Portable tank and tank container for liquefied gas transportation

Abstract

A tank container for transporting and storing liquefied gas, including a tank that includes a cylinder body and two heads arranged oppositely and welded with both ends of the cylinder body; and a frame assembly for fixing and supporting said tank, which includes a front frame and a rear frame fixed at both ends of said tank respectively. The cylinder body has a shell thickness δ substantially equal to: Pc×Di/(2σb/Ks−Pc), wherein, Pc is the calculated pressure of the tank, required by the transported liquefied gas, Di is the inner diameter of the cylinder body, σb is the maximum tensile strength of material of the cylinder body at a normal temperature, and Ks is a safety factor no larger than 2.6. The tank container is designed through stress analysis methods, the safeness of which has been verified.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more evident from the detailed description of the preferred but not exclusive embodiment illustrated indicatively in the accompanying drawings wherein:

FIG. 1 is a front elevational view of a tank container for liquefied gas transportation and storage according to the prior art;

FIG. 2 is a front elevational view of a ultra-light tank container for liquefied gas transportation and storage according to the present invention, showing neck rings welded between the heads of the tank and the corresponding frames to connect the tank and the frames, and having a diameter less than that of the cylinder body of the tank;

FIG. 3 is a side elevational view of the container in FIG. 2;

FIG. 4 is a top elevational view of the container in FIG. 2, showing short longitudinal beams arranged on both frames for connecting locally with the tank;

FIG. 5 is a separate unit view for stress analysis of the tank container according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 2, according to the present invention, a tank container 80 for transporting liquefied gas includes a tank 81 and a frame assembly 82 for fixing and supporting the tank 81. The tank 81 includes a cylinder body 811 and two heads 812 welded respectively on opposite ends of said cylinder body 811. The frame assembly 82 includes two individual frames, that is, a front frame 821 and a rear frame 822 disposed close to two ends of the tank 81 respectively. The tank 81 and the frame assembly 82 are connected together through neck rings 85 being welded between the heads 812 and corresponding front and rear frames 821 and 822. Said neck ring 85 has a diameter less than that of the cylinder body 811. A safety attachment 83 is arranged on the tank 81 to secure the cargos in the tank. An adumbral plate 84 is preferably mounted on the tank 81 to reduce the rising of the temperature in the tank. Preferably, short longitudinal beams 86 are arranged on both the front frame 821 and the rear frame 822, in order to connect the front and rear frames locally with the tank 81 respectively.

According to the present invention, the front frame 821 is equipped with two top corner members 824 for fastening and hoisting at its two top corners and with two bottom corner members 825 for stacking and hoisting at its two bottom corners. Similarly, the rear frame 822 is also equipped with two top corner members 824 for fastening and hoisting at its two top corners and with two bottom corner members 825 for stacking and hoisting at its two bottom corners, which can be seen clearly in FIG. 3.

As shown in FIGS. 2, 3 and 4, the deadweight of the container 80 according to the present invention is mainly determined by the weight of the tank 81, the frame assembly 82, the neck rings 85, and the short longitudinal beams 86 for local supporting. Since the tank 81 should be loaded with pressurized liquefied gas, steel plates thicker than the structure of the frame 82 are used to manufacture the cylinder body 811 and the heads 812 of the tank. Thus, the weight of the tank 81 takes the main part of the deadweight of the whole container. Moreover, the outer diameter of the cylinder body 811 should be within the maximum width of the frame assembly 82, and the inner diameter Di of the cylinder body 811 determines the volume for loading cargos, therefore the shell thickness δ of the cylinder body 811 becomes the most important parameter that affect the deadweight of the tank.

It is noteworthy that above-mentioned and other standards for calculating the shell thickness is not permanent and are subject to change from time to time. According to the present invention, the shell thickness δ of the cylinder body 811 of the portable container 80 is designed and calculated on the basis of the calculation method for fixed container with a safety factor K_s not larger than 2.6, i.e.,

δ=P_c×D_i/(2σ_b/K_s−P_c)  (*)

where

• • P_c is the calculated pressure;
  • D_i is the inner diameter of the cylinder body;
  • σ_b is the maximum tensile strength of material of the cylinder body at a normal temperature; and
  • K_s is the safety factor that is no larger than 2.6.

In the U.S. Pat. No. 6,012,598, the shell thickness T_s of the cylinder body is substantially equal to P R_i/(⅓S_u−0.5P), which is equivalent to the calculation of the present invention P_c×D_i/(2_b/K_s−P_c) with the safety factor K_s of 3. In an embodiment of the invention, the material of the cylinder body has a maximum tensile strength of 80,000 psi (552 MPa) while the tank is designed to transport liquefied gas under 27.5BAR and have a volume of 22.5 cubic meters. The shell thickness of the cylinder body calculated through the equation (*) of the present invention with a safety factor K_s of 2.6 is less than that calculated through the equation disclosed in the U.S. Pat. No. 6,012,598 by 2.43 mm, with the deadweight of the tank reduced by 625 kg. With a safety factor K_s of 2.5, the shell thickness according to the invention is less than that according to the U.S. Pat. No. 6,012,598 by 3.08 mm, with the deadweight of the tank reduced by 792 kg. And with a safety factor K_s of 2.4, the shell thickness according to the invention is less than that according to the U.S. Pat. No. 6,012,598 by 3.64 mm, with the deadweight of the tank reduced by 936 kg.

According to the U.S. Pat. No. 6,012,598, the material for the cylinder body is required to have a maximum tensile strength larger than 80,000 psi (552 MPa); while in the present invention, the material, for the cylinder body is required to have a maximum tensile strength no less than 470 MPa. Thus the material range for selection becomes larger.

As disclosed in the U.S. Pat. No. 6,012,598, the shell of the head should be thicker than that of the cylinder body. On the contrary, according to the present invention, the head 812 is designed by using an ellipticity of 1:1.9 and stress analysis method, so that the calculated thickness of the head 812 is less than or equal to the shell thickness of the cylinder body 811. Therefore, the deadweight of the tank 81 is further reduced through reducing the thickness of the head 812. For example, in the above-mentioned embodiment of the invention, the thickness of the head according to the invention can be less than that according to the U.S. Pat. No. 6,012,598 by 2.84 mm, so that the deadweight of the tank can be further reduced.

As disclosed in the U.S. Pat. No. 6,012,598, the connection of the tank and the frame is realized by welding with neck rings of the same diameter as that of the cylinder body. According to the embodiment of the present invention shown in FIG. 2, the connection of the tank 81 and the frames 821, 822 is realized through welding the neck rings 85 between the heads 812 of the tank and corresponding front and rear frames 821 and 822. Since the neck ring 85 has a diameter less than that of the cylinder body 811 of the tank 811, the deadweight of the container 80 can be reduced by reducing the weight of the neck ring 85.

As disclosed in the U.S. Pat. No. 6,012,598, two upper and two lower rails connect directly the two ends of the frame in order to transfer loads. As shown in FIG. 4, according to the invention, the tank 81 is designed as a load transferring member. In particular, the load between the front and rear frames 821 and 822 is transferred through two neck rings 86 and the tank 81. Two short longitudinal beams 86 are extended from the bottom portion of each of the frames 821, 822 and connected to the predetermined portions on the bottom of said tank 81 respectively for supporting and strengthening. Of course, only one or more than two short longitudinal beams 86 can be arranged on either front or rear frames. Thus, the supporting structure of the frame assembly 82 is simplified and the deadweight of the tank container is therefore reduced.

To verify the technical safeness of the tank container 80, Finite Element Analysis (FEA) is used. As shown in FIG. 5, the tank container 80 is separate into a plurality of units for stress analysis. The ANSYS software for FEA is used to simulate the stress situations under various loadings (including dynamic loadings) during the transportation. The structure of the container 80 is being adjusted, until the stress at every position of the container is within the allowable stress of the material used. It should note that the maximum stress point may change under different loadings, for example, among the ranges A₁ to A₅, wherein A₁ indicates the center area of the cylinder body, A₂ indicates the upper transverse beam area of the frame, A₃ indicates the center area of the end sealing member, A₄ indicates the short longitudinal beam area, and A₅ indicates the top corner member area.

For example, in the case that the maximum tensile strength of the material of cylinder body is 80,000 psi while the tank is designed to transport 27.5BAR liquefied gas and have a volume of 22.5 cubic meters, the maximum stress point of the tank container will be in the top corner member area A₅ under the stacked loadings, in the center area A₁ of the cylinder body under the hoisting loadings, in the short longitudinal beam area A₄ under the outer longitudinal fastening loadings, or in the center area A₁ of the cylinder body under the pressure testing loadings.

The technical safeness of the present invention has been verified through the experimental test approved by the competent authority in China.

It is understandable that the portable tank 81 of the present invention should not be limited to the application of tank container, which can be also fixed on a chassis of a vehicle through a frame structure similar to the frame assembly 82 or the like to form a tank vehicle.

Although several preferred embodiments of the present invention have been described, the present invention may be used with other configurations. It will be appreciated by those skilled in the art that, the present invention could have many other embodiments, and changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims and equivalents thereof.

Claims

1. A portable tank for transporting and storing liquefied gas, including a cylinder body and two heads arranged oppositely and connected with both ends of the cylinder body respectively, wherein the cylinder body has a shell thickness a calculated through stress analysis design methods for fixed containers, and substantially equal to: Pc×Di/(2σb/Ks−Pc)where Pc is the calculated pressure of the tank, required by the transported liquefied gas,Di is the inner diameter of the cylinder body,σb is the maximum tensile strength of material of the cylinder body at a normal temperature, andKs is a safety factor that is not larger than 2.6.

2. The tank according to claim 1, wherein the safety factor Ks is taken as 2.5.

3. The tank according to claim 1, wherein the safety factor Ks is taken as 2.4.

4. The tank according to claim 1, wherein the safety factor Ks is taken as 2.6.

5. The tank according to claim 1, wherein the shell thickness of the head is less than or equal to that of the cylinder body.

6. The tank according to claim 1, wherein the maximum tensile strength σb of the material of the tank is no less than 470 MPa.

7. A tank container for transporting and storing liquefied gas, including: a tank, including a cylinder body and two heads arranged oppositely and connected with both ends of the cylinder body respectively; anda frame assembly for fixing and supporting said tank, including a front frame and a rear frame fixed at both ends of said tank respectively,wherein, the cylinder body has a shell thickness δ substantially equal to Pc×Di/(2σb/Ks−Pc)where Pc is the calculated pressure of the tank, required by the transported liquefied gas,Di is the inner diameter of the cylinder body,σb is the maximum tensile strength of material of the cylinder body at a normal temperature, andKs is a safety factor that is not larger than 2.6.

8. The tank container according to claim 7, wherein the safety factor Ks is taken as 2.5.

9. The tank container according to claim 7, wherein the safety factor Ks is taken as 2.4.

10. The tank container according to claim 7, wherein the safety factor Ks is taken as 2.6.

11. The tank container according to claim 7, wherein the shell thickness of the head is larger than or equal to that of the cylinder body.

12. The tank container according to claim 7, wherein the maximum tensile strength σb of the material of said tank is no less than 470 MPa.

13. The tank container according to claim 7, wherein each of said front and rear frames is welded with one corresponding head of said tank through a neck ring having a diameter less than that of the cylinder body, so that the load between said front and rear frames is transferred through said tank and said neck rings.

14. The tank container according to claim 13, further including a plurality of short longitudinal beams that are extended from the bottoms of said front and rear frames and connected to the predetermined portions on the bottom of said tank, respectively.