Discussion on the cross-sectional area of the collection main pipe for the vent pipes behind the explosion-proof membranes of multiple containers!
Thread Content
This post was last edited by yu_er_2009 on 2020-4-28 at 15:31. Currently, as chemical enterprises in Yancheng City resume operations, experts have proposed the following corrective measures: Since the media inside the reaction vessels are flammable or toxic substances, the discharge pipes connected to the explosion-proof membranes of these vessels need to be linked to a collection tank for the discharged materials. In most cases, enterprises connect the discharge pipes from the explosion-proof membranes of reaction vessels with similar properties together through a single main pipe, which is then connected to the collection tank. The practice adopted by these enterprises is to ensure that the cross-sectional area of the main pipe is equal to that of the individual branch pipes. However, experts believe that the cross-sectional area of the main pipe should equal the sum of the cross-sectional areas of all the branch pipes. Therefore, they have requested that enterprises make the necessary corrections. Please share your opinions on this issue – are the experts’ requirements correct? My understanding is as follows: 1. The design is based on the water flow rate of outdoor fire hydrants. When there are multiple buildings in the vicinity, it is generally assumed that in the event of a fire (not simultaneous fires in multiple buildings), the building that requires the most water for firefighting will determine the design flow rate for the outdoor hydrants in that area. By the same logic, for multiple containers (without considering simultaneous explosions), the cross-sectional area of the main discharge pipe should be determined using the largest diameter of any individual discharge pipe ； 2. Referring to B10.1 in GB150.1–2011 Pressure Vessels – Part 1: General Requirements, as shown in the figure below, it is clear that the experts interpreted the multiple relief devices mentioned here as multiple vessels; in reality, these relief devices should be safety valves and explosion-proof membranes. 3. Additionally, according to GB 567.2–2012, Safety Devices for Pressure Relief Valves – Part 2, 6.1.2.3, my understanding is that when two or more pressure relief valves are installed on a single pressure-bearing device and discharge pipes are used to connect them, the cross-sectional area of these collection pipes should equal the sum of the cross-sectional areas of the individual branch pipes. Please feel free to discuss whether my understanding above is correct, and let’s learn together. Thank you!
The experts are correct; even for two safety valves installed on the same pressure vessel, the combined diameter of their discharge pipes should be no smaller than the sum of the cross-sectional areas of the discharge pipes of the two safety valves. The fact that you are using such practices on site indicates that no proper design has been carried out; a design review is necessary.
It’s not that complicated; regardless of whether there is one or two containers, if the rupture discs might explode simultaneously, then the total pipe diameter needs to be taken into consideration; if they don’t explode at the same time, then it’s not necessary to consider it.
It is correct that the combined pipe for the safety valves of two pressure vessels should have an area no smaller than the sum of the discharge pipe areas of the two safety valves; what I want to say is regarding the combined pipe for the discharge pipes of the safety devices of two pressure vessels
The experts’ understanding is incorrect. In safety design, it is generally not considered that two accidents could occur at the same time.
This post was last edited by liuhonglan on 2020-4-28 at 19:22. Like! ! !
Our company has made the changes as requested by those experts – the diameter of the main pipe has been increased to 400, which is insane. It’s clear that this represents a misinterpretation of the standards, but we still have to follow their instructions. Those officials from the Emergency Management Bureau are all idiots! OP, you guys had better change it
Experts clearly have a misunderstanding of the standards; it’s impossible for multiple containers to explode simultaneously. I support the original poster’s view!
At 18:42:33 on July 12, 2018, a severe explosion and fire broke out at Yibin Hengda Technology Co., Ltd., located in the Yangchun Industrial Park in Jiang’an County, Yibin City. The incident resulted in 19 deaths and 12 injuries, with direct economic losses amounting to over 41.42 million yuan. The direct cause of the accident was that the operator mistook sodium chlorate, which had no packaging label, for butyramide and added it to Reactor 2R301 in Workshop 2 for dehydration operations, resulting in an explosion and fire. In this accident, an error in material feeding caused the reaction vessel to overpressurize, leading to an explosion and fire. Is it possible for two or more devices to experience feeding errors or operational mistakes at the same time, resulting in overpressure and thus the activation of safety valves or the rupture of burst discs? Is it possible for overpressure to occur simultaneously in consecutive processing steps due to the connection between pipes? If two or more devices experience overpressure simultaneously, but the area of the relief piping is insufficient, could this lead to a more serious accident? Therefore, it is not possible to discuss this using \"general circumstances\"; instead, a comprehensive Hazard and Operability Study \"HAZOP\" should be conducted to provide evidence. The “safety relief device” that the original poster specifically emphasized refers to a safety valve or a burst disc, not multiple containers; so do multiple containers have multiple safety relief devices? The answer is yes. So, my understanding is: when the safety relief devices of two or more containers are connected to a main pipe, the cross-sectional area of the main pipe should be greater than the sum of the cross-sectional areas of those safety relief devices ； For multiple safety relief devices in the same container, the cross-sectional area of the main pipe should also be greater than the sum of the cross-sectional areas of those safety relief devices, in order to ensure their effectiveness!
This post was last edited by yu_er_2009 on 2020-4-29 at 12:41. First of all, many thanks to the person on floor 10 for their active participation and in-depth discussions! Above, a serious safety accident that occurred at a company in the Jiang’an County Industrial Park in Yibin was mentioned, caused by incorrect material being fed into one of the reactors. This leads to the possibility that multiple devices could experience incorrect material feeding at the same time, resulting in two or more devices experiencing overpressure, with safety valves activating or rupture disks breaking. Therefore, when the safety relief devices of two or more containers are connected to a main pipe, the cross-sectional area of that main pipe should be larger than the sum of the cross-sectional areas of those relief devices. At first glance, this analysis seems reasonable; it is possible for multiple devices to release pressure simultaneously, and this scenario does exist statistically. However, if we think further about it, we realize that if two or more devices in that factory are likely to experience overpressure, then it is possible that all devices in that factory could have accidents at the same time. Extending this logic further, it is possible that all devices in the entire industrial park could have accidents simultaneously, and so on... Here, we are only talking about possibilities, meaning that such scenarios do exist statistically. But in reality, I believe that thinking in this way is clearly incorrect; we cannot consider things in this manner during design. In terms of design, for a single device, we need to conduct analyses and calculations based on the materials contained within the device as well as the operating conditions, in order to determine the explosion venting area under extreme conditions. If multiple venting devices are installed, it is assumed that they all vent simultaneously; therefore, the total venting area for a single device is the sum of the areas of all the safety venting devices installed. When discharge collection pipes are used for multiple venting devices on one device, the cross-sectional area of such collection pipe is equal to the sum of the cross-sectional areas of the individual pipes. In the design of multiple devices, however, this low-probability scenario of all devices venting at the same time is not taken into consideration.