Can the floating disk of a nitrogen-sealed floating roof tank sink to the bottom?
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I’ve seen discussions on this topic in the community, and I searched Baidu for information on the management of internal floating roofs; most of the content referred to oil and gas tanks, without providing specific guidance on how to handle bottoming out in nitrogen-sealed internal floating roof tanks. **Article 6 of the Ten Provisions on Fire and Explosion Prevention in Oil and Gas Tank Farms, as issued by the State Administration of Work Safety (Order No. 84), stipulates as follows: 6. It is strictly prohibited for the floating roof of an internal floating roof storage tank to drop to the bottom while the tank is in operation. This article mainly specifies the requirements for the liquid level in internal floating roof storage tanks. The float falling to the bottom refers to the situation where, due to an excessively low liquid level in the tank, the float settles on the support legs. During normal operation, once the floating disk settles at the bottom, a gas space is formed between the disk and the oil surface. When the flow rate of the material is too high, static electricity tends to accumulate at the outlet of the material pipeline, which can very easily lead to fires and explosions. Typical accident case: On August 29, 2011, an explosion and fire occurred in a diesel tank at CNPC Dalian Petrochemical. The main cause of the accident was the low liquid level resulting from oil being supplied to the tank; this created a gas space between the floating disk and the surface of the diesel, allowing air to enter ； At the same time, fluctuations in the operation of the upstream units led to an increase in the content of light components in the diesel that entered the accident storage tank, resulting in the formation of an explosive mixture beneath the floating disk ； Furthermore, the rapid flow rate of the incoming oil generates a large amount of static electricity that cannot be discharged in time, leading to discharges and subsequent explosions and fires. There’s no need to worry at all for us; the tank contains flammable and explosive hazardous chemicals, and it is sealed with nitrogen – with a nitrogen content of over 99%. There is no gas space present, and the pumps used for transferring materials in and out are designed with considerations for static electricity issues, so they won’t operate too quickly. Some experts came for an inspection and said that it couldn’t be placed on the bottom; this is part of the regulations. They also said that regular inspections of the floating platform are necessary (I really want to scold them – I’ve already sealed it with nitrogen, yet during the inspection I still have to empty the contents, remove the access panels, and fill it with oxygen, which creates additional safety risks). Other experts, however, understood the situation and said there shouldn’t be any problems. Let’s discuss whether this can actually be implemented, and whether there are any relevant regulations.
It’s not possible under normal circumstances. Unless you empty the tank, be careful to protect it.
The last edit to this post was made by yu*nyang_01 on 2019-12-10 at 22:01. Is the statement \"Nitrogen sealing for hazardous material storage tanks, with a nitrogen concentration of over 99%, resulting in no gas phase space\" incorrect? The internal floating roof nitrogen seal is installed on top of the floating disk; when the floating disk settles to the bottom, a gas space is formed below. – Sorry, I misunderstood; this gas space might be a non-explosive mixture
What I mean is that for explosive mixtures, there must be a gas phase space.
I understand Document No. 84: During normal operation, when the floating disk settles at the bottom, an air space is formed between the floating disk and the oil surface. When the flow rate of the material is too high, static electricity tends to accumulate at the outlet of the material pipeline, which can very easily lead to fires and explosions. The space mentioned here refers to explosive mixtures, which are certainly those materials within their explosive limit range. Since nitrogen sealing has already been done to prevent the formation of explosive substances and to avoid situations within the explosion range, is it still necessary to take measures to prevent things from falling to the bottom? !
The internal floating roof nitrogen seal is applied on top of the floating disk; when the floating disk settles to the bottom, a gas space is formed below
Apart from modifying the tank, it’s not allowed under normal circumstances
In ordinary internal floating disk storage tanks, the use of an internal floating disk is generally not allowed; as you know, there’s no need for further explanation. You have a nitrogen seal, so it’s safe, but what if something goes wrong and you end up causing the floating platform to land? Someone will have to take responsibility in such a case, right? The safety regulations don’t state that in tanks with nitrogen sealing, the floating disk can be lowered as long as everything is fine – right? There is only a rule against operating at low liquid levels, regardless of whether there is a nitrogen seal or not. So, don’t operate at low liquid levels when everything is fine; otherwise, you’ll be in trouble if something goes wrong.
It’s better to do less than to do more; it’s best if nothing happens at all. However, in actual production, considerations regarding inventory levels often lead to difficulties, especially in the tank areas at ports, where leasing is particularly easy.
There is definitely a gas phase space, but it contains no oxygen, so there is no risk of explosion.
In a nitrogen-sealed storage tank, nitrogen is present at the top under normal conditions. When material is discharged, nitrogen cannot be replenished in time, so the breather valve draws in air. Once the floating disk drops to the bottom, air may exist in the gas space below the floating disk