Research On The Safety Of Weak-roof Tank

In the petrochemical industry,the storage tanks contain volatile,inflammable and explosive materials.When these substances reach the explosion limit and meet the ignition source,they will cause fire and explosion,causing huge safety hazards and economic losses.Based on the defect that the accidental overpressure of fixed-roof tank can easily lead to the overall damage of tank,it is usually designed with a weak-roof structure.Its advantage is that the top position of the tank is lifted under unexpected overpressure,avoiding the risk of the overall damage of tank.However,the weak-roof tank in the accident was lifted off the bottom of the tank and did not lift as expected.In view of the short development history of weak-roof tank,the related research results are limited.It remains to be further studied whether the weak-roof tank has defects.Therefore,it is of great practical significance to study the safety of weak-roof tank.The main content and conclusion of this paper are as follows:(1)The accident tree analysis was carried out on the background of typical tank explosion accident.A total of 46 failure modes were found to cause tank explosion.According to the order of importance of accident tree structure,valve seal failure,flange seal failure,tank damage and misoperation are the main factors leading to tank explosion.(2)The factors influencing the failure position of the weak-roof tank under the condition of overpressure are the form of overpressure and the height of the reservoir.Under physical overpressure,the roof is broken.Under explosive overpressure,the damage position of tank is related to the height of the reservoir.When the height of the reservoir is not less than half of the highest level,the roof of the tank breaks;When the height of the reservoir is less than half of the highest level,the bottom of the tank breaks.(3)Under different liquid level,TNT equivalent method was used to quantitatively analyze the explosionconsequences of the vapor cloud of 5000m3 crude benzene tank at different liquid levels.The height of tank level is 1/2、2/3、3/4、4/5、5/6.The damage radius of the top and bottom of the tank caused by the expliosion of steam cloud was calculated respectively.The results show that the damage caused by roof rupture is closer to the minimum damage radius of each level than that caused by tank bottom rupture.(4)According to GB50341-2014《Design standard for vertical cylindrical steel welding tank》,based on TNT equivalent method,the relative value of shock wave overpressure at the weak position of tank at different liquid level is calculated.The results show that when the height of the reservoir is close to 3/4 of the full tank level,the overpressure value is the maximum.