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

This utility patent application claims priority to U.S. provisional patent application Ser. No. 60/829,418 filed on Oct. 13, 2006, which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to a freight container for pressurized fluid commonly known as a tank container.

BACKGROUND OF THE INVENTION

Conventionally, a freight container is considered an article of transport equipment having an internal volume of 1 m³ (35.3 ft³) or more. A freight container is intended for repeated use, and it is specifically designed to facilitate the carriage of goods by one or more modes of transportation, without intermediate reloading. A freight container may be fitted with devices permitting its ready handling, such as its transfer from one mode of transport to another.

An ISO container is a freight container complying with relevant ISO container standards in existence at the time of its manufacture. The ISO is an international standards setting organization, and compliance with its standards may not be mandatory. International Standards ISO 668 (5th edition) and ISO 1496-3 (4th edition) are hereby incorporated by reference.

The present application particularly concerns freight containers used to transport pressurized materials such as, for example, pressure liquefied gases including chlorine, anhydrous ammonia, and fluorocarbons. Fluids such as these are shipped in tank containers with a maximum allowable working pressure between 100 and 500 psi. The upper limit, 500 psi, is not a theoretical limit, but a regulatory one, and the applicant expects that if and when the pertinent regulations allow higher pressures, freight containers will be built to sustain such higher working pressures.

Freight containers, including the freight container of the embodiments of the present invention, for the transport of pressurized materials such as pressure liquefied gasses may be mounted on a transport vehicle (such as a truck, ship, or railroad car), before or after being filled with a pressurized material, and then transported to a remote location. In most countries, freight containers must be approved for use by a competent authority (or its designated body) appointed by the specific country's government. For example, in the United States, these freight containers must be approved by the Department of Transportation (D.O.T.). Further in most countries the competent authority adopts in whole or in part, a recognized pressure vessel code. For example, the U.S. D.O.T. has adopted the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, with some additional limitations.

In the past, the tanks of such freight containers for fluid under pressure have been designed and constructed in accordance with a recognized pressure vessel code, which in the United States is Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code covering unfired pressure vessels. The entire disclosure of this Division is hereby incorporated by reference. When these tanks are used at normal environmental conditions of temperature and pressure to hold and transport fluids, the minimum thickness T_s, of the shell has been determined by the following equation:

T_s=(P_design*R_i)/((E*S_DIV.1)−(0.6*P_design)), where

P_design=the internal design pressure for the tank;

R_i=inside radius of tank's shell;

S_DIV.1=tensile strength factor relating to the maximum allowable stress; and,

E=joint efficiency.

The joint efficiency, E, has a value of between 0 and 1, depending on the extent of radiography of the welded joints. When all welded joints are fully X-rayed, E has a value of 1 and essentially drops out of the equation. (In Division 2, all welded joints are required to be fully X-rayed, so this factor does not appear in the equation.)

These prior art freight containers have satisfied the competent authorities in various countries concerned with approval of freight containers, including the United States Department of Transportation which is commonly viewed in the industry as having the most stringent approval requirements. Again it is noteworthy that the ASME Boiler and Pressure Vessel Code is not a permanent, standard and is subject to change from time to time.

Tank containers made according to Division 1 of the ASME Boiler and Pressure Vessel Code, Section VIII, which have a capacity of about 4500 U.S.W.G. (U.S. water gallons) and a design pressure of between 335 and 400 psi, have had a tare weight of between about 17,000 lbs and 20,000 lbs. This means that when filled to capacity and placed on a truck for transport over a highway, the tank container can easily cause the truck to exceed the weight limits established for such roads. Perhaps the most restrictive country in this regard is Japan, where a tank container should not exceed 53,000 lbs. when loaded. As a result of such load limits, many tank containers can be filled only partially, depending on the density of the fluid being shipped, and this can make them inefficient.

BRIEF SUMMARY

A freight container for transporting a pressurized fluid, also termed a tank container, includes a tank (or shell) and a framework (or frame) surrounding the tank. The tank may incorporate various pipes and fittings which are designed to contain the cargo carried and to permit the tank to be filled and emptied. The tank may be formed from a cylindrical shell and two heads, one closing each end of the cylindrical shell. The dimensions of the shell include an outer radius R_o and an inner radius R_i, the difference there between defining the shell's thickness T_s.

The shell and heads of a tank container may be constructed of a material meeting the requirements of the approved pressure vessel code or approved by the competent authority. Typically in the United States the shell and heads of tank containers have been made from a high strength steel, for example SA612N, having an ultimate tensile strength (S_u) of 81,000 psi.

The framework of an ISO freight container for pressurized fluids includes tank mountings, end structures and other load-bearing elements which may not be present for the purposes of containing the fluid. The framework functions to transmit static and dynamic forces arising out of the lifting, handling, securing, and transporting of the freight container as a whole. The framework may include eight corner fittings (four top corner fittings and four bottom corner fittings), rails, posts, and braces which form its base structure, its end structure and its side structure and may satisfy the requirements of ISO 1496-3 Sections 5.1-5.5. In the context of the present application, the term “ISO frame” means a framework which satisfies the framework requirements of these sections.

An ISO freight container for pressurized fluid may also include certain additional components depending on the intended use of the container. For example, if the pressurized fluid is temperature sensitive and/or if the transportation will occur in a temperature extreme environment (i.e., hot or cold ambient temperatures), the freight container may include sunscreens, linings, jacketing (cladding), insulations, air baffles, etc.

The embodiments of the present invention provide a novel ISO freight container having a tank design which results in a decrease in the freight container's tare weight. In a preferred embodiment, the present invention provides a freight container for transporting a fluid at a pressure P, typically between 100 psi and 500 psi. The freight container may include a tank and an ISO frame. The tank may be made with a shell and heads that have an ultimate tensile strength (S_u) of substantially 81,000 psi. The shell of the cylindrical vessel may have a thickness T_s, given by:

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 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 factor X_b may be in the range between 0 and 1. More specifically, X_b may be 0.5. However, it is contemplated in another embodiment that X_b may be between 1 and 5. It is noted here that the shell may be manufactured to the above thickness with a typical manufacturing tolerance of (plus or minus) +/−6%.

Freight containers according to the embodiments of the present invention have satisfied the requirements of The United States Department of Transportation. Thus, a freight container according to the embodiments of the present invention may be mounted on a transport vehicle (such as a truck or railroad car), before or after being filled with a pressurized fluid, and then transported to a remote location. Freight containers according to the embodiments of the present invention have a tare weight approximately 2000 lbs less than comparable prior art freight containers where both have a capacity of about 4500 U.S.W.G. and a design pressure of 335 to 365 psi.

The embodiments of the present invention provides these and other features hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail an illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.

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.