Horizontal tank strength analysis considering nozzle loads and horizontal deviations

When assessing the reliable and safe operation of technological equipment, and in particular, capacitive-type equipment, a fairly diverse number of methods are used. However, all current procedures do not sufficiently take into account the impact of certain factors on the forming stressed-deformed state of the object. Usually, when assessing the actual technical condition of an object, the level of defect of the object is determined, and appropriate calculations are carried out according to the criterion of the dominant damage mechanism. A significant impact on the stressed-deformed state of the shell structure can be exerted by the level of loads on process nozzles from the connection of process pipelines, as well as possible deviations during installation work. One of these deviations may be a deviation from the horizontal of the housing when installing supports on the foundation. Moreover, the combination of the action of the above factors can have a determining negative effect on the strength, and, accordingly, the operational reliability of the technical device. In the modern world, technological progress does not stand still and the consequence of this is the development of a fairly extensive number of software products that allow you to simulate possible individual scenarios for the development of unfavorable processes and predict the behavior of the object under the conditions under consideration. In this work, studies are carried out on the strength analysis of the horizontal tank, taking into account various values of loads on the nozzle of the body diameter, as well as taking into account the deviation of the tank body from horizontal.


Introduction
When examining the current technical condition of shell structures operated at oil and gas facilities, all work is carried out in strict accordance with the requirements of regulatory and technical documentation.And these works do not provide for modeling using software complexes.However, successful attempts are being made to introduce numerical methods into the work to solve the above problems and conduct a more reliable assessment of the technical condition [1][2][3][4][5][6][7][8][9][10].Numerical methods allow you to more accurately determine the most weak points of the structure and develop recommendations for preventing accidents for technical reasons.In the process of assessing the possibility of further safe operation of the facility, the main focus is on technical parameters (pressure, temperature, etc.), prevailing degradation processes, as well as the degree of defect of the facility.Strength tests are carried out.As a rule, strength calculations are carried out without taking into account loads on process nozzles, and nozzles of small diameter 50mm and less are often discarded from the field of view due to their low significance.Mounting deviations are also possible, expressed in deviation from horizontal, vertical, etc.The combination of mutual influence of several factors can have a determining value on the further condition of the equipment.Numerical modeling using software complexes allows you to come close to solving this issue.Therefore, the actual work is to analyze the distribution of stresses in the tank housing when taking into account the loads on the process nozzles and the deviation of the housing from horizontal.

Research methodology
The object under consideration is a horizontal vessel operating at a pressure of 0.6 MPa and a temperature of 30 С.Structural elements of the vessel are: a cylindrical shell of the housing, elliptical bottoms, a settler in the cylindrical part of the housing, process unions of various diameters, as well as two saddle supports, one of which is fixed and the other is movable.
For strength analysis, the licensed software package «KOMPAS-3D» was used with the integrated APM FEM system for solving engineering and research problems.At the first stage, a capacity model was developed in the COMPASS-3D program.The 3D model of the capacity is shown in Figure 1.Next, loads were applied in the APM FEM strength analysis system, such as: pressure and temperature; force and moments acting on process connector A with size of 576 mm; necessary fasteners are installed.Table 1 shows the values of allowable load on nozzle A according to the operational and technical documentation.The capacity strength analysis consisted of the following steps: 1) tank SDS study without taking into account the deviation of the tank body from the horizontal with the application of loads on nozzle A equal to 25, 50 and 75% of the permissible; 2) the tank SDS study without taking into account the application of loads on nozzle A, taking into account the deviation of the tank body from horizontal by moving the movable left support down relative to the right fixed support by 10 mm and 15 mm; 3) tank SDS study with simultaneous taking into account the application of loads on nozzle A equal to 25, 50 and 75 % of the permissible loads and taking into account the deviation of the tank body from horizontal by shifting the movable left support down relative to the right fixed support at values of 10 mm and 15 mm.

Research results and discussion
Initially, a strength analysis was carried out for the tank body, taking into account the different values of loads on nozzle A from permissible loads and without taking into account the deviation from horizontal.The results are shown in Figure 2 (a-c).It can be seen from Figure 2 that the distribution of stresses in the vessel housing is ambiguous, the maximum stresses are concentrated in the right elliptical bottom, and when the loads on the nozzle increase, the maximum stresses increase.
Further, a strength analysis of the vessel casing was performed without taking into account the loads on the nozzle A, but taking into account the deviation from the horizontal of the vessel casing according to stage 2).
Results are shown in Figure 3.As can be seen from Figure 3, an increase in the displacement of the support relative to the other downward by values of 10 and 15 mm leads to a change in the dislocation of the place of concentration of maximum stresses and an increase in the values of maximum stresses.However, if you compare the results shown in Figure 2 with the results of Figure 3, you can find that the most significant contribution to the increase in maximum stresses is still an increase in the load on nozzle A, and not a deviation from horizontal.
Further, calculations were carried out with simultaneous consideration of loads on nozzle A equal to 25, 50 and 75% of permissible loads, and without taking into account deviation from horizontal.Calculation results are given in Table 2. Analyzing Table 2, we can conclude that the combined action of loads on the nozzles and the deviation from the horizontal of the tank body with different values leads to a sharp increase in the values of maximum stresses.
In order to reduce the values of maximum stresses and thereby increase the strength of the container body, it is proposed to install two stiffening rings on the container body from the outside along the entire circumference of the outer diameter.The rings are sheet steel with a width of 300 mm and a thickness of 100 mm.The rings are located at a distance of 815 mm and 2920 mm from the place of coupling of the left elliptical bottom with the shell of the housing.The worst case was considered when the values of loads on nozzle A are 75 % of the allowable value and the value of deviation from the horizontal of the tank body is 15 mm.The results of strength analysis with stiffening rings are shown in Figure 4. From the results shown in Figure 4, it can be seen that the stresses when using two stiffening rings in certain places decreased from a value of 304.8 MPa to a value of 231.9 MPa by 1.3 times.

Conclusions
Based on the results of the tank simulation, taking into account the loads on the union with a nominal diameter of 50 mmd from the horizontal of the tank body, the following conclusions can be drawn: • it was found that the most significant contribution to the growth of maximum stresses is the increase in the load on the nozzle, and not the deviation from horizontal.• it is shown that the values of maximum stresses taking into account the load on the nozzle and deviations from horizontal can be significantly reduced by using stiffening rings of a certain

Figure 2 .
Results of strength analysis for the vessel housing by the strength of loads on the nozzle A equal to 25, 50 and 75% of the permissible loads, and without taking into account the deviation from horizontal: a) -results of strength analysis for the vessel housing taking into account loads on nozzle A 25% of allowable loads; b) -results of strength analysis for the vessel housing taking into account loads on the nozzle A50% of permissible loads; c) -results of strength analysis for the vessel housing taking into account the loads on the nozzle A 75% of the permissible loads.

Figure 3 .
Figure 3. Results of strength analysis for vessel casing without consideration of loads on nozzle A and with consideration of deviations from horizontal: a) -results of strength analysis for the vessel body taking into account the deviation of the vessel body from the horizontal by shifting the movable left support down relative to the right fixed one by a value of 10 mm; b) -results of strength analysis for the vessel housing taking into account the deviation of the vessel housing from horizontal by shifting the movable left support down relative to the right fixed support by the value of 15mm.

Figure 4 .
Figure 4. Strength analysis results with stiffening rings.

Table 1 .
Values of allowable loads on connector A according to operational and technical documentation.

Table 2 .
Results of strength analysis for the vessel housing by the strength of loads on the nozzle A equal to 25, 50 and 75% of the permissible loads, and taking into account the deviation from horizontal by 10 and 15 mm.