Patent Publication Number: US-2021164616-A1

Title: Support structure for cryogenic transport trailer

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/942,526 filed on Dec. 2, 2019 and entitled “Semi-Trailer Cryogenic Tank,” which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE DISCLOSURE 
     The instant disclosure relates to the transport of cryogenic materials. More specifically, portions of this disclosure relate to trailer tank designs for the transportation of cryogenic materials. 
     BACKGROUND 
     Cryogenic liquids may be stored and transported at low temperatures. For example, some cryogenic liquids may have boiling points below −130 degrees Fahrenheit and may be stored at low temperatures to maintain liquid form. One example of a cryogenic liquid, liquid Oxygen, may be transported at temperatures below −300 degrees Fahrenheit, the approximate boiling point of liquid Oxygen. As another example, liquid Argon likewise has a boiling point of approximately −300 degrees Fahrenheit and may be similarly maintained at low temperatures during transport. Other examples of cryogenic liquids may include liquid Nitrogen and liquid Helium. Environmental temperatures on Earth are far greater than the boiling points of cryogenic liquids, and thus transport structures must provide sufficient isolation between a storage unit for the cryogenic liquid and the environment during transport. Failure of the isolation structure may result in significant pressure build-up in the storage unit due to gasification of the cryogenic liquid, and possibly an explosion. Strong support structures for cryogenic transport structures may reduce the possibility of a dangerous explosion. However, the cryogenic transport structures must also meet guidelines that restrict the weight of trailers towing the cryogenic transport structure due to weight limits of road structures, such as bridges. 
     SUMMARY 
     A cryogenic transport structure, such as a dewar, mounted on a trailer and towed by a tractor, may have an outer tank and an inner tank. The inner tank may include one or more stiffeners on an outside of the inner tank along a length of the inner tank. The stiffeners may provide strength and resiliency to the cryogenic transport structure to sufficiently reduce the stresses induced by weight of the cryogenic liquids during transport. The use of such stiffeners may permit the dewar to meet or exceed certain government standards for safety and strength while maintaining and/or improving the ability of the dewar to transport an amount of cryogenic liquid. The stiffeners may allow the inner tank to have increased tensile strength without having to increase the weight of the dewar by, for example, increasing the thickness of the inner tank. The stiffeners may also permit a reduction in the overall weight of the dewar by allowing a significant reduction in the thickness of the dewar inner tank relative to the amount and weight of material added by the stiffeners. The weight limit of bridges and roads includes the weight of the structure and the weight of the cryogenic liquid. Thus, reducing the weight of the structure allows larger amounts of cryogenic liquid to be transported while remaining under the bridge and road weight limits. This reduces the cost of transporting the cryogenic liquid on a per-unit basis by allowing more cryogenic liquid to be carried in a tank. 
     In some embodiments, the cryogenic transport structure comprises a cryogenic dewar configured for transporting cryogenic liquids across roadways, such as in Canada, with at least one longitudinal stiffener attached at a top of an inner vessel of the dewar. At least one longitudinal stiffener may additionally or alternatively be attached at a bottom of the inner vessel of the dewar, for example, at a location at an opposite end of a line drawn from the at least one longitudinal stiffener (or where it would be located) attached at the top of the inner vessel and a center of the inner vessel. In some embodiments, the at least one stiffener attached to the top and/or bottom of the inner vessel comprises three or more stiffeners. When at least one longitudinal stiffener is attached at the top and bottom of the inner vessel, the longitudinal stiffeners may be attached symmetrically around the inner vessel such that each of the at least one longitudinal stiffener attached to the top is attached at a location at an opposite end of a line drawn from a corresponding longitudinal stiffener attached at the bottom and a center of the inner vessel. 
     The stiffener(s) may be attached to the outer surface of the inner vessel where the stresses on the inner vessel are the highest or significant. The inner vessel and/or longitudinal stiffener(s) may be made of steel, such as 304-grade stainless steel, or aluminum, such as 5083-grade aluminum, or another suitably strong material and may be thick enough such that, in combination, they adequately resist the stresses on the inner vessel during transport of cryogenic fluid in the inner vessel across roadways, for example, if the inner vessel forms part of a cryogenic dewar configured for use as part of a truck trailer. For example, in some embodiments, the inner vessel may be made primarily from aluminum and have a nominal thickness (i.e., an expressed but not necessarily exact thickness) of about 0.175 inches and/or the longitudinal stiffener(s) may be made from aluminum and have a nominal thickness of about 0.175 inches. 
     Such a vessel may be configured to, for example, transport about 8,200 gallons of liquid nitrogen or about 5,000 gallons of liquid argon or other amounts of cryogenic liquids. As another example, in some embodiments, the inner vessel may be made primarily from steel and have a nominal thickness of about 0.105 inches and/or the longitudinal stiffener(s) may be made from steel and have various nominal thicknesses of, for example, about 0.1054 inches, 0.165 inches, and/or about 0.135 inches. 
     In some embodiments, the thickest longitudinal stiffener or stiffeners is/are attached at the location(s) at the top of the inner vessel of highest stress, for example, caused by weight of transported cryogenic fluids within the inner vessel. In some embodiments, some or all of the longitudinal stiffeners, when attached to the outer surface of the inner vessel, do not have sufficient height to contact an outer vessel of a dewar of which the inner vessel is a part. In some embodiments, there is no solid physical path for heat to transfer from the inner dewar through the longitudinal stiffener(s) to an outer vessel of a dewar of which the inner vessel is a part. In some embodiments, the longitudinal stiffener(s) may be made primarily of material that is welding compatible with the material of the inner vessel. Welding compatibility refers to two materials that can be welded to join the two materials together. For example, steel is welding compatible to the inner vessel when the inner vessel is made from steel, and aluminum is welding compatible to the inner vessel when the inner vessel is made from aluminum. 
     In some embodiments, the inner vessel is configured to have at least one longitudinal stiffener attached to it and, when made primarily from 304-grade stainless steel, to comply with the maximum allowable tensile stress of 18,800 psi pursuant to ASME Section II, Part D, 1998 Edition, no addenda, as required by Canadian Standards Association B620 (in lieu of the 20,000 psi allowable stress under the current (as of the date of this application&#39;s filing) ASME Edition). In some embodiments, the inner vessel is configured to have at least one longitudinal stiffener attached to it and, when made primarily from 5083-grade aluminum, to comply with the maximum allowable tensile stress of 10,000 psi pursuant to ASME Section II, Part D, 1998 Edition, no addenda, as required by CSA B620 (in lieu of the 11,400 psi allowable stress under the current (as of the date of this application&#39;s filing) ASME Edition). In some embodiments, such inner vessel weighs no more than an equivalent sized inner vessel (other than material grade) configured to not include a longitudinal stiffener attached to it but that does not comply with the maximum allowable tensile stress of 18,800 psi (when made primarily from stainless steel) or the maximum allowable tensile stress of 10,000 psi (when made primarily from aluminum) pursuant to ASME Section II, Part D, 1998 Edition, no addenda, as required by CSA B620, and instead complies with only the 20,000 psi allowable stress (when made primarily from stainless steel) and the 11,400 psi allowable stress (when made primarily from aluminum) under the current (as of the date of this application&#39;s filing) ASME Edition. In some embodiments such inner vessel weighs less than an equivalent sized inner vessel (other than material grade) configured to not include a longitudinal stiffener attached to it. In some embodiments, the inner vessel configured to have at least one longitudinal stiffener attached to it has a nominal thickness at least one grade greater than the nominal thickness of the inner vessel not configured to have at least one longitudinal stiffener attached to it. In some embodiments, the inner vessel configured to have at least one longitudinal stiffener attached to it meets or exceeds governmental requirements such as, for example, the Transport Canada 341 specification standard. 
     As used in herein, the term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are “coupled” may be unitary with each other. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially parallel includes parallel), as understood by a person of ordinary skill in the art. 
     The phrase “and/or” means and or or. To illustrate, A, B, and/or C includes: A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C. In other words, “and/or” operates as an inclusive or. 
     Further, a device or system that is configured in a certain way is configured in at least that way, but it can also be configured in other ways than those specifically described. 
     The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), and “include” (and any form of include, such as “includes” and “including”) are open-ended linking verbs. As a result, an apparatus or system that “comprises,” “has,” or “includes” one or more elements possesses those one or more elements, but is not limited to possessing only those elements. Likewise, a method that “comprises,” “has,” or “includes,” one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps. 
     The foregoing has outlined rather broadly certain features and technical advantages of embodiments of the present invention in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those having ordinary skill 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 or similar purposes. It should also be realized by those having ordinary skill 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. Additional features 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 to limit the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed system and methods, reference is now made to the following descriptions taken in conjunction with the accompanying drawings. Unless otherwise noted, the features shown in each figure are to scale relative to other features in the same figure, but not necessarily relative to features in other figures including figures showing other views. 
         FIG. 1  is an example illustration of a truck hauling a trailer with a cryogenic dewar according to some embodiments of the disclosure. 
         FIGS. 2A, 2B, and 2C  are a top schematic view, bottom schematic view, and end schematic view, respectively, of an example inner vessel of a cryogenic dewar according to some embodiments of the disclosure. 
         FIGS. 2D and 2E  are enlarged views of portions of  FIG. 2C . 
         FIGS. 3A and 3B  are a top schematic view and end schematic view, respectively, of an example longitudinal stiffener according to some embodiments of the disclosure. 
         FIGS. 4A, 4B, and 4C  are a top schematic view, end schematic view, and side schematic view, respectively, of an example longitudinal stiffener cap according to some embodiments of the disclosure. 
         FIGS. 5A and 5B  are a portion of a top schematic view and an end schematic view, respectively, of an example inner vessel of a cryogenic dewar according to some embodiments of the disclosure. 
         FIG. 6  is an example method for manufacturing an inner vessel of a cryogenic dewar having at least one longitudinal stiffener according to some embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Cryogenic dewars may be used to transport cryogenic liquids, such as oxygen, nitrogen, and argon, at low temperatures. Cryogenic dewars may include a first, inner tank, mounted inside and supported by a second, outer, tank. The use of nested tanks may insulate the cryogenic liquid to help maintain low temperatures of the liquid during transport. An example illustration  100  of a cab  106  pulling a trailer  104  holding a cryogenic dewar  102  is shown in  FIG. 1 . For example, trailer  104  may include a frame that supports cryogenic dewar  102  and a means for coupling the frame to the cab  106  such as a hitch or other known means. Transportation of cryogenic liquids on Canadian roadways is regulated by a variety of statutory and regulatory provisions, such as the Transportation of Dangerous Goods (“TDG”) Act and the Commercial Vehicle Dimension and Weight Regulation of the Traffic Safety Act. Such provisions require that vehicles transporting cryogenic liquids on Canadian roadways comply with certain weight, size, and safety guidelines. For example, as of the filing of this application, section 5.10 of the TDG regulations specifies that transport containment of dangerous goods, such as cryogenic fluids, comply with certain Canadian Standards Association standards, such as CSA B620. Under Transport Canada 341 specification of CSA B620, the stress values of the inner vessel and inner support system of a dewar transporting cryogenic fluids shall not exceed:
         (a) those calculated in accordance with UG-23 and UG-54 of the ASME Code, Section VIII, Division 1;   (b) 1.25 times the maximum allowable stress value calculated in accordance with ASME Code, Section VIII, Division 1, at a temperature of 38 degrees Centigrade for the combination of general inner vessel shell stress and the local inner vessel shell stress; and   (c) the lesser of the maximum allowable stress value prescribed in ASME Code, Section VIII, Division 1 and 25% of the tensile strength of the material used.       

     In addition, CSA B620 requires that ASME, Section II, Part D, 1998 Edition (excluding addenda) will apply to these standards, which means a dewar transporting cryogenic fluids must also meet a safety factor of 4:1 for the above specifications—a higher standard than, as of the date of the filing of this application, the ASME safety factor of 3.5:1. Accordingly, a truck trailer designed for transportation under ASME standards may not meet the requirements to legally transport cryogenic fluids on a Canadian roadways. To meet these requirements, the thickness of the inner vessel could be significantly increased (whether the inner vessel is made from aluminum or steel) and/or stronger and heavier materials could be used to construct the inner vessel and/or inner vessel support system of the dewar (e.g., constructing an aluminum-designed dewar out of steel). However, each of these solutions would add significant weight to the dewar and therefore decrease the amount of cryogenic fluid the dewar could transport on a per-trip basis and increase the cost to transport an empty dewar, such as when refilling. One solution, as set forth in embodiments of this disclosure, is to include at least one stiffener attached to the inner tank of the dewar to strengthen it with little or no addition to its weight so that the stresses (e.g., bending and total) are below the required thresholds of the TC 341 standards. The stiffener(s) may be added to a reduced-thickness inner vessel of a dewar so that the overall weight of the inner vessel does not change or is even reduced while also increasing the stress resistance of the inner vessel by the additional stiffener(s) (i.e., the stiffener(s) more than offset the stress resistance afforded by a thicker inner vessel while adding less weight than the weight of such additional inner vessel thickness). 
     An example of such an inner vessel of a cryogenic dewar  1000  is shown in  FIGS. 2A-2E . The inner vessel  1000  may be made from stainless steel and include a central cylindrical section  1004  having a central axis Y and coupled at its ends by two semi-spherical ends  1008 ,  1012 . The ends  1008 ,  1012  may include, for example, a series of pipes  1024  for injecting and/or discharging fluids, such as cryogenic fluids, from inner vessel  1000 . Inner vessel  1000  may also include multiple seams  1016  (running substantially perpendicular to axis Y),  1020  (running substantially parallel to axis Y) where, for example, plates used to form inner vessel  1000  are joined (e.g., by welding). Alternatively or additionally, inner vessel  1000  may be formed from a single integral piece of material or other methods of forming vessel may be employed. 
     In order to strengthen inner vessel  1000  without significantly adding to its weight, a plurality of longitudinal stiffeners  1100  are positioned on the top and/or bottom outer surfaces of inner vessel  1000  and coupled thereto (e.g., by fastening through, for example, central openings  1128 , and/or by welding), though they could be positioned in other locations of stress in other embodiments of an inner vessel and coupled thereto. Longitudinal stiffeners increase the section modulus of inner vessel  1000 , which helps reduce stresses on inner vessel  1000 . As used herein, longitudinal means extending a length of the vessel parallel to the road surface when the vessel is in transit. Exemplary longitudinal stiffeners  1100  are shown in  FIGS. 3A and 3B . Longitudinal stiffeners  1100  may be made of stainless steel (e.g., 304-grade, as in the embodiment shown in  FIGS. 2A-2E ), or aluminum (e.g., 5083-grade, as in the embodiment shown in  FIGS. 5A and 5B ), or another suitably strong and stiff material, including, if coupled to inner vessel  1000  by welding, a material that is welding compatible with the material of the inner vessel. Longitudinal stiffeners  1100  may have an inner height IH, a thickness T, and an overall height H. Longitudinal stiffeners  1100  may have a constant inner height IH but be of different thicknesses T so that each has a different overall height H. In some embodiments, the height H of each stiffener  1100  may be less than the distance between the outer cylindrical surface of inner vessel  1000  and in the inner cylindrical surface of an outer vessel of a dewar so as to not provide a solid heat transfer path between the cryogenic fluid in inner vessel  1000  and the atmosphere outside the outer vessel of a dewar. 
     Longitudinal stiffeners  1100  may have different lengths L and be configured in multiple rows with different combinations of stiffeners  1100  (e.g., having different lengths, thicknesses, and heights) in order to optimize stress resistance relative to weight gain. For example, given that the highest tensile stresses from cryogenic fluid typically occur at the top center of inner vessel  1000  in the plane of axis Y on the side of the vessel that is furthest from the ground, two longitudinal stiffeners, such as stiffeners  1104   a , that have relatively high thicknesses T may be positioned in this location. For example, stiffeners  1104   a  have a thickness of about 0.165 inches, which is about 157% of the nominal thickness of inner vessel  1000 . The stiffeners  1104   a  are coupled (e.g., by welding or fasteners) to one another at the top center of inner vessel  1000  along the plane of axis Y and coupled on their opposite ends to other stiffeners  1116   a ,  1120   a  having relatively lower thicknesses T of about 0.1054 inches, which is about 100% of the nominal thickness of inner vessel  1000  and about 64% of the thickness of stiffeners  1104   a . Because the stresses on inner vessel  1000  are not as high at the locations of stiffeners  1116   a ,  1120   a , stiffeners  1116   a ,  1120   a  may have less thickness (and therefore also not weigh as much) as stiffeners  1104   a  located where the stresses are higher. Stiffeners  1116   a  and  1120   a  are configured to each have lengths L so that they span locations of high relative tensile stress as well as potential stress weakness such as along seams  1016 . If these seams are located at different distances from the top center of inner vessel  1000  along the plane of axis Y, the lengths of such stiffeners may be different. For example, stiffener  1116   a  has a length of about 74.25 inches, which is about 17.5% of the total longitudinal length of inner vessel  1000 , and stiffener  1120   a  has a length of about 82.25 inches, which is about 19.5% of the total longitudinal length of inner vessel  1000 . Stiffeners  1104   a  similarly span seams  1016  and have sufficient lengths to span locations of high relative tensile stress; for example, stiffeners  1104   a  each have a length of about 73.375 inches, which is about 17.5% of the total longitudinal length of inner vessel  1000 . Although examples are provided, the values may take other values for different designs while remaining in the scope of the disclosed configurations. For example, a nominal thickness of stiffeners may be between approximately 100-200% of the nominal inner vessel thickness, or more particularly between 100% and 160% of the nominal inner vessel thickness, and the longitudinal length of the stiffener may be approximately 10-100% of the inner vessel length, or more particularly between 12-20% of the inner vessel length. 
     Additional longitudinal rows of stiffeners  1100  may be positioned at other locations of high stress such as, for example, adjacent to the top center row just described. Similar to the such top center row, relatively thicker stiffeners, such as stiffeners  1108   a  (which are not as thick as stiffeners  1104   a ), may be positioned over the near-top center of inner vessel  1000  with relatively less thick stiffeners, such as stiffeners  1112   a , coupled on either end thereto. For example, stiffeners  1108   a  have a thickness T of about 0.135 inches, which is about 129% of the nominal thickness of inner vessel  1000  and about 82% of the thickness of stiffeners  1104   a , and stiffeners  1112   a  have a thickness T of about 0.1054 inches, which is about 100% of the nominal thickness of inner vessel  1000  and about 78% of the thickness of stiffeners  1108   a . Stiffeners  1108   a ,  1112   a  may have lengths sufficient to span areas of high relative tensile stress as well as potential stress weakness such as seams  1016 . For example, stiffeners  1108   a  have a length L of about 104.75 inches, which is about 24.6% of the total longitudinal length of inner vessel  1000 , and stiffeners  1112   a  each have a length of about 68 inches, which is about 16% of the total longitudinal length of inner vessel  1000 . 
     Caps  1124  are coupled (e.g., by welding or fasteners) at the end of each open end of the longitudinal rows (e.g., on an end of each of stiffeners  1112   a ,  1116   a , and  1120   a ). Caps  1124  may be made of stainless steel (e.g., 304-grade, as in the embodiment shown in  FIGS. 2A-2E ), or aluminum (e.g., 5083-grade, as in the embodiment shown in  FIGS. 5A and 5B ), or another suitably strong and stiff material, including, if coupled to inner vessel  1000  by welding, a material that is welding compatible with the material of the inner vessel. An exemplary cap  1124  is shown in  FIGS. 4A-4C  having a length EL, inner height EIH, thickness ET, and overall height EH. Caps  1124  prevent debris and other material from entering the space between the stiffeners  1100  and the outer surface of inner vessel  1000 , as shown more clearly in  FIGS. 2C-2E . 
     Referring now to  FIG. 2D , which is an enlarged view of  FIG. 2C , the various heights of the stiffeners  1100  and caps  1124  at the ends of each of the top longitudinal rows of stiffeners  1100  are shown (partially cut away in the off-center rows). As depicted, stiffeners  1108   a  have a greater overall height H than stiffeners  1112   a , stiffeners  1104   a  have a greater overall height H than stiffener  1116   a , and all stiffeners  1100  have a greater overall height H than the overall height EH of caps  1124 . 
     The bottom of inner vessel  1000  may experience significant stress similar to the stress experienced at the top of inner vessel  1000 . Accordingly, to sufficiently resist such stress, a combination of stiffeners  1100  arranged substantially the same as the combination of stiffeners  1100  at the top of inner vessel  1000  (as shown in  FIGS. 2A and 2D ), may be positioned on the outer surface of the bottom of inner vessel  1000 . One example arrangement is shown in  FIGS. 2B and 2E . Such bottom stiffeners  1100  may be substantially the same as top stiffeners  1100  and are accordingly referred to by the same reference numerals as stiffeners  1100  shown in  FIGS. 2A and 2D , except that such reference numerals end with a “b” instead of an “a” (e.g., top stiffener  1104   a  corresponds to and is substantially identical to bottom stiffener  1104   b ). As shown in  FIG. 2C , the bottom stiffeners may be positioned at opposite locations on inner vessel  1000  from the top stiffeners along a line drawn from the top stiffeners through the center Z of inner vessel  1000 . 
     The configuration of stiffeners  1100  in  FIGS. 2A-2E  is just one exemplary embodiment and other configurations are contemplated herein so long as they allow for increased stress resistance of an inner vessel. Another example configuration is shown with reference to  FIGS. 5A-5B . An inner vessel  2000  is depicted that is substantially the same as inner vessel  1000  except as otherwise stated herein. Inner vessel  2000  is made from 5083-grade aluminum, includes trunnion mounts  2012  (as shown, which may alternatively or additionally be at other locations such as an opposite end of inner vessel  2000  along axis D), and has a plurality of longitudinal stiffeners  2100 . Stiffeners  2100  are substantially the same as stiffeners  1100 , having a length L, inner height IH, thickness T, and overall height H that are sufficient to resist the stresses on inner vessel  2000  and not contact the outer vessel of a dewar when coupled (e.g., by fastening or welding) to inner vessel  2000 . In this embodiment, a single longitudinal row of two longitudinal stiffeners  2104   a  is positioned at the top center of inner vessel  2000  in the plane of central axis D (i.e., typically the location of greatest stress) and coupled together and to vessel  2000  (e.g., by fastening or welding). Stiffeners  2104   a  have a relatively large thickness of about 0.175 inches, which is about 100% of the nominal thickness of inner vessel  2000 , and are long enough (i.e., about 80 inches each, which is about 19% of the total longitudinal length of inner vessel  2000 ) to provide sufficient stiffness to inner vessel  2000  to sufficiently resist tensile stresses created by regasification of cryogenic fluids within inner vessel  2000  during transport. A cap  2124 , which is substantially the same as cap  1124 , is positioned over the open ends of the row of stiffeners  2104   a  and coupled thereto and/or to inner vessel  2000  at that location (e.g., by fasteners or welding). Similar to the embodiment shown in  FIGS. 2A-2E , the embodiment shown in  FIGS. 5A-5B  also includes a corresponding row of longitudinal stiffeners  2104   b  and caps  2124  positioned at the bottom center of inner vessel  2000  in the plane of central axis D, as partially shown in  FIG. 2B , and configured and coupled in substantially the same manner. 
     Configurations of longitudinal stiffeners  1100 , such as those shown in  FIGS. 2A-2E and 5A-5B , permit an inner vessel of a dewar such as inner vessel  1000 , that may be designed to meet lower stress requirements without the addition of longitudinal stiffeners  1100 , to meet higher stress requirements, such as those set forth in the TC 341 standard. It also permits such increased strength without having to create a new inner vessel with, for example, a greater thickness or made from a heavier material, thereby lowering manufacturing costs. Also, the addition of longitudinal stiffeners in configurations like those described herein may permit reduction in thickness and/or weight of material of a dewar inner vessel while maintaining sufficient (including legally sufficient) ability of the inner vessel to resist stresses therein. The weight of the inner vessel and therefore the weight of the dewar may also be reduced thereby to permit transport of greater loads of cryogenic fluid legally across roadways, thereby lowering transportation costs. 
     For example, in the embodiment depicted in  FIGS. 2A-2E , the inner vessel  1000  is made primarily from 304-grade stainless steel that has a nominal thickness of about 0.105 inches. The configuration of stiffeners  1100  shown in  FIGS. 2A-2E  and described above permits the inner vessel  1000  to have a maximum allowable tensile stress of 18,800 psi in compliance with ASME Section II, Part D, 1998 Edition, no addenda, as required by CSA B620, including the 4:1 safety factor, when inner vessel  1000  is part of a dewar transporting 6,000 gallons (or less) of liquid oxygen. Despite these qualities, inner vessel  1000  weighs no more than an equivalently sized (other than grade) dewar inner vessel made primarily from stainless steel that does not include the configuration of stiffeners  1100  shown and described in  FIGS. 2A-2E  and does not have a maximum allowable tensile stress of 18,800 psi in compliance with ASME Section II, Part D, 1998 Edition, no addenda, including the 4:1 safety factor, as required by CSA B620, and instead has only a maximum allowable tensile stress of 20,000 psi, with a safety factor of 3.5:1, pursuant to the current (as of the date of this application&#39;s filing) ASME Edition. Similarly, in the embodiment depicted in  FIGS. 5A and 5B , the inner vessel  2000  is made primarily from 5083-grade aluminum that has a nominal thickness of about 0.175 inches. The configuration of stiffeners  2100  shown in  FIGS. 5A and 5B  and described above permits the inner vessel  2000  to have a maximum allowable tensile stress of 10,000 psi pursuant to ASME Section II, Part D, 1998 Edition, no addenda, as required by CSA B620, including the 4:1 safety factor, when inner vessel  2000  is part of a dewar transporting 8,200 gallons (or less) of liquid nitrogen or 5,000 gallons (or less) of liquid argon. Despite these qualities, inner vessel  2000  weighs no more than an equivalently sized (other than grade) dewar inner vessel made primarily from aluminum that does not include the configuration of stiffeners  2100  shown and described in  FIGS. 5A and 5B  and that does not have a maximum allowable tensile stress of 10,000 psi in compliance with ASME Section II, Part D, 1998 Edition, no addenda, including the 4:1 safety factor, as required by CSA B620, and instead has only a maximum allowable tensile stress of 11,400 psi, with a safety factor of 3.5:1, pursuant to the current (as of the date of this application&#39;s filing) ASME Edition. 
     Such stiffener configurations similarly permit an inner vessel of a dewar to resist the same amount stresses as an equivalently-sized inner vessel made from the same type of material but weigh less, so that the stiffener-configured dewar may transport greater amounts of cryogenic fluid per trip than the non-stiffener-configured dewar to reduce shipping costs. These “increased stress-resistance” inner vessel configurations (shown and described in  FIGS. 2A-2E and 5A-5B ) and “weight reduction” inner vessel configurations are possible because the configuration of stiffeners attached to the inner vessels (e.g.,  1100  for the embodiment of  FIGS. 2A-2E and 2100  for the embodiment of  FIGS. 5A-5B ) permit increased stress resistance while allowing the inner vessels to be of a thickness at least one gauge greater than that of equivalently sized dewar inner vessels made of the same material that do not include the stiffener configurations. It is contemplated herein that such stiffeners could be employed to accomplish both increased stress-resistance and weight reduction relative to an equivalently-sized dewar without such stiffeners. 
     A method  3000  for assembling a dewar having at least one longitudinal stiffener on its outer surface is shown in  FIG. 6 . The method  3000  may begin, at step  3100 , with positioning and coupling via welding, fastening, or otherwise one or more longitudinal stiffeners to an outer surface of an inner vessel, for example, at the location(s) of the inner vessel that will experience the greatest tensile stress(es) during transport along a highway of cryogenic fluid within the inner vessel. For example, one or more stiffeners could be coupled in a row along the top center portion of the inner vessel. For example, additional stiffeners could be coupled in rows parallel and adjacent to that row. For example, one or more additional stiffeners could be coupled in a row along the bottom center portion and/or adjacent to the bottom center portion of the inner vessel at an opposite end of a line drawn from a corresponding longitudinal stiffener attached at the top and a center of the inner vessel. For example, the stiffeners could have different thicknesses and lengths and/or be made from different materials to provide optimal stress resistance while minimizing additional weight of the inner vessel. 
     At step  3200 , the method  3000  may continue with positioning and coupling via welding, fastening, or otherwise one or more caps to one or more ends of the stiffener(s). For example, a cap may be coupled to the end of a stiffener such that a gap formed between the stiffener and the outer surface of the inner vessel is not accessible, including to debris or other materials. 
     At step  3000 , the method  3000  may continue with positioning and securing the inner vessel having the longitudinal stiffener(s) and cap(s) within an outer vessel of a dewar. For example, the inner vessel may be secured to the outer vessel of the dewar such that the longitudinal stiffener(s) and cap(s) do not contact the outer vessel. 
     The schematic flow chart diagram of  FIG. 6  is generally set forth as a logical flow chart diagram. Likewise, other operations for the circuitry are described without flow charts herein as sequences of ordered steps. The depicted order, labeled steps, and described operations are indicative of aspects of methods of the invention. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagram, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. 
     Although the present disclosure and certain representative 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 disclosure 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 present disclosure, 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. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.