1 Hazard analysis of large crude oil storage tank engineering
1.1 Risk analysis of crude oil
Crude oil is a Class A and B flammable liquid, which is flammable; the explosion limit range is narrow, but the value is low, and it has a certain explosion hazard. At the same time, the boiling and overflow of crude oil should be paid special attention to during fire fighting.
1.2 Analysis of the causes of fire and explosion accidents
The characteristics of crude oil determine the risk of fire and explosion, which is the most important and most important risk factor for large crude oil storage tanks. The three necessary conditions for a fire accident are: ignition source, combustible material and air.
The problem of ignition source is mainly solved by strengthening management, and the problem of combustible leakage must be prevented and controlled in the process of storage tank design.
The leaked crude oil becomes combustible when exposed to the air. Crude oil leakage occurs frequently during storage and transportation. It mainly includes oil spilling from tanks, oil running from dehydration, damage to equipment, pipelines, and valves, and oil and gas volatilization caused by poor sealing. In addition, there are also open welding cracks at the bottom of the tank and sinking of floating disks. The possibility of large-scale leakage accidents such as the bottom.
Corrosion is one of the important factors for leakage. There have been many oil spills caused by corrosion at the bottom of oil tanks at home and abroad. The results of preliminary investigation of the corrosion in crude oil storage tanks show that [1], the corrosion of the tank bottom is serious, most of which are ulcer-like pit corrosion, which mainly occurs in welding heat-affected areas, depressions and deformations, followed by tank top corrosion. It is the uneven overall corrosion accompanied by pitting corrosion, and the tank wall corrosion is relatively light, and it is uniform pitting corrosion, which mainly occurs at the oil-water interface and the oil-air interface. Relatively speaking, the external corrosion at the bottom of the storage tank is more serious, which mainly occurs on the side where the edge plate is in contact with the ring beam foundation.
The sinking of the floating pan is one of the serious malignant equipment accidents that are taboo during the production of floating roof oil tanks. The occurrence of this type of accidents, on the one hand, reflects serious deficiencies in design, construction, and management, on the other hand, it will cause a large amount of crude oil to leak, which will seriously affect production, pollute the environment and pose a fire hazard.
2 Main safety issues and countermeasures in the design of large crude oil storage tanks
2.1 Foundation and foundation of storage tank
The foundation survey of the storage tank project and the design of the tank foundation are the most fundamental guarantees to ensure the safe operation of large storage tanks. According to the petrochemical industry standard [2], engineering geological surveys must be carried out in the process of project site selection. For general foundations, soft soil foundations, mountainous foundations and special soil foundations, the conditions should be investigated separately, and corresponding foundation treatment methods should be proposed. The seismic effect of the site and foundation should be evaluated, and it should be avoided to build on soft and hard foundations or within the influence range of active geological fault zones.
Common tank foundation forms include ring wall (beam) type, outer ring wall (beam) type and slope protection type. The selection should be made according to geological conditions. The tank foundation must have sufficient overall stability, uniformity and sufficient plane flexural rigidity. The rigidity of the foundation structure directly below the tank wall should be strengthened. The foundation bed supporting the bottom plate should be flexible to absorb welding deformation, and waterproof partitions should be provided. The distance between the oil layer and the oil spill signal pipe, the groundwater level and the top surface of the foundation shall not be less than the height that the capillary water can reach (generally 2m) [3].