1. Risk Analysis of Large Crude Oil Storage Tank Project
1.1 Crude oil hazard analysis
The crude oil is Class A and B flammable liquid, with flammability; The explosion limit range is narrow, but the value is low, which has a certain explosion risk. At the same time, the boiling overflow of crude oil should be paid special attention in fire fighting.
1.2 Cause analysis of fire and explosion accidents
The characteristics of crude oil determine that fire and explosion risk is the most important and the most important risk factor for large crude oil tanks. The three necessary conditions for fire accidents are: ignition source, combustibles 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 tank design.
The leaked crude oil is exposed to the air, which constitutes combustibles. Crude oil leakage occurs frequently during storage and transportation, mainly including oil leakage from the tank, dehydration, equipment, pipeline and valve damage, and oil and gas volatilization due to poor sealing. In addition, there are also the possibility of large leakage accidents such as tank bottom cracking and floating plate sinking.
Corrosion is one of the important factors for leakage. Oil leakage accidents caused by corrosion of oil tank bottom have occurred at home and abroad. The preliminary investigation on the internal corrosion of crude oil storage tank shows that [1], the tank bottom corrosion is serious, mostly ulcer like pitting corrosion, mainly occurring in the welding heat affected zone, depression and deformation, followed by the tank top corrosion, which is uneven overall corrosion accompanied by pitting corrosion, and the tank wall corrosion is relatively mild, which is uniform pitting corrosion, mainly occurring at the oil-water interface, oil and air interface. Relatively speaking, the external corrosion of the tank bottom is more serious, mainly on the side where the edge plate contacts the ring beam foundation.
The accident of floating plate sinking is one of the serious equipment accidents that are very taboo in the production and operation of floating roof oil tanks. The occurrence of such accidents, on the one hand, reflects the serious defects in design, construction and management, on the other hand, will cause a large number of crude oil leakage, seriously affect production, pollute the environment and constitute a fire hazard.
2 Main Safety Problems and Countermeasures in the Design of Large Crude Oil Storage Tanks
2.1 Tank foundation and foundation
Tank foundation survey and tank foundation design are the most fundamental guarantee to ensure the safe operation of large tanks. According to the petrochemical industry standard [2], engineering geological investigation must be carried out in the process of project site selection. For the general foundation, soft soil foundation, mountain foundation and special soil foundation, the corresponding foundation treatment methods shall be proposed based on the verified conditions. At the same time, the seismic effect evaluation of the site and foundation shall be conducted to avoid building on the foundation with different soft and hard or within the influence range of active geological fault zone.
Common tank foundation forms include ring wall (beam) type, outer ring wall (beam) type and slope protection type. The selection shall be based on geological conditions. The tank foundation must have sufficient overall stability, uniformity and sufficient plane bending stiffness. The stiffness 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. Waterproof oil barrier and oil leakage signal pipe should be set. The distance between the groundwater level and the top surface of the foundation should not be less than the height that the capillary water can reach (generally 2m)