Abstract:
An improved mobile fluid storage tank having a base, substantially vertical front wall, a substantially rear wall, a pair of substantially parallel side walls and a roof structure. The roof structure has a rear roof portion and a front roof portion. The rear roof portion is substantially parallel with the base and extends along the rear portion of the two side walls while the front roof portion is comprised of a single sloping section which extends from the forward end rear roof portion to the vertical front wall. The intersection of the front and rear roof portions being selected to provide the optimum volume of fluid content of the tank.

Description:
TECHNICAL FIELD 
     The present invention relates to a mobile liquid storage tank trailer. More particularly, the present invention relates to an improved mobile storage trailer with enhanced characteristics permitting it to accommodate an increased volume of fluid. 
     BACKGROUND OF THE INVENTION 
     There are a number of different types of liquid storage tank trailers which can be towed from one location to another. Examples of such include are shown in U.S. Pat. Nos. 6,152,492; 5,004,269; and 4,874,184. These fluid storage tank trailers are generally trapezoidal-shaped or stepped from the forward end to the rearward end to enable it to be supported at the rear end by an axle and wheels/tires when the fluid tank has its front end lifted and is secured behind a towing tractor vehicle. 
     The shape of the storage tank is influenced by maximum, non-permitted road height limitations when the tongue of the trailer is attached to the fifth wheel of a towing tractor. In the United States the front end of such a trailer once attached to a tractor is usually limited to between about 13.5 feet and 14 feet, without permitting. Therefore, the front end is necessarily designed about 48 to 50 inches shorter so that once installed on the fifth wheel of a tractor, it falls below the maximum non-permitted road height limitation. 
     The problem with existing trailer designs is the general limitation associated with the amount of volume that any given trailer can accommodate in view of non-permitted road height and width limitations. These trailers are typically used to store hydraulic fracturing fluid which is used in the fracturing of an oil or gas formation. As such, the existing designs typically accommodate maximum volumes of approximately 500 barrels. Such trailers are transported empty to the location and are not filled until they are on location. Thus, a weight limitation associated with a fully-loaded trailer is not a factor. 
     More recently, due to enhanced fracturing technology, larger volumes of fracturing fluid are required. In order to minimize the number of trailers required on location to hold the fluid, the need exists for larger capacity trailers. Unfortunately, the prior art is unable to accommodate larger volumes in view of non-permitted road width and height limitations. 
     Thus, the need exists for an design which can accommodate more volume yet satisfy the limitations associated with non-permitted road width and height limitations. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an improved mobile fluid storage tank trailer. This improved mobile fluid storage tank has a base with a front and rear end. At the front end of the base is a substantially vertical front wall and at the rear end of the base is a substantially vertical rear wall. A pair of substantially parallel vertical side walls are attached to the base and to the front and rear walls. There is a rear end roof portion extending across the rearward portion of the side walls defining a rear storage chamber and a front end roof portion extending across the forward portion defining a front storage chamber. The front and rear storage chambers are in fluid communication. The base is designed to rest on the ground once disconnected from the tractor. In this manner, the heavy load associated with stored fluid passes through the structure to the ground. The rear end roof portion is generally rectangular in shape and generally parallel with the base. The front end roof portion is a sloped section which extends from a high end at the rear end roof portion to a lower end at the front wall. The intersection of the rear and front end roof portions is selected such that the length of the rear end roof portion is preferably between about 35% and 60% of the length of the vertical side walls of the tank trailer, more preferably between about 40% and 55% of the length of the side walls, and most preferably between about 42% and 50% of the length of the side walls. In this manner, a maximum volume of fluid can be accommodated in view of the non-permitted road width and height limitations. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the invention can be obtained when the detailed description of exemplary embodiments as set forth above is reviewed in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a plan view of the top of a mobile fluid storage tank of the subject invention; 
         FIG. 2  is a plan view of one side of the storage tank of the subject invention; 
         FIG. 2A  is a partial cross-sectional view taken along line  2 A- 2 A of  FIG. 2  of the subject invention; 
         FIG. 3  is a plan view of the front end of the storage tank of the subject invention; and 
         FIG. 4  is a schematic illustration of the storage tank of the subject invention connected to a portion of a tractor vehicle for the purpose of over-the-road transport. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The mobile storage tank  10  of the instant invention, as shown in  FIGS. 1 and 2 , includes a base  12  having a front end  14  and a rear end  16 , a substantially vertical front wall  18  attached to the front end  14  of base  12  and a substantially vertical rear wall  20  attached to the rear end  16  of base  12 . A pair of substantially parallel vertical side walls  22 ,  24  are attached to base  12  and both front and rear walls  18 ,  20 . Each side wall  22 ,  24  has generally the same configuration in that it includes a flat rear portion  36  and then a sloping forward portion  40 . 
     A rear end roof portion  26  extends across the rear portion  36  of side walls  22 ,  24  defining a rear storage chamber  28  and a front end roof portion  30  which extends across the forward portion  40  defining a front storage chamber  32 . The rear and front storage chambers  28 ,  32  are in fluid communication with each other. Base  12  also includes a plurality of parallel longitudinal skids  34  that allow tank  10  to be moved along the ground when empty. Base  12  includes a wheel base having at least one axle and a plurality of wheels  35  for towing the storage tank  10  by a tractor. 
       FIG. 2A  is partial cross-sectional view taken along line  2 A- 2 A of  FIG. 2  which illustrates the “V”-shaped corrugation of front and rear walls  18 ,  20  and side walls  22 ,  24 . Referring to  FIG. 2A , each such wall panel includes a V panel  301  and a straight panel  303 . The V panels  301  are staggered between straight panels  303 . The edges of each overlap slightly and are welded together. In this manner, maximum structural rigidity is provided to support the heavy lateral loads of the drilling fluids stored within tank  10  yet maximizing the volume. Straight panel  303  is selected to be positioned at the maximum non-permitted road width and the V panel  301  then extends inwardly from that maximum non-permitted width. While the V panel  301  occupies volume, this added rigidity minimizes the loss of volume over other traditional designs. 
     As best shown in  FIGS. 1-3 , the front and rear end roof portions  26 ,  30  together define two different portions: the substantially horizontally rear portion  36  and the sloped forward portion  40 . The sloped portion  40  extends gradually downward from rear portion  36  to the front end  14  of tank  10 . The rear and front end roof portions  26 ,  30  intersect at line  38 . 
     Referring to  FIG. 4 , a key limitation associated with the transport of tank  10  by a tractor is the maximum non-permitted height of front end  14  above the ground surface. Typically, the maximum non-permitted height in the U.S. is between about 13.5 feet and 14 feet. With a typical tractor height of approximately 48 to 50 inches, this leaves about 114-120 inches for the height of front end  14 . 
     As apparent from  FIG. 2 , the location of the intersection  38  between the front and rear end roof portions  26 ,  30  is critical to ensure that the maximum non-permitted height is maintained. However, by the careful selection of the location of intersection line  38 , a maximum volume of a particular tank  10  can be achieved. To accomplish such, reference is now made to the distances “X” “Y” and “Z” as shown in  FIG. 2 . X is the length of the rear end roof portion  26 , Y is the length of front end roof portion  30 , and Z is the length of side walls  22 ,  24 . In order to achieve the maximum volume for a tank  10  in view of non-permitted maximum width and maximum height, it is preferable that the length X be between about 35% to 60% of length Z, more preferably that length X be between about 40% and 55% of the length Z, and most preferably that length X be between about 42% and 50% of length Z. For a non-permitted maximum road width of 102 inches, non-permitted maximum road height of 13.5 to 14 feet, and a length of side walls  22 ,  24  being about 503 inches, it is preferable the length of rear end roof portion  26  be between about 176 and 302 inches, more preferable that the length of a rear end roof portion  26  be between about 201 and 276 inches, and most preferably that the length of rear end roof portion  26  be between about 210 and 252 inches. 
     Referring back to  FIGS. 1 and 2 , it is also preferable that rear end roof portion  26  have an access port  100  covered by hatch  102  proximate intersection  38 . In this manner, when tank  10  is disconnected from the tractor and base  12  portion sits on the ground, port/hatch  100 ,  102  will be located at the maximum height, thereby permitting tank  10  be filled to its maximum capacity. Additionally, a rear access port  104  having a hatch  106  may be located proximate rear end  16  and a front hatch access port  108  and hatch  110  may be located proximate front end  14  to supplement in the filling and/or cleaning of the rear and forward storage chambers  28 ,  32  of tank  10 , as necessary. 
     Referring now to  FIGS. 2 and 3 , front end  14  of tank  10  may include an inclined stairway assembly  52  which is attached to front wall  18  and extends from the top of front end  14  at front end roof portion  30  adjacent sidewall  22  downwardly to second side wall  24  proximate base  12 . As illustrated in  FIG. 3 , stairwell assembly  52  generally includes a pair of upperly inclined horizontally-spaced parallel risers  54  having a plurality of vertically-spaced horizontal offset or staggered steps  56  extending between the risers in a conventional stairway construction. 
     Still referring to  FIG. 1 , the front and rear end roof portions  26 ,  28  may include a non-skid walkway or surface  200  which extends from the top of inclined stairway assembly  52  to at least port/hatch  100 ,  102 . Such provides a safe walking surface for personnel in the filling and maintenance of tank  10 . Additionally, front and rear end roof portions  26 ,  30  may include anchors  210  to which personnel may attach a harness to protect themselves from falling in the event they slip or fall during the performance of services. 
     Tank  10  may also include a side hatch or manway  212  that can be employed for gaining access to the rear and forward storage chambers  28 ,  32  for cleaning purposes or to allow persons to enter tank  10  at this location. A variety of other drains  96  can also be provided as shown in  FIG. 3 . 
     Thus, by the location of the intersection line  38 , the difference in height between front and rear end roof portions  26 ,  30  allows tank  10  to be towed via a king-end type  88  to the fifth wheel  86  of a towing vehicle  84  so that the height of tank  10  does not exceed the maximum non-permitted height permitted by law when under tow. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.