Safety Evaluation Research On The Foundation Uneven Settlement Of The Crude Oil Tank

With the rapid development of petrochemical industry in China, a large number ofstorage tanks of different capacity have been built. With the increase of operation time, partof the tank has uneven settlement. Once the uneven settlement accidents of tanks happen, itwill not only destroy the tank structure and foundation itself, but also lead to the interruptionof industrial production process. It will cause huge economic losses as well as considerableeffects on the environment. Therefore, through researching on the deformation law of storagetank foundation and its failure mechanism, the allowable settlement values of floating rooftanks with different volume under different uneven settlement types were determined. Thishas significant guide and reference value to practical engineering.This article took the floating tanks of5×104m3,10×104m3and15×104m3in Daqingoilfield as the research objects. Different loading conditions, boundary conditions andelement types were set. The finite element models of three volumes tanks under the conditionof planar inclined foundation, uneven settlement and the settlement difference between tankcenter and surrounding were established. The stress and displacement rules of tanks underdifferent uneven settlement types were analyzed.The deformation characteristic of tank is unevenness in the condition of planar inclinedfoundation. The max deformation occurs in middle-low part of floating roof tank. Themaximum stress and panel maximum displacement at the highest liquid level increases assubsidence value increases. The allowable settlement values of tanks of5×104m3,10×104m3and15×104m3under the condition of planar inclined foundation were0.30m,0.35m and0.38m. The finite element analysis results were greater than the allowable values set in thecurrent national standard GB50341-2003. The allowable values set in current nationalstandard for floating roof tanks under the condition of planar inclined foundation areconservative.The panel maximum displacement increases as subsidence value increases when thetanks under the condition of uneven settlement. The maximum displacement occurs at the topof the panel. The allowable settlement values of tanks of5×104m3,10×104m3and15×104m3under the condition of uneven settlement were27mm,30mm and32mm. The finite elementanalysis results were greater than the allowable values set in the current national standard GB50341-2003. The allowable values set in current national standard for floating roof tanksunder the condition of uneven settlement are conservative. The maximum stress in tank key parts increases as subsidence value increases when thetanks under the condition of the settlement difference between tank center and surrounding.The maximum stress appears at the junction between shell-to-bottom welds and tank bottom.Under the condition of the same settlement difference, the bigger the tank volume, the greaterthe stress of the key parts. The allowable settlement values of tanks of5×104m3,10×104m3and15×104m3under the condition of the settlement difference between tank center andsurrounding were3.0%,2.5%and2.2%. The finite element analysis results were within thescope set in the current national standard GB50341-2003. The allowable values set in currentnational standard for floating roof tanks under the condition of the settlement differencebetween tank center and surrounding are safe.