Intermodal container tank construction

There is provided an intermodal container tank construction wherein the tank vessel is connected to and supported on the respective structural end frames by respective connecting systems. Each connecting system includes a space frame structure interconnecting a circumferential ring stiffener positioned near a tank vessel end to a respective end frame. The space frame structure includes left and right vertical trusses connecting the left and right sides of the end frame to the respective lateral sides of the ring stiffener and top and bottom horizontal trusses connecting the top and bottom of the end frame to the respective top and bottom of the ring stiffener. The trusses transfer all vertical and horizontal loads on the tank vessel to the corner fittings of the front and rear end frames.

The present invention relates generally to intermodal container tanks such 
as employed in land, sea and air transportation of bulk liquids and other 
bulk materials with fluid like characteristics and, more particularly, it 
relates to an improved construction for such container tanks which is more 
efficient than intermodal container tank constructions employed heretofor. 
Intermodal container tanks generally consist of two types, namely, the full 
frame type and the beam type. The frame type intermodal container tank 
comprises a generally cylindrically shaped tank closed by end caps which 
are generally convexly shaped and vertical, transversely arranged 
rectangular end frames which are interconnected by longitudinal structural 
members so as to provide structural integrity for the container tank. The 
tank itself may be securely supported within this frame structure by means 
of cradles or saddles and/or other bearer members in order to transfer the 
container tank load to the frame structure. Examples of such frame type 
container tanks can be found in U.S. Pat. No. 4,354,612, to Pelabon, 
granted Oct. 19, 1982 and U.S. Pat. No. 4,416,384, to Bjurling, granted 
Nov. 22, 1983. 
In the beam type intermodal container tank, the tank itself serves as a 
structural member connecting the structural end frames. The end frames are 
themselves connected to the tank by means of structural bearer members 
which transfer the container tank load to the end frames. As in the case 
of the frame type container tank, the tank of the beam type is generally 
cylindrically shaped having its ends closed by generally convexly shaped 
end caps. The end frames are vertical, transversely arranged rectangular 
structures dimensioned to be approximately equal to the tank diameter or 
slightly larger. 
An example of a beam type intermodal container tank can be found in U.S. 
Pat. No. 5,083,673, to Fossey, granted Jan. 28, 1992. The Fossey patent 
discloses a tank vessel which is connected to each of its respective 
rectangular end frames by mounting means comprising two upper and two 
lower bearer members arranged at a 90.degree. interval with respect to 
each other and at 45.degree. with respect to a vertical line passing 
through the tank diameter. In one embodiment, all four bearer members are 
identical and consist of a bearer plate extending longitudinally from tank 
to end frame, being curved at the tank connection to conform to the tank 
curvature and welded thereto adjacent to the weld seam of the end cap, 
i.e. the head knuckle radius. At the end frame, the bearer plate is welded 
to a corner connecting member which extends between a frame side member 
and the adjacent cross member. In another embodiment, one which is used 
commercially, the lower bearer members each comprise a generally 
triangularly shaped boxed section arranged radially with respect to the 
tank and connected to the tank at about the head knuckle radius through 
supporting side flanges welded to the tank. The bearer member is then 
connected to the end frame between the middle of the corner connecting 
member and the respective corner of the end frame. 
Intermodal container tanks are designed and fabricated to meet recognized 
standards, such as promulgated by the International Organization for 
Standardization (ISO), U.S. Department of Transportation (D.O.T.), 
International Maritime organization (IMO), American Society of Mechanical 
Engineers (ASME) and similar organizational bodies. Specifically, the U.S. 
D.O.T. regulations limit the maximum gross weight of such container tanks 
transported over U.S. highways. Thus, the unladen weight or tare weight of 
the intermodal container tank is an important factor affecting the amount 
of material which can be shipped in the container tank. Intermodal 
container tank constructions heretofor employed result in container tanks 
which are unnecessarily heavy because of structural considerations 
relating to the tank to frame connection methods used. This added tare 
weight reduces the allowable cargo weight while increasing handling and 
transportation costs. 
Furthermore, especially in connection with beam type intermodal container 
tank constructions, as typified by the hereinabove described Fossey 
patent, the structural bearer members connecting the lower part of the 
tank to the structural end frames are relatively rigid because of the 
geometric shapes required for the connections. Thus, since such bearer 
members are generally attached to the tank proper in the immediate area of 
the head knuckle radius, the relative rigidity of the bearer members and 
the relatively thin plate of the tank vessel result in additional stresses 
being introduced into the thin plate of the tank and its head or end cap 
at the critical head knuckle radius. 
Yet another disadvantage inherent in intermodal container tank 
constructions employed heretofor relates to structural damage sustained by 
the structural bearer members and end frames during handling. Any such 
structural damage requires that the container tank be taken out-of service 
for a substantial period of time so that repairs can be effected at a 
qualified repair shop. In addition, fabrication of current intermodal 
container tanks is, in many cases, difficult and inefficient because of 
the complex and often ponderous designs employed, thus requiring added 
fabrication labor which is reflected in the cost of the container tanks. 
It is, therefore, a primary object of the present invention to provide an 
intermodal container tank construction, particularly of the beam type 
container tank, which results in an intermodal container tank which has a 
lighter tare weight, minimizes stresses in the tank shell, employs a 
simple design and can be more easily repaired than intermodal container 
tanks heretofor. 
The above object, as well as others, which will hereinafter become 
apparent, is accomplished in accordance with the present invention by the 
provision of a novel tank to end frame connection system which employs a 
truss framework connected between the extreme circumferential ring 
stiffener nearest each tank end and the respective structural end frame. 
Circumferential ring stiffeners are required for most if not all 
intermodal container tank constructions to compensate for any negative 
internal tank pressures resulting from an external over pressure. By 
connecting the truss framework to the required circumferential ring 
stiffeners rather than directly to the tank, the tank forces resulting 
from tank and cargo weights and acceleration forces during transit bypass 
the tank proper and are transmitted directly to the extreme 
circumferential ring stiffeners and thence through the truss framework to 
the support points in the structural end frames. Thus, additional stresses 
resulting from out-of-plane bending on the already stressed tank proper, 
especially in the head knuckle radius, near the welded connection of the 
tank end to the tank shell, are minimized. 
The truss framework, which efficiently transmits tank loads to the end 
frames, consists of eight bearer members connected to each end frame and 
arranged in pairs to surround the tank proper on its four longitudinal 
sides, left, right, top and bottom. Each pair of truss members is 
connected to a longitudinal side of the extreme circumferential ring 
stiffener at a common point and each truss member runs therefrom at 
substantially a 45.degree. angle to the respective vertical or horizontal 
column of the end frame, which also constitute truss members, and attaches 
thereto near the corner casting or fitting. A truss member is designed to 
carry axial loads so that the entire cross-sectional area of the member is 
either in tension or compression. Thus, the load paths for loads 
transmitted by the tank to the end frames are as follows: longitudinal 
tank loads are transmitted to the end frames by all the truss members 
connected to the tank; vertical tank loads are transmitted to the end 
frames by the truss members connected to the tank in the two vertical 
longitudinal planes, i.e. left and right sides, of the tank (the truss 
members connected to the tank in the two horizontal longitudinal planes, 
i.e top and bottom, of the tank are ineffective for vertical loads); 
transverse tank loads are transmitted to the end frames by the truss 
members connected to the tank in the two horizontal longitudinal planes, 
i.e. top and bottom of the tank (the truss members connected to the tank 
in the two vertical longitudinal planes, i.e. left and right sides of the 
tank are ineffective for transverse loads). 
In another embodiment of the present invention, the truss framework of 
eight bearer members are connected in pairs at a common point on the 
circumferential ring stiffener at 45.degree. to the vertical and 
horizontal diametric planes of the tank and extend therefrom at 
substantially a 45.degree. angle to substantially the centers of adjacent 
horizontal and vertical columns of the respective end frame. In this 
embodiment, the adjacent one half of the horizontal and vertical columns 
of the end frame in effect constitute the remaining truss member of each 
truss.

Now turning to the drawings, there is shown in FIG. 1 a beam type 
intermodal container tank, generally designated 10, including a generally 
cylindrically shaped tank vessel (shown in phantom for purposes of 
clarity), designated 12, a rear structural end frame, designated 14, a 
substantially identical opposing front structural end frame, designated 
16, a rear circumferential stiffening ring, designated 18, a front 
circumferential stiffening ring, designated 20, at least one intermediate 
circumferential stiffening ring, designated 22, a rear connecting system 
24 connecting rear end frame 14 to tank 12 and a front connecting system 
26 connecting front end frame 16 to tank 12. 
Rear structural end frame 14 is disposed near to the rear or discharge end 
of tank 12 and includes horizontal top and bottom rails, respectively 
designated 28 and 30, vertical left and right corner posts, respectively 
designated 32 and 34, four identical corner fittings, designated 36, 38, 
40 and 42, respectively, and four identical diagonal corner braces 44. 
Front structural end frame 16 is substantially identical to rear end frame 
14 and disposed near to the front end of tank 12. Commonly, a structural 
end frame, such as end frames 14 and 16 herein, is dimensioned slightly 
larger than the tank it is connected to in order to protect the adjacent 
tank head or end and the tank vessel itself. The corner fittings are 
standardized throughout the industry and permit the stacking of a 
plurality of intermodal container tanks for shipping purposes and the 
handling of such tanks by specialized equipment. 
Rear circumferential stiffening ring 18 is identical to front 
circumferential stiffening ring 20 and consists of a metal channel welded 
to the exterior of tank vessel 12 for structural support and strengthening 
of the shell of tank 12. One or a plurality of similarly constructed 
intermediate circumferential stiffening rings 22 may be arranged on tank 
12 between front and rear stiffening rings 20 and 18. Rear stiffening ring 
18 is positioned on tank 12 near the welded connection of the tank head or 
end to the tank itself. Front stiffening ring 20 is similarly positioned 
at the opposing end of tank 12. 
Rear connecting system 24 is substantially identical to front connecting 
system 26 and, as clearly seen in FIG. 2, interconnects end frame 14 and 
rear stiffening ring 18. Novel front and rear connecting systems 26 and 24 
are constituted to fully structurally support tank 12 on end frames 14 and 
16 without the need for additional structural supporting elements. 
Connecting system 24 consists essentially of a space frame structure 
wherein right vertical truss 46 connects the right side of end frame 14 to 
the right lateral side of stiffening ring 18, left vertical truss 48 
connects the left side of end frame 14 to the left lateral side of 
stiffening ring 18, top horizontal truss 50 connects the top of end frame 
14 to the top of stiffening ring 18 and bottom horizontal truss 52 
connects the bottom of end frame 14 to the bottom of stiffening ring 18. 
Right vertical truss 46 consists of a member 54 connected to corner post 
34 at the bottom thereof near bottom corner fitting 36 and a member 56 
connected to corner post 34 at the top thereof near top corner fitting 38. 
Thus, corner post 34 also forms one of the truss members of right vertical 
truss 46. Truss members 54 and 56 run upwardly and downwardly, 
respectively, from corner post 34 at an approximately 45.degree. angle to 
converge and meet at the right lateral side at about the center of 
stiffening ring 18. Left vertical truss 48 consists of a member 58 
connected to corner post 32 at the bottom thereof near bottom corner 
fitting 42 and a member 60 connected to corner post 32 at the top therof 
near top corner fitting 40. Thus, corner post 32 also forms one of the 
truss members of left vertical truss 48. Truss members 58 and 60 run 
upwardly and downwardly, respectively, from corner post 32 at an 
approximately 45.degree. angle to converge and meet at the left lateral 
side at about the center of stiffening ring 18. Top horizontal truss 50 
consists of a member 62 connected to horizontal top rail 28 at the right 
side thereof near top corner fitting 38 and a member 64 connected to 
horizontal top rail 28 at the left side thereof near top corner fitting 
40. Thus, horizontal top rail 28 forms one of the truss members of top 
horizontal truss 50. Truss members 62 and 64 run from the respective sides 
of horizontal top rail 28 at an approximately 45.degree. angle to converge 
and meet at about the center of the top of stiffening ring 18. Bottom 
horizontal truss 52 consists of a member 66 connected to horizontal bottom 
rail 30 at the left side thereof near bottom corner fitting 42 and a 
member 68 connected to horizontal bottom rail 30 at the right side thereof 
near bottom corner fitting 36. Thus, horizontal bottom rail 30 forms one 
of the truss membes of bottom horizontal truss 52. Truss members 66 and 68 
run from the respective sides of horizontal bottom rail 30 at an 
approximately 45.degree. angle to converge and meet at about the center of 
the bottom of stiffening ring 18. 
The space frame connecting system hereinabove described, connecting the end 
frames to the respective stiffening rings, effectively transfers all 
horizontal and vertical tank loads to the end frame and thus the corner 
fittings which support the intermodal container tank during shipping and 
handling. Furthermore, in the event of damage to one or more of the truss 
members of the space frame connecting system, resulting from collisions or 
other accidents, it is a relatively easy matter to replace the damaged 
truss member which, in many cases can be accomplished on site without 
removal of the container tank to a repair shop. 
As clearly seen in FIGS. 3 and 4, the individual truss members of trusses 
46, 48, 50 and 52 may be formed of either round or rectangular pipe or 
tubing. Preferably, round pipe is used inasmuch as round pipe has a 
constant inertia throughout its length whereas the inertia is variable in 
rectangular pipe or tubing. In addition, torsion induces additional 
stresses in rectangular pipe but not in round pipe. 
In FIGS. 5 to 16, different methods of connecting the individual truss 
members to the ring stiffeners and end frames are shown. In FIGS. 5 and 6, 
truss members 62 and 64 of top horizontal truss 50 are welded at their 
ends to the side of a channel section saddle sleeve 70 which overlies ring 
stiffener 18. Saddle sleeve 70 is bolted to ring stiffener 18 by bolts 72 
which pass through both sides of saddle sleeve 70 and the channel of ring 
stiffener 18. Ring stiffener 18 may be strengthened at the bolted 
connection by a spacer sleeve 74 disposed between the sides of ring 
stiffener 18 at the bolt holes through which bolt 72 passes. By bolting 
overlying channel 70 at both sides of ring stiffener 18, the attachment is 
stronger than if only one side of ring stiffener 18 were bolted. 
FIGS. 7 to 9 show two methods of attaching truss members to an end frame. 
In FIG. 7, truss members 60 and 64 are shown to be welded to corner post 
32 and horizontal top rail 28 of end frame 14, respectively. In FIG. 8, 
truss members are shown to be bolted to the end frame. Bolting the truss 
members to the end frame has the advantage that bolting takes out most 
bending momemts in the truss members since the bolted connection performs 
like a hinge. The bolted connection allows truss members of a smaller 
thickness to be utilized than in the case of the welded connection. As 
clearly seen in FIGS. 8 and 9, the end of each truss member, for example 
truss members 60 and 64, has inserted therein and welded thereto a pair of 
parallel ears, designated 76 and 78, while the respective end frame 
member, for example corner post 32 and horizontal top rail 28, has a 
single ear 80 inserted therethrough and welded. Single ear 80 is 
sandwiched between forked parallel ears 76 and 78 and bolted thereto by 
nut and bolt 82 to form a clevis type connection. 
FIGS. 10 and 11 show another method of truss member connection to ring 
stiffener 18. Thus, the tank connection ends 84 of truss members 62 and 64 
of top horizontal truss 50 are deformed as by flattening or tapering and 
the end tip welded to the side of ring stiffener 28. In order to transmit 
the stresses to both sides of ring stiffener 18, a connection plate 86 is 
welded on the inside of the channel structure of ring stiffener 18 at the 
point of connection of the truss member. 
FIGS. 12 to 16 show another example of a truss member to ring stiffener 18 
connection method. In this connection method, the tank connection ends 88 
of truss members 62 and 64 of top horizontal truss 50 are partially 
cut-out at 90 to overlap ring stiffener 18 and welded thereto. As clearly 
seen, the ends 88 of truss members 62 and 64 are adapted to meet and are 
welded together as well as to ring stiffener 18 for greater strength. 
Alternatively, the ends 88 of the truss members may be spaced from each 
other and welded to ring stiffener 18. 
FIG. 17 shows a second embodiment of the tank to end frame connecting 
system of the present invention. Therein, tank vessel 112 provided with 
rear circumferential stiffening ring 118 and front circumferential 
stiffening ring 120 is connected to rear end frame 114 and front end frame 
116 by rear connecting system 124 and front connecting system 126, 
respectively. Rear connecting system 124 is substantially identical to 
front connecting system 126 and, as clearly seen in FIG. 18, its four 
trusses 146, 148, 150 and 152 are connected to rear stiffening ring 118 at 
points which are 45.degree. to the horizontal and vertical diametric 
planes of tank vessel 112. Truss members 154 and 156 of truss 146 extend 
from their common connection at ring stiffener 118 at substantially 
45.degree. to each other to the center point of right corner post 134 and 
the center point of horizontal top rail 128, respectively, of end frame 
114. Thus, the adjacent one half sections of right corner post 134 and 
horizontal top rail 128 together form a truss member of truss 146. 
Similarly, truss members 158 and 160 of truss 148 extend from their common 
connection at stiffening ring 118 to the center points of horizontal 
bottom rail 130 and left corner post 132, respectively. Truss members 162 
and 164 of truss 150 extend from their common connection at stiffening 
ring 118 to the center points of horizontal top rail 128 and left corner 
post 132, respectively. Truss members 166 and 168 of truss 152 extend from 
their common connection at stiffening ring 118 to the center points of 
horizontal bottom rail 130 and right corner post 134, respectively. 
Connecting systems 124 and 126, connecting end frames 114 and 116 to 
circumferential ring stiffeners 118 and 120, respectively, effectively 
transfers all horizontal and vertical tank loads to the horizontal rails 
and corner posts of the end frames and thus the corner fittings which 
support the intermodal container tank during shipping and handling. 
Although the above general and detailed descriptions relate the present 
invention to use with a beam type intermodal container tank, it is 
possible to utilize the same with the full frame type intermodal container 
tank wherein longitudinal beams connect the corner fittings of the front 
and rear end frames. It is also possible to strengthen the beam type 
intermodal container tank utilizing the present invention by the addition 
of longitudinal braces connected between the end ring stiffeners and the 
intermediate ring stiffeners. Such braces are attached to the end ring 
stiffeners at about the connection thereto of the vertical and horizontal 
trusses. 
It is to be understood that the foregoing general and detailed descriptions 
are explanatory of the present invention and are not to be construed as 
restrictive of the scope of the following claims.