FREIGHT CONTAINER

Abstract

A freight container for transporting a pressurized fluid at a design pressure P, including a tank and mounted within an ISO frame. The tank includes a vessel formed of a material having an ultimate tensile strength SU. The vessel has a cylindrical shell having an inside radius RI and a thickness Ts which is less than that of prior art freight containers and substantially equal to: (P*Ri)/((Su/Xa)−(Xb*P)). Such a vessel conforms to ASME Boiler and Pressure Vessel Code, Section VIII, Division 2. The freight container may be mounted on a transport vehicle, before or after being filled with the pressurized fluid, and transported to a remote location.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a freight container according to the present invention.

FIG. 2 is a top view of the freight container of FIG. 1.

FIG. 3 is an end view of the freight container of FIG. 1.

FIG. 4 is a schematic view of the freight container of FIG. 1 mounted on a transport vehicle.

DETAILED DESCRIPTION OF THE INVENTION

A freight container 10 for transporting pressurized fluids having a service (or design) pressure P_w of at least 100 psi and not over 500 psi is shown in FIGS. 1-3. As is explained in more detail below, the freight container 10 has a novel tank design which results in a decrease in the container's tare weight when compared to prior art freight containers. While the aforementioned is described having a working pressure P_w between 100 psi and 500 psi, it is contemplated that the freight container of the embodiments of the subject invention may have a working pressure in the range between 50 psi and 750 psi.

The freight container 10 may includes a tank 12 and a frame 14. The tank 12 may include a shell 24, which may be generally cylindrical, and two heads 26 affixed on distal ends of the shell 24. The dimensions of the shell 24 may be defined by an outer radius R_o and an inner radius R_i, the difference there between resulting in the shell's thickness T_s.

The heads 26 may include an elliptical end portion 30 and a straight flange 32 extending from the outer circumference of the elliptical end portion 32 to the respective axial end of the cylindrical shell 24. The affixed heads 26 may be welded to the shell 24. Both the shell 24 and the heads 26 may be constructed of a high strength steel, for example SA612N, which for the thicknesses involved has an ultimate tensile strength S_u of about 81,000 psi. However, other material may be used having a tensile strength in the more general range of 60,000 psi and 100,000 psi. More specifically materials having a tensile strength in the range between 70,000 psi and 90,000 psi may be utilized to construct the freight container 10.

The frame 14 may function to transmit static and dynamic forces arising out of the lifting, handling, securing, and transporting of the freight container as a whole. The frame 14 may include posts 52, rails 54, braces 56, skirt support members 58 and other load-bearing elements which are not present for the purposes of containing cargo. These components of the frame 14 are joined at eight corner fittings 60 to form its base structure, its end structure and its side structure. The frame 12 may fully or only partially satisfy the requirements of ISO 1496-3 Sections 5.1-5.5. Other frame structures which satisfy the requirements of ISO 1496-3 Sections 5.1-5.5 are possible with, and are contemplated by, the embodiments of the present invention.

The skirt support members 58 provide connections between the frame 14 and the tank 12. The skirt support members 58 are cylindrical extensions of the shell 24. The skirt support members are welded to the braces 62, shown in FIG. 3, which extends between the posts 52 and the rails 54 of each end of the freight container 10.

The freight container 10 may also include certain additional components, such as a sun screen 72 (FIGS. 1 and 2) if necessary in view of the pressurized fluid being temperature sensitive and/or if the transportation will occur in an environment of temperature extremes. The freight container 10 may also include internal baffles 74 to limit surging when the vehicle carrying the freight container stops or starts.

The tank 12 may be manufactured in accordance with Section VIII Division 2 of the ASME Boiler and Pressure Vessel Code covering unfired pressure vessels. The entire disclosure is this Division is hereby incorporated by reference. In one embodiment, the minimum thickness T_s of the shell 24 is substantially:

T _s=(P_w*R_i)/((S_u/X_a)−(X_b*P_w)), where

P_w=the internal design pressure for the tank;

R_i=inside radius of tank's shell;

X_a=scalar factor relating to the maximum allowable stress;

X_b=scalar factor relating to the internal design pressure; and,

S_u ultimate tensile strength; and

where X_a is generally in the range greater than 1.5. More specifically X_a may be in the range between 1.5 and 3.0. In one embodiment, X_a may be substantially 2.5. The scalar X_b may in the range from 0 to 1. In one embodiment, X_b may be substantially 0.5.

Calculations may be performed to determine the minimum thickness for the shell at three different design pressures (335, 400, and 455 psig) and an ultimate tensile strength of about 69,900 psi. The pressures selected represent three different common design pressures of freight containers for fluids under pressure, and the tensile strength represents typical container material. For comparative purposes, a value of 0.5 was assumed for the scalar factor X_b. The weight of the shell of the tank 12 is reduced by an amount greater than 25% and the weight of the heads by 6% from that of otherwise identical tanks made according to Division 1, Section VIII of the ASME Code.

One may now appreciate that the present invention provides a novel freight container with a tank design which results in a decrease in the freight container's tare weight. Although the invention has been shown with respect to certain preferred embodiment, equivalent and obvious alternations will occur to those skilled in the art upon the reading and understanding of this application. The present invention includes all such alterations and modifications and is limited only by the scope of the following claims.

The invention has been described herein with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alternations in so far as they come within the scope of the appended claims or the equivalence thereof.

Claims

1. A tank for storing a pressurized substance at a design pressure Pw, comprising: a shell having a wall thickness Ts, an inner radius Rinternal and tensile strength Su;one or more head caps affixed to the shell; and,wherein the wall thickness Ts is defined by the equation: Ts=(Pw*Ri)/((Su/Xa)−(Xb*Pw))wherein Xa is a scalar greater than 1.5.

2. The tank as defined in claim 1, wherein the scalar Xa is in the range between 1.5 and 3.

3. The tank as defined in claim 1, wherein the scalar Xa is substantially equal to 2.5.

4. The tank as defined in claim 1, wherein the design pressure Pdesign is in the range between 50 and 750 psi.

5. The tank as defined in claim 1, wherein the design pressure Pdesign is in the range between 150 and 550 psi.

6. The tank as defined in claim 1, wherein Xb is a scalar less than 1.

7. The tank as defined in claim 6, wherein Xb is substantially equal to 0.5.

8. The tank as defined in claim 1, wherein Su is in the range between 60,000 psi and 100,000 psi.

9. The tank as defined in claim 1, wherein Su is in the range between 80,000 psi and 90,000 psi.

10. The tank as defined in claim 1, further comprising: one or more valves permitting the transfer of the associated pressurized substance to and from the tank.

11. A freight container for transporting a pressurized substance at a design pressure Pw to a remote location, the freight container comprising: frame for transmitting static and dynamic forces arising from transportation of the freight container as a whole; and,a tank received within the frame, wherein the tank includes: a shell having a wall thickness Ts, an inner radius Rinternal and tensile strength Su;one or more head caps affixed to the shell; and,wherein the wall thickness Ts is defined by the equation: Ts=(Pw*Ri)/((Su/Xa)−(Xb*Pw))wherein Xa is a scalar greater than 1.5.

12. The freight container as defined in claim 11, wherein the scalar Xa is in the range between 1.5 and 3.

13. The freight container as defined in claim 11, wherein the scalar Xa is substantially equal to 2.5.

14. The freight container as defined in claim 11, wherein the design pressure Pdesign is in the range between 50 and 750.

15. The freight container as defined in claim 11, wherein the design pressure Pdesign is in the range between 150 and 550.

16. The freight container as defined in claim 11, wherein Xb is a scalar less than 1.

17. The freight container as defined in claim 16, wherein Xb is substantially equal to 0.5.

18. The freight container as defined in claim 11, wherein Su is in the range between 60,000 psi and 100,000 psi.

19. The freight container as defined in claim 11, wherein Su is in the range between 80,000 psi and 90,000 psi.

20. The freight container as defined in claim 11, further comprising: one or more valves permitting the transfer of the associated pressurized substance to and from the freight container.