics Engineer on 2010-11-30 at 15:41. Reply to 6# qdfox to discuss this issue with you. I don’t know where I went wrong I earnestly request your guidance. It should be noted that there are two words in his question: first, \"coarse cracking,\" and second, \"light components.\" From these two words, it can be inferred that this oil is a light-component oil. Therefore, atmospheric pressure tanks cannot be used. I see you’re still using a normal-pressure tank; I don’t quite understand it. I would appreciate your advice. PS: Other people have also tried this design used by the original poster, and problems have occurred as well. The reason is actually very simple. A little analysis will suffice.
According to the specifications, internal floating roof tanks should be used for storing gasoline. However, the situation described by the poster is certainly not suitable; as an intermediate tank in the plant (for crude pyrolyzed gasoline), the flow of material in and out of this tank is very unstable. When the plant is not operating properly, a large amount of light components end up being carried into the tank, and it may not be possible to exchange heat before they reach the tank, resulting in a sharp increase in the gas phase inside the tank. The breather valve installed on the tank is not sufficient to handle this situation, leading to an increase in pressure inside the tank and eventually causing the tank to rupture； Furthermore, due to the high proportion of light components, it is highly sensitive to ambient temperature; the rapid condensation in the gas phase prevents the breather valve from meeting the inhalation requirements, resulting in the tank collapsing. To meet the requirements of the plant’s production process, it may not be possible to change the design of this storage tank. Therefore, efforts should be made in terms of operational management and safety measures, and coordination with the plant is necessary (to minimize any impact on the tank). What everyone has said makes sense; it is recommended to increase the breathing capacity of the tank’s vent valves or to add more of them, as well as to install safety pressure relief vents on the top of the tank. From an environmental protection perspective, the exhaust pressure of the breather valve should be increased appropriately.
Regarding atmospheric pressure tanks, when there is a high proportion of light components, nitrogen shielding is required; in addition, breathing vents equipped with flame arrestors should be installed, along with automatic breathing valves； For the repair of atmospheric pressure tank roofs, the most reliable method is replacement and welding; as a temporary solution, resin mesh frameworks can be used for reinforcement.
Our workshop has 3 atmospheric-pressure storage tanks with a capacity of 3,000 m3 each, which are used for storing acrylonitrile. In addition to the breather valves that ensure proper functioning, there are also two overflow holes on the top of the tanks for emergency pressure relief. Moreover, nitrogen purging is necessary inside the tanks, with automatic control valves regulating this process in order to maintain stable pressure within the tanks and prevent them from expanding or collapsing. Recommendation: Regularly check the breather valve of the storage tank to ensure it operates smoothly. (We once experienced rusting of the breathing valve due to moisture issues, which prevented it from functioning properly and led to overpressure in the storage tank; however, this was detected and resolved in a timely manner.) Regardless of how the storage tank is repaired, it must be emptied and refilled.
Judging from the poster’s description, the scene there was truly breathtaking! Tear in the tank top, the feed tank lifting off…… Such accidents have occurred multiple times, and yet they still consider repairing the tank and continuing to use it – that’s quite irresponsible, isn’t it? Monitoring and management can only prevent problems from arising temporarily. Such problems must be completely resolved.