Design And Optimization Of Weak Wall Protective Structure Of Fixed Roof Storage Tank

Storage tanks play a significant role in energy industry like storage and transportation of fossil fuel such as crude oil, natural gas and Petroleum gas. As the increasing consumption of energy because of the growing of our economy, huger storage tanks and more complex storage tank farms will be. It will probably cause serious consequences if such important devices have accidents. Thus, large proportion of scholars in the field of petrochemical engineering and safty engineering pay attention to the safty of oil storage tanks. As a result, a lot of technologies like breather valve, rupture disk and automatic temperature testing and warning system are being used on storage tanks now. These technologies and strategies did avoid some tragedies, but there are still quite a few oil storage tank catastrophes in recent year. What is worse, these calamities always happened with Domino Effect in tank farms which may lead to enormous damage in properties and casualties. It is recommended to use the weak roof structure in order to avoid the Domino Effect in tank farms and save more time for the first aid. But some of domestic researches imply that weak roof structure could not offer enough protection to the tank under some emergency circumstances since its own limit. So it is helpful to optimize the weak roof structure. The major work and conclusions are as follow:(1) The weak wall structure was proposed after the theoretical analysis and calculation. Four different sizes of weak wall storage tanks were designed and the welding line strength was tested through experiments. The results showed that the lower welding line height is the weaker welding line is.(2) Physical overpressure experiments were done with oil in DN 1000 weak wall storage tank. The results showed that, the tank was broken at weak wall structure when internal pressure reached 321 kPa. Bottom board swelled and uplifting effect happened. The average uplifting height was 35.1 mm. The experiment proved that the weak wall sturcuture did have weak link protecting effect.(3) Physical overpressure experiments were done with water in DN 3100 normal and weak wall storage tanks. Results of experiments showed that bottom boards swelled with the internal pressure increasing. The normal storage tank was broken at bottom welding line at the pressure of 78 kPa, and the average uplifting height of bottom rim is 175.25 mm. The weak wall storage tank was broken at weak wall welding line at the pressure of 70 kPa, and the average uplifting height of bottom rim is 151.6 mm. The experiment improved that the weak wall sturcuture did have weak link protecting effect.(4) Deflagration overpressure experiments were done with C2H2/AU" premixed gas in DN 500 normal and weak wall storage tanks. Results implied that, the pressure could reached 4.2 MPa in normal storage tank, but tank body was not broken. Weak wall storage tank was broken at weak wall structure and the highest pressure is 3.1 MPa. Weak wall with floating board storage tank was broken at weak wall structure as well, and the highest pressure is 3.5 MPa. So the floating board had no impact on weak wall protecting effect but can increase the overpressure.The result that weak wall storage tanks were all broken at weak wall structure showed that the weak wall structure had weak link protacting effect under deflagration overpressure.(5) The 3D finite element model of DN 1000 weak wall storage tank was established by ANSYS with units SOLID 185, CONTA 173, and TARGE 170. Base and gravity were considered.(6) The comparison of the experiments and simulation results reflected that the error on uplifting height was less than 8% and the average error on circumference strain at weak wall welding line was 6.43% which meaned that the finite element model was precise enough.(7) 3000 m3 finite element model was established based on the verified model to study the location and form of weak wall structure’s impact on weak wall protecting effect. Study showed that weak wall structure could change the maximum SINT location and improve its value. At the same time it increased the average value of SINT on the dangerous path.(8) The optimization of 3000 m3 storage tank and design principles showed that weak wall structure could change the stress distribution and mitigate the stress concentration at bottom welding line. It must be noted that only proper location of weak wall structure and appropriate height of welding line could ensure the weak wall protecting effect.