Roof Tanks Research Articles

Research on spark discharge of floating roof tank shunt

In order to quantitatively analyze the spark discharge risk of floating roof tank shunts, the breakdown voltage of shunt has been calculated by Townsend theory, the shunt spark discharge experiment is carried out by using 1.2/50 μs impulse voltage wave, and the relationship between breakdown voltage of shunt spark discharge and air gap is analyzed. It has been indicated by theoretical analysis and experimental study that the small gap is more easily cause spark discharge than the big gap when the contact between shunt and tank shell is poor. When air gap distance is equal to 0.1 cm, average breakdown voltage is 5280 V. When the air gap distance is less than 0.3 cm, experiment data agree well with Townsend theory. Therefore, in the condition of small gap, Townsend theory can be used to calculated breakdown voltage of shunt. Finally, based on the above conclusions, improvements for avoiding the spark discharge risk of shunt of floating roof tanks have been proposed.

Estimation of evaporative losses during storage of crude oil and petroleum products

Storage of crude oil and petroleum products inevitably leads to evaporative losses. Those losses are important for the industrial plants mass balances, as well as for the environmental protection. In this paper, estimation of evaporative losses was performed using software program TANKS 409d which was developed by the Agency for Environmental Protection of the United States - US EPA. Emissions were estimated for the following types of storage tanks: fixed conical roof tank, fixed dome roof tank, external floating roof tank, internal floating roof tank and domed external floating roof tank. Obtained results show quantities of evaporated losses per tone of stored liquid. Crude oil fixed roof storage tank losses are cca 0.5 kg per tone of crude oil. For floating roof, crude oil losses are 0.001 kg/t. Fuel oil (diesel fuel and heating oil) have the smallest evaporation losses, which are in order of magnitude 10-3 kg/tone. Liquids with higher Reid Vapour Pressure have very high evaporative losses for tanks with fixed roof, up to 2.07 kg/tone. In case of external floating roof tank, losses are 0.32 kg/tone. The smallest losses are for internal floating roof tank and domed external floating roof tank: 0.072 and 0.044, respectively. Finally, it can be concluded that the liquid with low volatility of low BTEX amount can be stored in tanks with fixed roof. In this case, the prevailing economic aspect, because the total amount of evaporative loss does not significantly affect the environment. On the other hand, storage of volatile derivatives with high levels of BTEX is not justified from the economic point of view or from the standpoint of the environment protection.

Buckling analysis of open top tanks subjected to harmonic settlement

This work addresses the buckling behavior of the open top tanks subjected to harmonic settlement. First of all, the buckling behavior and the critical harmonic settlement of an open top tank for various wave numbers are investigated. The results present that buckling occurs on the upper shell for a small wave number, while it changes to other places of the shell for large wave numbers. Also, with the wave number increasing, the buckling point is closer to the base of the shell. Besides, for the original tank, the critical harmonic settlement decreases greatly when the wave number is small, while the critical harmonic settlement decreases slightly when the wave number is large. Then, the parametric studies for the buckling behavior of the open top tank are conducted, composed of the height-to-radius (h/r) ratio and the radius-to-thickness (r/t) ratio. Regarding the h/r ratio, for a certain wave number, the critical harmonic settlement versus the h/r ratio is monotonically decreasing. Also, with the wave number increasing, the critical harmonic settlement decreases more and more slightly. Regarding the r/t ratio, for a certain wave number, the critical harmonic settlement versus the r/t ratio is monotonically decreasing. Moreover, with the increasing wave number, the critical harmonic settlement decreases more and more slightly. Finally, the buckling results of the open top tank are compared with that of the conical roof tank. The results illustrate that the open top tank can hold a larger harmonic settlement than the conical roof tank for no restraint from the roof for a small wave number. However, for large wave numbers, there is a small difference in settlement sustaining capacity for open top tanks and conical roof tanks.

Determination of leakage inside buildings with a roof tank

Buildings with a roof tank are common in countries with intermittent water supply. For these buildings, it is difficult to determine the leaks inside with the methods developed for pressurised networks of drinking water. A proposed alternative is Continuous Automatic Tank Gauging. Although commonly used to check the tightness of gasoline storage tanks, this method still has not been used to determine water leaks. This study explains how to set up the method and shows its application to six buildings. As expected, the leak magnitude was found to increase with the size and age of buildings. In practice, the method can estimate (within ± 30%) a leak as small as 1 l/h in buildings with a small roof tank and 20 l/h in buildings with a large roof tank.

Analysis and Control of Double Sealing Space Discharge in Floating Roof Tank

The double seals technology is widely used in the large oil tank. But several oil tank lightning fire accident investigations illustrate that fires were caused by the discharge in the double sealing space. In this paper, the mechanism of lightning fire accident in the double sealing space was analyzed based on the investigation results of some domestic lightning accidents of large floating roof tanks. The lightning protection measures for floating roof tank’s second sealing space was summarized including both domestic and foreign lightning protection related codes, specification specifications and technology technologies.

Research of wind and snow cover loads on the roofs of the vertical cylindrical tanks

Research of wind and snow cover loads on the roofs of the vertical cylindrical tanks

Analysis and experimental investigation of direct lightning protection for floating roof oil tanks

To improve the lightning protection of large floating roof oil tanks, the process of floating roof tanks stroked by lightning is analyzed, and relevant tests have been developed according to standards. Test results indicate that the major role of conductive film is to release lightning current rapidly, but the presence of conductive films has counter-effects. As long as conductive film is present, it will generate electric sparks when the floating roof tanks stroked by lightning. This paper proposes to eliminate the conductive film on the second seal floating roof top edge and instead use a scalable grounding device (SGD) as the lightning protection measure. An empirical formula has been used to calculate the transient voltage drop when the 100,000m3 tank is stroked by lightning. The results show that the floating tank is safe when there are 20 SGDs uniformly connecting the floating roof and tank wall.

Nonlinear Vibrations and Chaos in Floating Roofs

Variational principle is used to derive the nonlinear response of the floating roof of cylindrical liquid storage tanks due to harmonic base excitations. The formulation accounts for nonlinearity due to large deflections of the floating roof. The derived nonlinear governing equation for the sloshing response of the floating roof has a cubic nonlinear stiffness term similar to the well known Duffing equation. It is shown that accounting for large deflections could substantially reduce the wave elevation for near resonance harmonic excitations. Evaluating the response of the nonlinear model for increasing amplitudes of near resonance harmonic excitations gives rise to the appearance of sub and super harmonics in the response. The broadband structure of the frequency spectrum, the fractal structure of the Poincare maps, and the bifurcation diagram as qualitative criteria and Lyapunov exponent evolution as quantitative criterion are used to investigate the emergence of chaotic response.

ELLIPTICAL DEFORMATION OF FLOATING ROOF PONTOON BY SECOND MODE RESONANCE

This paper investigates the behavior of the second mode resonance in the liquid storage tanks with the single-deck type floating roof. In the Tokachi-Oki Earthquake in 2003, the floating roof of the large-sized oil tanks received damage by sloshing. One of the reasons is considered to be elliptical deformation of the pontoon by the second mode resonance in the past report. In this paper, the behavior of the floating roof is simulated by the numerical analysis method which we propose, and the deformation and stress in the pontoon are investigated in detail. The stress of the pontoon calculated by the design method notified by the Fire Defense Agency is compared with the numerical results. By these results, the validity and the applicability of the design method are discussed.

Installation of Aluminum Domes to External Floating Roof Tanks

Installation of Aluminum Domes to External Floating Roof Tanks

Simplified Development Method of Finite Element Analysis Code for Sloshing of Floating Roof Tanks

Simplified Development Method of Finite Element Analysis Code for Sloshing of Floating Roof Tanks

Influence of roof on dynamic characteristics of dome roof tanks partially filled with liquid

The influence of roof on the natural frequencies and the modes of fixed roof, ground supported, liquid storage tanks is presented in this paper. Attention is given to partially filled tanks with the same heights of 12.19 m and the aspect ratios ( H/ R) of 2, 1.52, and 1.33. The bottom of tanks is considered to be anchored to the foundation. The effect of the roof, along with the liquid height, on dynamic properties is investigated. For this purpose, each tank is modeled in 4 liquid levels, equal to 1.80, 4.80, 8.50, and 10.90 m and in two various roof conditions: with roof (WR) and open top (OT). The finite element package ANSYS is used to model the tank–liquid systems. Tank roof and wall are meshed by shell elements and the liquid is modeled using fluid finite elements. The fluid–structure interaction is taken into account by coupling the nodes at the interface of the fluid and the shell in the radial direction. Results of ambient vibration tests are used to verify the numerical procedure in which good agreement is observed between the numerical and the experimental modal parameters. It is found that the influence of roof on natural frequencies of axial and vertical modes is negligible whereas its effect on the natural frequencies of circumferential modes is significant. It is also concluded that at low liquid levels, equal to 1.80 and 4.80 m, the tank roof does affect the axial modes of the tallest and medium height tanks while, at all of the considered liquid heights and aspect ratios, the tank roof affects the circumferential mode shapes; this confirms the idea that the roof does restrain the tank top against radial deformations.

Dynamic Response Analysis of Vertical Cylindrical Storage Tanks Based on ADINA

Storage tanks after earthquake disaster may create the serious consequence, so their anti-seismic problems have drawn greater attention, and their seismic response become the focus of research. Considering the liquid-solid coupling and the interaction between foundation and storage tanks，three different volumes of storage tanks that have different liquid height were simulated under the earthquake using the software ADINA. The liquid sloshing wave height, peak acceleration of tank wall and hydrodynamic pressure were analyzed. The results show that the peak sloshing wave height shows a rising trend basically with the increase of liquid height, and the roofs of large tanks are more easier to be destroyed by liquid sloshing. With the increase of liquid height and tank volume, the response of peak acceleration is greater. The hydrodynamic pressure increases with the decrease of liquid height. Near the bottom of tank wall the value of hydrodynamic pressure is relatively large, so elephant foot buckling is easier to happen in that area.

Study of Fire Fighting System to Extinguish Full Surface Fire of Large Scale Floating Roof Tanks

The basic characteristics of full surface fires of large scale floating roof tanks are briefed. It is pointed out that the present fire fighting systems of large scale crude oil storage depots cannot meet the need to extinguish full surface fires of large scale floating roof tanks. Adequate data of successful extinguishment of large scale tanks full surface fires and full scale tank fire experiments in the world are badly needed to design fire fighting system to extinguish full surface fires of large scale tanks in large scale crude oil storage depots. According to “Code of design for low expansion foam extinguishing system” and relative study results abroad, the fire fighting systems are calculated and designed to deal with full surface fires of large scale floating roof tanks. It is shown that designing parameters provided by API are more credible and large foam monitors act as the main fire extinguish facilities. The fire water supplying system is designed according to “Fire prevention code of petrochemical enterprise design”. The results show that the capability of the present fire fighting system should be raised up to at least 6-10 times to meet the need to extinguish full surface fires of large scale floating roof tanks. The reconstructing programs of fire fighting system are provided to deal with full surface fires of large scale floating roof tanks in the end.

A study for the setting method of floating roof tank sloshing damping device

A study for the setting method of floating roof tank sloshing damping device

Impact of concrete and PVC pipes on urban water chemistry

Waterways contain a chemical signature of catchment land use, climate and geology. This is increasingly being influenced by the urban landscape and particularly the composition of materials and activities that occur on impervious surfaces. This paper examines the degree and extent of two types of drainage materials, concrete and PVC, on urban water chemistry. This study found that water collected from a zinc and slate/tile roof and stored in a plastic rain tank (roof water) was acidic (pH 4.79) and had low bicarbonate concentrations (0.5 mg/l), water from an undeveloped catchment (reference creek) was mildly acidic (pH 5.5) with bicarbonate concentrations of 1.7 mg/l while water from a stream draining a residential catchment (urban creek) was mildly alkaline (pH 7.35) with bicarbonate concentrations of 36.3mg/l. The three types of water were then circulated through a concrete pipe or PVC pipe for 100 min and measured for a range of water chemical attributes. Roof water and water from the reference creek reported a significant increase across a range of analytes, most notably bicarbonate and calcium levels when passed through the concrete pipe, while water from the urban creek changed a lesser amount. When passed through the PVC pipe the changes in water chemistry were significantly less for roof water and urban creek water. The data suggests that in-transport processes from concrete drainage systems are having a significant influence on water chemistry, particularly where inflow is acidic. The major factor identified in this study could be attributed to the dissolution of calcium, bicarbonate and potassium ions from the concrete pipe. This could impact on receiving environments that are naturally acidic and low in bicarbonate, such as those in northern Sydney. The implications of this study point towards a need to consider the type of materials used in urban drainage networks if water chemistry and stream ecosystem health is to be protected.

Challenges in the computation of lower-bound buckling loads for tanks under wind pressures

This paper reports on the implementation of a lower-bound approach for the buckling of imperfection-sensitive shells using general purpose finite element codes. The stability of cylindrical steel tanks under wind pressure is evaluated for two tank configurations: conical roof tanks and open top tanks. For both tank configurations, several geometric relations are considered in order to find the variation of the knock-down factor as the geometry changes. The reduced energy method is implemented to compute a lower-bound for critical wind pressures and the results are compared with the static non-linear analysis carried out on the same models. An alternative way to implement the reduced energy method is presented to improve the results obtained with the proposed methodology.

FSI methods for seismic analysis of sloshing tank problems

The long-period components in earthquake ground motions, which attenuate gradually with distance, can induce sloshing waves in the liquid containment tanks although they are located far away from the seismic source. The resulting sloshing waves generate additional forces impacting the wall and roof of the tanks and may cause extensive damage on the tank structure. Numerous examples of tank damages due to sloshing of fluid have been observed during many earthquakes. Nevertheless, the effect of sloshing is usually primitively considered in most of the seismic design codes of tanks. On the other hand, the derivation of an analytical solution for the sloshing response of a liquid storage tank subjected to harmonic excitation includes many assumptions and simplifications. Most of the analytical solutions in the recent literature assumed the containing liquid to be invicid, incompressible and irrotational, and the tank structure to be an isotropic elastic plate with uniform stiffness, mass and thickness. Even though, experimental works are necessary to study the actual behavior of the system, they are time consuming, very costly and performed only for specific boundary and excitation conditions. However, appropriate numerical simulation using fluid structure interaction techniques can be used to predict the hydrodynamic forces due to the high-speed impacts of sloshing liquid on a tank wall and roof. These simulations can reduce the number of experimental tests. The nonlinear finite element techniques with either Lagrangian and/or Eulerian formulations may be employed as a numerical method to model sloshing problems. But, most of the Lagrangian formulations used to solve such problems have failed due to high mesh distortion of the fluid. The arbitrary Lagrangian Eulerian techniques are capable of keeping mesh integrity during the motion of the tank. In this study, an explicit nonlinear finite element analysis method with ALE algorithm is developed and sloshing phenomenon is analyzed. The analysis capabilities of the method are explained on a technical level. Although, the developed numerical procedure is applicable to deformable structures, the accuracy of the method is validated with the existing analytical formulation derived from potential flow theory as well as the experimental data carried out on rigid tanks when subjected to harmonic and earthquake ground motions. High consistency between numerical and experimental results in terms of peak level timing, shape and amplitude of sloshing waves is obtained not only for non-resonant excitation but also for resonant frequency motion.

Seismic Analysis of Hydrodynamic Sloshing Force on Storage Tank Roofs

Large-amplitude sloshing caused by earthquakes may result in liquid impact on the roof of liquid storage tanks. The motivation for this study is better understanding of the sloshing-induced impact via experimental investigations and establishing an analytical approach for evaluation of the maximum impact force on tank roofs. The experimental tests are carried out using a rectangular liquid tank excited by harmonic oscillations. The effects of geometric parameters such as the tank aspect ratio, excitation amplitude and freeboard on maximum liquid impact force are investigated by conducting 140 tests. Based on the conservation of fluid momentum, an analytical solution is developed to model sloshing impact force on tank roofs. The analytical solution parameters are calibrated using the experimental measurements. Finally, the analytical scheme is extended for a systematic process to evaluate the hydrodynamic and hydrostatic components of impact forces for earthquake engineering application.

Axisymmetric Finite Element Analysis for Sloshing Response of Floating Roofs in Cylindrical Storage Tanks

Floating roofs are widely used to prevent evaporation of the contents of large oil storage tanks. The 2003 Tokachi-Oki earthquake caused severe damage to floating roofs due to liquid sloshing. Establishing the structural integrity of floating roofs subjected to sloshing is an urgent issue for the petrochemical and oil refining industries. The present paper proposes an axisymmetric finite element analysis for the sloshing response of floating roofs in cylindrical storage tanks. The hydrodynamic coupling of the fluid and the floating roof under seismic excitation is taken into consideration in the analysis. The fluid is assumed to be incompressible and inviscid, and the roof is assumed to be linear elastic. In addition, the sidewall and the bottom are assumed to be rigid. The theory for the finite element analysis, in which the behavior of the fluid is formulated in terms of dynamic pressure using the Eulerian approach, is proposed. The basic vibration characteristics of the floating roof, such as the natural frequencies and vibration modes, can be obtained from this analysis. These characteristics provide engineers with important information on the floating roof design.