US3780903A

US3780903A - Corner construction for reinforcing rib on tank made from thin sheet metal

Info

Publication number: US3780903A
Application number: US00274322A
Authority: US
Inventors: E Clarkin; G Conlee
Original assignee: Nooter Corp
Current assignee: Nooter Corp
Priority date: 1972-07-24
Filing date: 1972-07-24
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25

Abstract

The corner between adjacent ends of reinforcing ribs on adjacent walls of a tank is fabricated from two outer members which are assembled as a unit. The corner unit is then connected between the ribs on the adjacent angularly positioned walls by welding it into place to form the complete corner. One of the ends of an outer member is preferably offset inwardly so as to fit within one cooperating rib for ease in assembling and welding.

Description

United States Patent [191 Clarkin et al.

[ CORNER CONSTRUCTION FOR REINFORCING RIB ON TANK MADE FROM THIN SHEET METAL [75] Inventors: Edward J. Clarkin, Florissant;

George D. Conlee, Glendale, both of [73] Assignee: Nooter Corporation, St. Louis, Mo.

[22] Filed: July 24, 1972 [2l] Appl. No.: 274,322

[52] US. Cl. 220/71, 220/73 [5|] Int. Cl B65d 7/42 [58] Field of Search 220/71, 62, 74, 75,

[56] References Cited UNITED STATES PATENTS 2,675,940 4/1954 Schmitz 220/71 2,360,218 l0/l944 Gavin ..220/62 Dec. 25, 1973 3,025,995 3/1962 Koelsch et al. 220/71 2,337,049 12/1943 Jackson 220/75 3,024,942 3/1962 Schmitz 220/71 675,029 5/1901 Walborg et al. 220/73 2,205,826 6/1940 Small 220/75 Primary Examiner-William T. Dixson, Jr. Assistant Examiner-Allan N. Shoap' Attorney-Roy A. Lieder et al.

[5 7] ABSTRACT The corner between adjacent ends of reinforcing ribs on adjacent walls of a tank is fabricated from two outer members which are assembled as a unit. The corner unit is then connected between the ribs on the adjacent angularly positioned walls by welding it into place to form the complete corner. One of the ends of an outer member is preferably offset inwardly so as to fit within one cooperating rib for ease in assembling and welding.

9 Claims, 10 Drawing Figures SHEET 30F 4 PATENTEU DEC 25 #975 PATENTEU DEC 2 5 I975 SHEET 0F 4 FIGJO CORNER CONSTRUCTION FOR REINFORCING RIB ON TANK MADE FROM THIN SHEET METAL This invention relates to an improved corner construction for ribs on tanks, and more particularly, to a corner construction and process for making same as applied to fermenter tanks used in the brewing industry. As used herein, the word tank includes tanks for processing or storage or any other purpose.

The present invention is an improvement on the corner of a fermenter tank of the type shown in Schwaiger US. Pat. No. 2,823,125 granted in 1958, which is a complete enclosure fabricated from flat and relatively thin stainless'steel.

At present, stainless steel fermenter tanks are often used in the brewing industry, especially in new breweries. One such fermenter tank is shown in said Schwaiger patent. Years ago these fermenter tanks were built with a capacity of about 400 barrels of beer, and were about 2l feet long, 12 feet wide, and 8 feet high. A barrel of beer contains about 31 gallons. However, at the present time, such fermenter tanks of the type referred to are about 56 feet long 12 feet wide, and feet high. The slope of the roof or top wall is substantially the same as in the smaller tanks. Such a fermenter tank holds about 1539 barrels of beer gross when it is completely filled, and about I426 barrels of beer net when it holds the proper amount for fermentation.

As explained in the Schwaiger patent, the top wall and perhaps the bottom wall are not truly horizontal but slope to enable the fermenter tank to operate properly and be cleaned. The top wall may deviate several degrees from a true horizontal plane. As a result, the angle between the top wall and the vertical walls may not be exactly 90 in fermenter tanks of this type, so any reference to 90 herein is only approximate where the angle between a substantially horizontal wall and a vertical wall deviates from a true 90. Exact angles are not mentioned herein since they may differ at different parts of the tank and may be either slightly more or less than 90, as well as a true 90. Likewise, reference to 45 is-approximate depending upon the true angle of which it bisects.

Fermenter tanks of the type described are made from flat sheets of stainlesssteel, Type 304, which has a chromium content of 18 to 20percent and a nickel content of 8 to l2percent. In fermenters of this size, 12 gauge material is used and gives satisfactory results. In the past, the corners of the tank were rounded and the corners of the reinforcing ribs were rounded, or more precisely, were quadrants of a circle connecting the substantially horizontal ribs on the top and bottom walls with the vertical ribs on the side walls. These rounded corners were difficult to fabricate and required all the welding to be done on the tank location from the outside of the rounded corner, with what is known as outside drop-through welding.

One of the principal objects of the present invention is to provide a corner for joining reinforcing ribs on adjacent walls, which corner is easy to fabricate, which can be butt welded from the inside and outside to give a through penetration weld, and which can be formed as a unit and then connected between the registering reinforcing ribs which it is to connect and welded into place. Another object is to provide a corner which is at least as strong as the cornerheretofore used for fermenter tanks of the type described and for other thin walled tanks. Another object is to provide a corner made from only two outer pieces of sheet metal rather than the several pieces heretofore used. Another object is to provide a corner with through penetration welds which can be made as a unit in a fixture and then transported to the place where it is to connect the angularly positioned reinforcing ribs. These and other objects and advantages will become apparent hereinafter.

The invention is embodied in a corner construction for tanks and in the process for forming said corner. The invention is further embodied in a square corner which can be fabricated conveniently on the shop floor in a fixture as a unit before it is transported to the corner of a tank, which tank corner may be in an elevated or difficult position on which to work. The invention is further embodied in the process for making said square corner for the tank.

The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed, and further consists in the process 1 of making said corner. In the accompanying drawings, which form part of this specification and wherein like numerals and symbols refer to like parts wherever they occur:

FIG. 1 is a side elevational view of a tank showing reinforcing ribs therearound,

FIG. 2 is an end view ofa tank showing a reinforcing rib encircling said tank, said tank rib having corners embodying the present invention,

FIG. 3 is an enlarged fragmentary perspective view of a prior art corner made from separate pieces which are welded together on the site,

FIG. 4 is a view looking directly at said prior art corner froma position 45 with respect to the top wall and side wall,

FIG. 5 is an enlarged fragmentary view of a new upper corner embodying the present invention,

FIG. 6 is an enlarged view of said corner itself look- 7 ing at an angle of 45 with respect to the top wall and side wall,

FIG. 7 is a fragmentary perspective view showing the top rib and side rib of a tank ready to receive a corner embodying the present invention,

FIG. 8 is a perspective view of said corner prior toinstallation,

FIG. 9 is an exploded perspective view of a bottom corner embodying the present invention and ready for installation at the bottom corner of a tank to connect the vertical rib with the bottom rib, and

FIG. 10 is a cross-sectional view along the line l010 of FIG. 9.

Referring now to the drawings in detail it will be seen that the embodiment of the invention is shown in a tank T which may be a'fermenter tank for holding beer.

These fermenter tanks T are large and contain a great weight of liquid and retain a small amount of pressure.

The sheet metal used in the walls W of the tank is as thin as possible inorder to reduce cost and weight. The thin wall material must be reinforced at spaced intervals by reinforcing. r'ibs R. These ribs R completely encircle the tank T along the top wall 1, side walls 2 and usually supported on a support or frame F comprising four longitudinally extending I-beams 6 on which the reinforcing ribs R on the bottom wall 4 rest. These four longitudinal I-beams 6 in turn are supported on larger cross beams, which may be supported on the floor of a brewery. In the case of newer breweries, the cross beams may be connected directly between the vertical beams which support the building. In practice, the reinforcing ribs R on the bottom wall 4 contain vertical gussets therein at a point above the middle of each longitudinal I-beam for strength purposes.

Each reinforcing rib R may be made from the same kind and thickness of material as the walls W of the tank T. This prevents problems in welding and those resulting from different coefficients of expansion. Each reinforcing rib R has a cross-section of generally inverted modified U shape (FIG. 7) and has an outer portion 7 parallel to the wall W with two sloping sides 8 extending angularly therefrom toward the wall W of the tank T withflanges 9 extending parallel to the outer portion 7 and to the wall W. Thus, each reinforcing rib R has five flat portions, including the outer portion 7, two sides 8, and two flanges 9. The flanges 9 of each rib R are connected to the wall W of the tank T, usually by spot welds 10. The ribs R are spaced at intervals, which vary according to the thickness of the walls, the dimensions or sizeof the tank, and the amount of weight the tank is to hold. In a fermenter tank, the ribs R may be spaced apart, for example, a distance of about 16 inches from rib center to ribcenter. The ribs R on the top, side, and bottom walls W of the tank are spaced in parallel and registering relation, so that when they are connected at or around the corners C of the tank, a completely encircling rib R is formed. This encircling rib R structure gives greater strength for the amount of material used. In tanks of this type, the corners C between adjacent walls W are rounded, usually on about a 2inches radius.

Referring to FIG. 7, a top rib 11 is shown with its open end 12 terminating slightly short'of the curved upper tank corner C of the tank T, and a vertical side rib 13 is shown welded to the side wall 2 of the tank with its-open end or edge 14 terminating just at or below the startof the curvature of the upper tank corner C. The top wall 1 and side wall 2-are connected by means ofa horizontal weld 15 near the top'of the tank. The outer or free edge 12 of the top rib 11 is preferably at right angles to thetop wall 1, or substantially vertical. The upper or free edge 14 of the side'rib 13 is at right angles to the side wall 2, or substantially horizontal. These two

free edges

12 and 14 are therefore substantially perpendicular to each other and are in a position in FIG. 7 for receiving a corner or corner rib K which connects the two. In tanks where the top 'wall 1 and side wall 2 are at 90, then these

edges

12 and 14 will be truly perpendicular to each other. However, if the top wall 1 slopes slightly, they will not be truly perpendicular.

In the past, the corner K between the ribs R was formed from four separate pieces (FIG. 4) which had to be welded in place (in situ) on the tank (FIG. 7). This meant that a workman had to work at least feet off of the ground in order to fabricate the top corners K, or was working near the ground but in an awkward, almost upside down position, while fabricating the bottom corners K. To form the corners K shown in FIGS. 3 and 4, workmen would first weld a curved piece or flange 16 which formed the two flanges 16 around the tank cornerC in order to connect the flanges 9 of a horizontal rib, such as the top rib 11, and avertical rib, such as the side rib 13. He would then tack weld a curved side 17 to one flange 16, then tack weld a curved outer portion 18 to the curved side 17 and to the outerportions of the horizontal top rib 1 1 and vertical side rib l3, and then tack weld or weld the other curved side 19in position between the outer portion 18 of the corner and the corner flange 16. He would then drop-through weld all of the seams which had previously been tack welded in order to form the corner. Drop-through welding is welding from the outside or one side of the material sufficiently deep so that the weld starts to drop through on the other side, thereby insuring a weld completely through the material. Experience and know-how dictate the conditions and quality of such welding. The curved outer portion 18 was usually made from thicker material than the other portions of the corner K, ribs R, or walls W.

Thus, the curved prior art corner K shown in FIG. 3 is a corner fabricated in situ at the location from at least four separate

outer pieces

16, 17, 1 8, and 19, which were welded together in place from one side of the material. These pieces were welded to each other and to the horizontal and vertical ribs, which they connected, in place at the location on the tank where the corner was needed whether that was close to the floor or high in the air. In tanks having 42 encircling ribs, this meant forming 168 such corners in difficult and inconvenient positions. 1

The corners L (FIGS. 5-10) embodying the present invention are made from two outer members or pieces of

material

20 and 21 which form half portions of the corner. Each half portion is folded, as at. 22, to form one piece and initially contains no welds whatever. These two half portions are connected by a central weld 23 along a line and across the apex 24 to form the 90 corner L. Each half portion or

outer member

20 and 21 has an outer portion 7 and two sides 8 which register with the corresponding portions of the ribs R.

A stiffener or corner gusset 25 is welded within the outer portion of the corner L at an angle of 45 with its outer edge 26 welded along the apex-24 of the corner L and its inner edge 27 spaced from the tank corner C. The corner gusset is made of carbon steel and is about 1 /2 times the thickness of the sheet metal used in the tank wall W and reinforcing ribs R. The corner gusset 25 is approximately three-eighths inches thick and is provided with a hole 28 for drainage purposes. One member of the corner L contains a joggle joint or offset portion 29 along its upper and side edges, so' that it can be slipped into the end of a reinforcing rib R. At the top corners, it is optional whether the offset portion is slipped into a horizontal rib ora vertical rib. However, at the bottom, the offset portion is slipped into a vertical rib so that a vertical gusset can be used as a backup for the weld and-to provide extra strength for the bottom ribs which rest on the I-beams 6. The square corner L has

outer portions

20 and 21 which are in corner to corner relation and are connected by a fillet weld at the apex 24 thereof. The corner gusset 25 has chamfered portions along its outermost edges so as to flatly contact the inrr er faces of the

outer portions

20 and 21 of the square corner. Fillet welds are provided between the gusset 25 and the

outer portions

20 and 21. The gusset 25 is weldedto the corner L adjacent to the central weld 23 for strength purposes. The corner gusset 25 extends atleast half the distance from the apex 24 inwardly along the central weld 23 toward the tank corner C.

The entire corner L shown in FIGS. 8 and 9 may be prefabricated in a special fixture or jig or may be fabricated on the floor or on a table. The corner L is then transported as a unitto the upper or lower corner C of the tank to connect the top ribs 11 with the side ribs 13 and the bottom ribs 30 with the side ribs 13. This is accomplished by placing the joggle joint within the side rib 13 until the recessed portion 29 is completely within the side rib 13. Some movement is present to allow for slight adjustment and alignment of the other half portion with the top rib 11 or bottom rib 30.

Prior to applying the corner L (FIG. 8), the top rib 11 is provided with a butt strap 31 which is a three sided piece of material which fits half into the top rib 11 and corner L. The butt strap 31 is tack welded into the rib 11 prior to the application of the corner L in both the old corner K (FIG. 3) and new corner L (FIGS. 5-10). The butt strap 31 is tack welded to'the sloping sides 8 of the top rib l1, and to the outer portion 7 of the rib 11.

After the corner L (FIG. 8) has been placed into position with the offset portion 29 slipped within the side rib l3 and with its opposite end or upper edge slipped over the butt strap 31, this unitary corner unit L can be welded in place by butt welds where it meets the top rib 11 and side rib 13, so that the outer portions 7 and the sides 8 are in edgewise abutting relation. The corner L is also welded along the curved corner C of the tank along its curved inner edge 32 by a fillet weld.

Thus, the new corner is made from two outer members which are welded together to form a unit which is then transported to the location between the horizontal and vertical ribs. In the past, four pieces were required to be welded to each other and to the vertical and horizontal ribs by a welder who necessarily had to assume an awkward position. The new' comer (FIG. 8) readily permits a heavy gusset or stiffener to be assembled into the outermost portion of the corner to give further rigidity thereto.

The identical new corner L is also used as a lower corner, as shown in FIG. 9. When so used, the bottom rib is provided with a vertical gusset-33 in the free open end 34 thereof. Each vertical gusset 33 has a weep hole or vertical slot 35 therein to permit drainage in the remote event that moistureor liquid gets into the bottom rib 30. Under normal conditions, no liquid'is intended to ever get into any reinforcing rib, but drainage means are provided in the event that leakage should occur. The drainage system not only keeps the reinforcing ribs and corners free of liquid, but immediately notifies the operator that a leak is occurring in the tank. The lowest part of the outer portion 7 of the lowermost bottom corner L is provided with a weep hole for allowing any leakage to escape from a rib R. The vertical gusset 33 is made from approximately the same thickness of material as the corner gusset 25 and is of trapezoidal shape and fully occupies the open end 34 of the bottom rib 30 at a point directly above the center of the longitudinal I-beam supports 6. This gives further rigidity to the bottom rib 30.

The corner L is applied at the bottom in the same manner as at the top of the' tank T. The offset portion 29 is slipped into the lower open end 36 of the side rib 13 and the opposite end of the corner L is placed over the vertical gusset 33 with its outer edge in abutting relation with the bottom rib 30. The corner L is then welded into place with the bottom rib 30 and side rib v 13 along the outer portions 7 and sides 8 thereof and around the curved corner C of the tank T.

In a round corner K (FIG. 3), the neutral axis tends to be closer to the rounded corner C of the tank T so that the-flanges 16 were welded to the tank corner C, and the curved outer portion 18 was made thicker. However, in a square corner L (FIGS. 5-10), the outer portion 7 maintains its stiffness and the neutral axis tends to be farther away from the rounded corner C and toward the apex 24, so no flange such as flange 16 is provided at the corner L. Of course, as the neutral axis is moved outwardly from the tank corner C the strength or stiffness of the corner L is improved. The corners K and L shown in FIGS. 3 and 5 have been tested in special test frames. Calculations and tests indicate that the square corner L is as stiff or as strong as the prior round corner K in this environment (FIG. 3).

As shown herein, one end of the preformed corner L is provided with an offset portion 29 which slips onto the open end of a reinforcing rib R so that a butt weld may be made from one side only and the outer portions 7-and sides 8 of boththe reinforcing rib R and corner L are in edgewise abutting relation. This provides a stronger arrangement than if the corner overlapped the reinforcing rib. The other end of the corner L is welded to a rib R which has either a butt strap 31 or trapezoidal gusset 33 therein. However, the butt strap 31 is provided as a matter of convenience for ease in welding and a butt weld could be used without any back-up such as a butt strap 31 or gusset 33. Of course, the vertical bottom gussets 33 are preferred at points where the bottom rib 30 rests on an I-beam 6. The juncture or weld between the bottom corner L and the bottom rib 30 is positioned directly over the outer longitudinal support beam 6.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is: i 1 I v 1. In a tank made from relatively thin sheet metal, said tank having reinforcing ribs, said ribs being connected to the tank along adjacent walls in registering relation, said tank having a curved corner, said ribs each having an outer portion and two side portions extending therefrom at an angle thereto, said side portions each having a flange thereon parallelto said outer potion and to a tank wall and being connected to said tank wall, said ribs having free end edges which are at right angles to the walls to which said ribs are attached,

the improvement which comprises a corner connecting the ends of registering reinforcing ribs onv adjacent walls of said tank, said corner comprising at least two outer members each having an outer portion and two side portions, said side portions having curved inner edges, each of said outer members having ends angularly positioned to each other at an angle of about 45, the opposing ends of said two outer members positioned at an angle of about to each other, the adjacent ends of said two outer members being connected by means of a central weld positioned at an angle with respect to the outer portion of each of said two members and extending through the apex, said corner having a gusset'plate therein welded within said corner at the 'apex and extending from said apex at-least half the distance from said apex to said tank to strengthen said corner, the ends of said corner and the curved inner edges thereof being welded to the reinforcing ribs and to the curved corner of the tank repsectively, the outer portion and two side portions of said corner being in the same plane as the outer portions and the side portions, respectively, of the ribs to which said corner is welded.

2. The corner set forth in claim 1 wherein each of the outer two members is made from the same material as that used for the tank and the reinforcing ribs.

3. The corner set forth in claim 1 wherein the side portions slope with respect to the outer portion.

4. The corner set forth in claim 3 wherein said central weld is positioned at an angle of about 45 with respect t6 the o iiter portions of said two members and is an in side and outside weld and wherein said gusset plate is welded to the outermost portions of the sloping sides and outer portion of the corner along the apex.

5. The corner set forth in claim 1 wherein the outer portion of each corner segment forms a continuation of the outer portion of a rib on a wall, wherein the sides of the corner segments form a continuation of the sides on said rib on a wall, and wherein the flanges of registering ribs remain unconnected to each other at the corner of the tank.

6. The corner set forth in claim 1 wherein said corner construction is connected to the ends of the registering reinforcing ribs by means of a butt weld at each end of the corner construction.

7. The corner set forth in claim I wherein said corner construction can be fabricated as a unit by welding said two corner segments together along the central weld line at about 45 with an inside and outside weld, said corner construction adapted to be transported as a unit to the location on the tank where it is to be welded thereto.

8. The corner set forth in claim 1 wherein the two side portions are connected to the outer portion of each outer member by means of a fold and not by means of welding.

9. In a tank made from relatively thin sheet metal, said tank having reinforcing ribs, said ribs being welded to the tank along adjacent walls in registering relation, said tank having a curved corner, said ribs each having an outer portion and two sloping side portions extendingtherefrom 'at an angle thereto, said side portions each having a flange thereon parallel to said outer portion and to a tank wall and being welded to said tank wall, said ribs having free end edges which are at right angles to the walls to which said ribs are attached, the improvement which comprises a corner connecting the ends of said registering reinforcing ribs on adjacent walls of said tank, said corner comprising two outer members each folded from a single piece of material to form an outer portion and two sloping integralside portions, said side portions having curved inner flanges, each of said outer members having ends angularly positioned to each other at an angle of about 45, the opposing ends of said two outer members positioned at an angle of about to each other, the adjacent ends of said two outer members being welded together along a central weld at an angle of about 45 with respect to the outer portion of each of said two members and extending through the apex and substantially bisecting the angle between the outer portion of said two members, said corner having a gusset plate therein extending inwardly from said apex at least half the distance along said central weld to said curved tank corner to strengthen said corner, said gusset being welded to corner at the apex and to said side portions of said outer members, one of said two outer members having an inwardly offset portion along one free end thereof adapted to slip into the open end ofa reinforcing rib on a wall of the tank, the ends of said corner and the curved inner edges thereof being welded to the reinforcing ribs and to the curved corner of the tank respectively, the outer portion and two side portions of said corner being in the same plane as the outer portions and the side portions, respectively, of the ribs to which said corner is welded.

Claims

1. In a tank made from relatively thin sheet metal, said tank having reinforcing ribs, said ribs being connected to the tank along adjacent walls in registering relation, said tank having a curved corner, said ribs each having an outer portion and two side portions extending therefrom at an angle thereto, said side portions each having a flange thereon parallel to said outer potion and to a tank wall and being connected to said tank wall, said ribs having free end edges which are at right angles to the walls to which said ribs are attached, the improvement which comprises a corner connecting the ends of registering reinforcing ribs on adjacent walls of said tank, said corner comprising at least two outer members each having an outer portion and two side portions, said side portions having curved inner edges, each of said outer members having ends angularly positioned to each other at an angle of about 45*, the opposing ends of said two outer members positioned at an angle of about 90* to each other, the adjacent ends of said two outer members being connected by means of a central weld positioned at an angle with respect to the outer portion of each of said two members and extending through the apex, said corner having a gusset plate therein welded within said corner at the apex and extending from said apex at least half the distance from said apex to said tank to strengthen said corner, the ends of said corner and the curved inner edges thereof being welded to the reinforcing ribs and to the curved corner of the tank repsectively, the outer portion and two side portions of said corner being in the same plane as the outer portions and the side portions, respectively, of the ribs to which said corner is welded.

4. The corner set forth in claim 3 wherein said central weld is positioned at an angle of about 45* with respect to the outer portions of said two members and is an inside and outside weld and wherein said gusset plate is welded to the outermost portions of the sloping sides and outer portion of the corner along the apex.

7. The corner set forth in claim 1 wherein said corner construction can be fabricated as a unit by welding said two corner segments together along the central weld line at about 45* with an inside and outside weld, said corner construction adapted to be transported as a unit to the location on the tank where it is to be welded thereto.

9. In a tank made from relatively thin sheet metal, said tank having reinforcing ribs, said ribs being welded to the tank along adjacent walls in registering relation, said tank having a curved corner, said ribs each having an outer portion and two sloping side portions extending therefrom at an angle thereto, said side portions each having a flange thereon parallel to said outer portion and to a tank wall and being welded to said tank wall, said ribs having free end edges which are at right angles to the walls to which said ribs are attached, the improvement which comprises a corner connecting the ends of said registering reinforcing ribs on adjacent walls of said tank, said corner comprising two outer members each folded from a single piece of material to form an outer portion and two sloping integral side portions, said side portions having curved inner flanges, each of said outer members having ends angularly positioned to each other at an angle of about 45*, the opposing ends of said two outer members positioned at an angle of about 90* to each other, the adjacent ends of said two outer members being welded together along a central weld at an angle of about 45* with respect to the outer portion of each of said two members and extending through the apex and substantially bisecting the angle between the outer portion of said two members, said corner having a gusset plate therein extending inwardly from said apex at least half the distance along said central weld to said curved tank corner to strengthen said corner, said gusset being welded to corner at the apex and to said side portions of said outer members, one of said two outer members having an inwardly offset portion along one free end thereof adapted to slip into the open end of a reinforcing rib on a wall of the tank, the ends of said corner and the curved inner edges thereof being welded to the reinforcing ribs and to the curved corner of the tank respectively, the outer portion and two side portions of said corner being in the same plane as the outer portions and the side portions, respectively, of the ribs to which said corner is welded.