Do normal pressure fixed roof tanks have to use weak connections?

Personally, I think weak connections are correct. In chemical plants, whether they are as large as a factory building or as small as bolts, there are generally some weak links. For example, the factory building must have an explosion venting wall to relieve pressure in time when an accident occurs. Bolts connected by bolts are harder than the nuts, so bolts that are easier to process should be set as wearing parts. Weak connections must be used for fixed roof tanks under normal pressure so that the pressure can be released in time when the system is overpressured. Compared with explosion and fire accidents caused by overpressure, environmental pollution and vapor cloud explosions are much less harmful.

I think the weak connection is correct. We need to consider two aspects when looking at the problem. As the poster said, after the explosion, the leakage port increases and the release volume increases. But on the other hand, when the foam is applied, more will be released, shortening the rescue time. The purpose of the weak connection is to let him open. Only in this way can the loss be reduced! Since it is a normal pressure tank, it would have already caught fire by the time it exploded! Will not cause secondary explosion damage

Dear colleagues: I have been confused about this issue for a long time. I think there is no need for weak connections and other methods can be used to relieve pressure. If an emergency blasting port is set on the top of the tank, the purpose of pressure relief can also be achieved as long as the calculation is correct. And because its area is much smaller than the channel area when the tank roof is lifted due to damage to the weak connection, it is better for safety and environmental protection than using weak connections. This is done in some foreign designs. But doing so violates our country's standards. From the perspective of compliance with laws and regulations, we have to wait for the adjustment of regulations. What we can do is discuss in depth and promote problem solving.

This post was last edited by zhenming178 on 2010-2-5 16:28. As we all know, steam cloud explosion requires conditions. It requires many conditions for the material to leak and float in the air to form a steam cloud. For example, the density of the material is small, the instantaneous leakage is large, the wind speed is small, and the space is small. Under these conditions, steam clouds are easily generated, and when the steam cloud is formed, there is an open flame before the explosion occurs. If there is an open flame when clouds are not forming, it is a pool fire. 1. Vapor cloud explosion is caused by the vapor cloud spreading in the form of "premixed cloud" exploding in a limited space after encountering fire. If the leaked oil does not explode with a boiling liquid expanding vapor cloud or immediately cause a fire, the low-boiling components of substances such as solvent oil or fuel oil will be fully mixed with air and gather in a certain range to form a premixed vapor cloud. If it is ignited by fire at a later time, since the gas-liquid two-phase material has been fully mixed with the air, the process once ignited is extremely violent, and the flame front speed can reach 50-100m/s, forming a deflagration. It will cause shock wave damage to buildings and equipment within the coverage of the vapor cloud, endangering people's lives. At least the following conditions should be met for a steam cloud explosion to occur:: ①The surrounding environment, such as trees, houses and other buildings, creates a certain restrictive space ； ②Delays the ignition process ； ③A fully premixed mixture of gas-liquid two-phase substances and air ； ④A certain amount of oil leaks. ----------------Excerpted from "Injury Model of Vapor Cloud Explosion" Will setting up weak connections in flammable and explosive substance storage tanks lead to the generation of steam clouds in the event of fire? If the tank is adjacent to the tank and is baked by flames, the tank is in danger of a steam cloud explosion. At this time, the storage tank should also be equipped with a fixed cooling device with a capacity of more than 500 cubic meters. According to petrochemical regulations, a foam fire extinguishing system should be installed, so whether a steam cloud explosion will occur depends on various prerequisites. Design fire protection specifications for petrochemical enterprises: Article 5.2.19 The connection between the fixed roof tank roof and the edge angle steel shall adopt a weak roof structure. No matter if a fixed-roof tank explodes, fires or boils for any reason, the top of the tank should be blown open first to ensure that the tank body is not damaged. Therefore, it is stipulated that any tank with a fixed roof should adopt a weak roof structure. ※The weak connection is to prevent the physical explosion of the container, and the emergency release is to process the materials in the tank. The emphasis is different.

This post was last posted by lyhh9024 on 2010-2-5 18:58 The editor personally supports weak connections. From the perspective of accidents, most atmospheric pressure tanks that bear pressure are caused by high-temperature baking or explosion fires in the tank. If a weak roof structure is not adopted, the tank is prone to bursting. At this time, the release amount of the medium in the tank is greater than the amount of medium released by the rupture of the weak roof, and the accident consequences caused by tank explosion are more serious than those caused by the rupture of the weak roof. From the perspective of environmental protection and reducing accident hazards, the weak roof structure is more reasonable.

I like this kind of discussion very much. Regardless of whether everyone's views can be unified now, I feel that I have been greatly inspired by your guidance. Thanks to Haichuan.com for providing us with such a platform, thanks to the host for vigorously advocating and organizing discussions, and thanks to colleagues for their enthusiastic participation and guidance. After the above discussion, I have considered some issues more deeply, and I have another question for you to ask.: What is the difference between explosion protection and overpressure protection devices?

According to Article 6.2.20 of GB50160-2008 Fire Protection Design Code for Petrochemical Enterprises, weak roof structures should be used when fixed roof tanks are used. According to Article 6.2.19, for fixed roof tanks of Class A, B, and B liquids sealed with nitrogen or other gases, accident pressure relief equipment, such as pressure relief manholes, breathing manholes, etc., shall be installed to ensure the safety of the tanks. In API650, there are specific diagrams for weak top structures.

The main purpose of the weak connection is that in the event of a fire or other unexpected situation, the internal pressure of the storage tank is overpressured, and the weak connection between the tank top and the tank wall is separated in time. At this time, the tank bottom and tank wall as a whole retain a safety margin and remain intact, preventing damage to the tank wall and tank bottom from causing a large amount of material leakage and causing greater accidents. Weak connections generally use unilateral welding, and the specific requirements are specifically stated in JB/T4735 and GB50341. Personally, I think the biggest difference between explosion protection and overpressure protection lies in the different principles and destructiveness. Overpressure does not necessarily lead to explosion, but explosion will generally result in overpressure. Overpressure protection facilities can include safety valves, breathing valves, bursting discs, etc. Explosion protection is divided into explosion prevention facilities or measures and post-explosion protective measures or facilities. The former has many facilities, such as liquid seals, water seals, flame arresters, etc. The measures include interlocks, emergency stops, various alarm systems, etc. The latter facilities include weak connections, explosion-proof walls, etc. Personal opinions, not necessarily correct, just for communication.

It is also difficult to reach a unified conclusion from the discussion. There's too much involved here. . .