TANK SHELL FOR AN OUTER LNG CONTAINMENT TANK AND METHOD FOR MAKING THE SAME
A shell for an outer LNG containment tank and a method of making the shell from a plurality of precast reinforced concrete shell elements are described. The shell elements having a precast concrete body to which are anchored a radially inwardly facing liner plate and a pair of circumferentially spaced apart side plates which depend radially outwardly from the liner plate. The shell elements can be arranged upon a ring beam with side plates abutting one another. The side plates are welded together to form radially and vertically extending stiffener ribs which are circumferentially spaced around the shell. As these stiffener ribs provide great structural support, the shell can be constructed with minimal or no cast in place structural joints being needed to construct the shell. Ideally, the shell elements have bottom base plates welded to a ring beam or foundation and top end plates that are welded together to form an annular ring thus enhancing the structural strength of the shell. A roof can be mounted to the shell to create an outer LNG containment tank.
Latest Patents:
The present invention relates generally to the construction of LNG (liquefied natural gas) storage tanks, and more particularly, to methods for constructing shells or tank walls for very large structures.
BACKGROUNDLarge storage tanks are typically designed with a so-called “shell”—a reinforced concrete circular wall centered continuously on top of and integrally connected to the tank foundation. Shell walls may be large structures and are often cast in place on top of a ring beam foundation. With very large tanks, this casting in place construction is a time-consuming process and may be problematic at remote site locations. Building with precast concrete elements is a known approach in the construction of various structures when construction time at the site needs to be minimized, and when site conditions and location are problematic for casting in place. However, shells are very specific structural elements due to their function and configuration in large storage tanks and are not easily constructed. Effective connections between the separate precast segments are difficult and time consuming to construct. Cast in place connections between shell elements have been one conventional manner for joining such shell elements.
The walls of large storage tanks need to be reinforced to handle construction, operating and earthquake loads. Conventional construction of the shell is to erect the inner metal liner first then erect rebar and forms followed by slip forming the concrete. To use precast concrete shell elements, the elements are spaced a short distance apart to allow rebar connections (either mechanical or welded) followed by slip form casting of the gaps between the elements. Then the gap is covered with steel and the concrete is cured for a short time, i.e., about 3-5 days. The total shell erection time is dependent on these connection curing times to complete the shell circumference so that additional construction load may be safely applied to erect the roof.
An example of a full containment LNG tank design is defined in European codes such as British Standard 7777. An outer secondary container or tank acts as a catch basin in case of a leak or tank rupture of an inner container, which is often a steel tank. Also, the outer tank is made of concrete which reduces the fire risk over that of steel. However, the outer tank shell is either slip formed in place and post tensioned or a steel liner is used as a form and rebar added after the steel liner is erected, then slip or jump formed. Either method can be quite time consuming.
SUMMARYA shell for an outer LNG containment tank and a method of making the shell from a plurality of precast reinforced concrete shell elements are described. The method comprises providing a plurality of precast reinforced concrete shell elements. At least some of the shell elements having a precast concrete body to which are anchored a radially inwardly facing liner plate and a pair of radially extending and circumferentially spaced apart side plates which depend from the liner plate. The shell elements are juxtaposed upon a ring beam with side plates abutting one another. The abutting side plates are welded together to at least partially form the shell. The cooperating welded together side plates form radially extending stiffening ribs which are circumferentially spaced around the periphery of the shell.
Ideally at least some of the shell elements include a base plate and a top end cap plate. The base plates are welded to the ring beam and the top end cap plates are welded to one another to form an annular ring of top end cap plates. Preferably, the liner plates and side plates cooperate to form a continuous inner radial membrane to the shell. In one embodiment, at least some of the shell elements have mechanically interlocking surfaces and at least some of the shell elements interlock with one another before being welded together. The shell may be made from a single course of shell elements or from a number of circumferentially extending and vertically arranged courses of shell elements.
A shell for an outer LNG containment tank is also described. The shell comprises a plurality of precast reinforced concrete shell elements, at least some of the shell elements having a precast concrete body to which are anchored a radially inwardly facing liner plate and a pair of radially extending and circumferentially spaced apart side plates which depend from the liner plate. At least some of the shell elements are arranged circumferentially with abutting side plates being welded together to at least partially form a shell and to form radially extending stiffening ribs which are circumferentially spaced about the periphery of the shell. Preferably, at least some of the shell elements further include bottom base plates which are welded to a ring beam to provide additional support to the shell. Further, at least some of the shell elements can have top end cap plates which are welded to one another to form a circumferential extending annular ring of end cap plates. Ideally, the liner plates and side plates cooperate to form a continuous inner radial membrane to the shell. Also, in one embodiment, at least some of the shell elements have mechanically interlocking surfaces and the at least some of the shell elements interlock with one another. The interlocking surfaces can include cooperating projections and receptacles. The shell can include one or multiple courses of circumferentially extending and vertically arranged courses of shell elements which are welded together to form at least a portion of the shell.
The shell can have a shell access opening formed therein. The shell access opening can be sealed by at least one cast in place shell element having a liner plate which cooperates with the liner plates and sides plates of the precast shell elements to seal the access opening. Another alternative is to seal the shell access opening with at least one precast shell element having a liner plate, the at least one precast shell element cooperating with other liner plates and sides plates of the shell to seal the access opening.
A shell element for constructing the shell of an outer LNG containment tank is also disclosed. The element comprises a precast reinforced concrete body to which are anchored a radially inwardly facing liner plate and a periphery formed by a pair of vertically extending circumferentially spaced apart side plates, a bottom base plate and a top end cap plate. A plurality of the shell elements may be arranged in circumferential abutment and the side plates welded together to form radially extending stiffener ribs and the liner plates form part of radial inwardly facing shell membrane.
It is an object to provide precast concrete shell elements that have steel liner plates that can be quickly fit together and the shell elements welded to form a shell circumference.
These and other objects, features and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where:
In a first embodiment, a full containment LNG tank 18 is shown in
In this particular embodiment, outer tank 20 is primarily made of precast reinforced concrete elements which reduce fire risk relative to using a primarily steel outer container or tank. The construction of outer tank 20 involves assembling precast reinforced concrete elements for a foundation 24, including a base mat assembly 100 and an outer ring beam 200, an outer wall or shell 300 and a roof 400. As an example of order of magnitude, outer tank 20 in this embodiment has a diameter of approximately 80 meters, an overall height (to the top of the dome of roof 400) of about 50 meters, and a height to the top of shell 300 of about 40 meters. Those skilled in the art of LNG facilities construction will appreciate that much larger or smaller tanks can be built and still use the design considerations described herein. However, tanks having diameters of at least 25 meters are particularly well suited to the construction methods described herein which utilize precast reinforced concrete elements. These elements ideally can be welded together to form structural welds thereby minimizing the number of cast in place concrete structural joints which have to be made to form an outer containment tank.
Ideally, inner tank 22 can be assembled at the same time as roof 400 is being built to save time and money in the overall construction of inner tank 22 and outer tank 20. Note in
Inner tank 22 can be built in any of a number of ways which may require welding processes to connect individual plates. For example, the plates can be joined using shielded metal arc welding (SMAW) and submerged arc welding (SAW) for 9% nickel tanks of the size described above, i.e. having a diameter greater than 25 meters. In this particular example, inner tank 22 can be friction stir welded (FSW) by plate at a time erection method. A course of plates at a time can be welded with the bottom (thickest) first and then subsequent (thinner) courses welded there above. Scaffolding (not shown) can be used as each course is added. Alternatively, inner tank 22 can be constructed course down either by supporting the tank from the roof to allow insertion of the next course or by supporting on jack stands to allow insertion of the next course. For the last two methods, the scaffolding need be erected only one time. By way of example and not limitation, another alternative method is to use coil material shaped to the curvature required for the tank. Coil tank building occurs from the top course down either using jacking or by roof supported. Expanded pearlite insulation is typically used in the annulus formed between inner tank 22 and outer tank 22. Although not shown, an under bottom insulating layer, which can be made of foam glass, is applied on the top of base mat assembly 100 with inner tank 22 prior to inner tank 22 being placed there on.
Foundation 24, i.e., base mat assembly 100 and ring beam 200, is designed to support inner tank 22 and outer shell 300. Outer shell 300 rests upon and transfers loads directly to outer ring beam 200 preferably through welded connections. A particularly significant load is the torsional load applied to ring beam 200 from outer shell 300. Base mat assembly 100 is secured to and transfers loads to outer ring beam 200 as well through a cast in place joint 270, which is best seen in
Concrete ribs 130 and grooves 132 are also formed on the longitudinally and laterally extending edge surfaces of concrete body 114. Locating projections 106 and ribs 130 and receiving recesses 110 and grooves 132 allow a plurality of base mat elements 102 to be placed in interlocking juxtaposition as suggested in
The rows of tensile conduits are disposed below and above the central horizontal plane 144 of concrete body 114. These laterally and longitudinally extending tensile conduits are designed to receive tensile members 150 there through which allow multiple base mat elements 102 to be clamped together utilizing anchors 152 (
Base mat assembly 100 is constructed by juxtaposing base mat elements 102 in both first and second generally perpendicular directions as seen in
Tensile members 150 are fed through tensile conduits 120, 122, 124 and 126 as base mat elements 102 are being juxtaposed to one another. After the mating surfaces on the base mat elements 102 are properly located relatively to one another, tensile members 150, i.e. cables, are post-tensioned and anchored by anchors 152 to clamp base mat elements 102 together. In this particular example, tensioning can be accomplished such as by using a Williams Strand Anchor System available from Williams Form Engineering of Belmont, Mich., USA. Those skilled in the art will appreciate that other tensioning systems can also be used to post-tension and anchor tensile members 150. After the tensioning is complete, anchors 152 are locked in place on tensile members 150 to maintain the tension in tensile members 150 with anchors 152 bearing upon base mat elements 102.
Liner plates 104 of each of base mat elements 102 are then welded together to form a part of a generally contiguous membrane 140 on the top of base mat assembly 100. As tensile conduits 120, 122, 124 and 126 are located above and below the central horizontal plane 144 of concrete body 114, the top and bottom surfaces of base mat elements 102 are held together and do not separate due to the post tensioning of tensile members 150 with anchors 152 clamping about base mat elements 102, preferably even under construction and operating loads applied to base mat assembly 100.
C. Mounting of Base Mat Elements on PilesBase mat elements 102 can be assembled on a graded, level surface if the underlying surface or soil is sufficiently stiff. However, if the soil does not provide adequate support, base mat elements 102 can be mounted on piles 160. The upper portion of a typical pile 160 is seen in
The corners and long sides of base mat elements 102 will be supported by six cooperating supporting flanges 166. Voids 174 are created by the intersection of the corners and along the sides of cooperating base mat elements 102. In the case where piles are used, base mat elements 102 can include reinforcing bar loops (not shown) which are embedded in concrete body 114 and extend laterally and longitudinally from concrete body 114. The loops will loop over vertically extending reinforcing bars 170. Concrete is cast in these voids 174 about the loops and reinforcing bars 170. Fitted liner plate 176 is anchored by J-hooks in the cast concrete so that liner plates 104 and 176 can be welded together to form generally continuous top membrane 140 on base mat assembly 100.
III. Outer Ring Beam 200Also formed within concrete body 220 are circumferentially extending lower and upper tensile conduits 232, 234. In this particular embodiment, there are four such tensile conduits 232, 234. Two of these tensile conduits 232 are generally arranged below and two conduits 234 are arranged above the horizontal center plane 236 of ring beam element 202. Also, two of the tension conduits 232, 234 are arranged beneath base plate 206 and two are located radially inwardly beneath liner plate 204 closer to the inner radial surface 224. These cooperating locations of tensile conduits 232, 234 allow tensioning members 250, i.e., cables, to pass through each of ring beam elements 202 and assist in counter balancing the bending, shearing and torsional loads applied to base plate 206 by outer shell 300. Also, tensile members 250 and anchors 252 cooperate to clamp about ring beam elements 202 to prevent the abutting ring beam elements 202 from displacing with respect to one another. In this particular example, high density polyethylene (HDPE) tubing is used to form the tensile conduits 232, 234 in concrete body 220. Of course, the tensile conduits could be made of other suitable materials such as steel or other structurally strong materials. Downwardly and upwardly opening steps 238 and 240 allow elements 202 to be vertically interlocking as well. Also, located within concrete body 220 is a plurality of reinforcing bars (not shown) which are conventional for adding tensile strength to cast concrete bodies. Extending radially inwardly are reinforcing bars or J-hooks 242 which are later to be included in cast concrete connection 270 which connects base mat assembly 100 with ring beam 200.
Ring beam elements 202 are juxtaposed with respect to one another with locating concrete ribs 226 of one ring beam element being held within locating recess 230 of the adjacent ring beam element. Similarly, cooperating steps 238 and 240 assist in vertical alignment between ring beam elements 202. Tensile members 250 are placed through tensile conduits 232 and 234 as the ring beam elements are being positioned adjacent one another. As seen in
After the individual ring beam elements 202 are aligned and clamped together using tensile members 250 and anchors 252, base plates 206 are welded together along their radially extending abutting edges to form an annular ring which strengthens outer ring beam 200. Finally, liner plates 204 on ring beam elements 202 are also welded together along their radially extending edges to form a continuous membrane 244 on the radial inner side of outer ring beam 200, as best seen in
Each of shell elements 302 includes a pair of tapered carbon steel side plates 304 and a carbon steel liner plate 306 forming a generally U-shaped steel cross-section. In this example, the liner plate 306 is about 10 mm thick and side plates 304 are about 25 mm thick. The width of side plates 304 is about 800 mm at their bottom and 400 mm at the top providing the tapered shape to shell element 302. A base plate 312 connects side plates 304 and liner plate 306 at the bottom of shell element 302. Numerous reinforcing bars 310 are welded to and extend from side plate 304 to the opposing side plate 304 and from base plate 312 to top end cap 314. Base plate 312 is about 50 mm in thickness in this example. A steel end cap plate 314, also about 50 mm thick, is welded to side plates 304 and steel liner plate 306 at the top of shell element 302. Concrete is cast in place in the U-shaped volume defined by side plates 304 and steel liner plate 306 and about reinforcing bars 310 and J-hooks 316 to form reinforced concrete body 318. Liner plate 306 acts as a vapor/gas barrier
B. Constructing Shell 300Shell 300 is constructed by arranging shell elements 302 vertically upon outer ring beam 200. Initially, base plates 312 are arranged radially slightly outside of their final position for welding with shell elements 312 being slightly radially spaced apart. Shell elements 302 are then moved radially inwardly until all base plates 312 and side plates 304 are brought into abutment at the proper radial position atop of base plates 206 of ring beam 202. Erection gear will be used to finally align and pull the side plates 304 closely together to begin welding.
As seen in
All of shell elements 302 are permanently welded together to form shell 300, with the exception of 2-4 special half shell elements 302′. Half shell elements 302′ are similar to shell elements 302 except they are only about half the height of regular shell elements 302. These special shell elements 302′ will be temporarily sealed with shell opening 350 to accommodate air raising of roof assembly 404, as suggested in
As an alternative to permanently closing construction opening 350, liner plates can be welded to close shell opening 350. Then reinforcing bars and steel rib stiffeners can be placed in a form and concrete can be cast in place to form a cast in place shell element similar to that used in the design of the precast shell elements 302. Shell 300 should have great strength when completed due to the welded connections 320 on the inner and outer edges of side plates 304 which cooperate to form a large number of radially extending stiffeners arranged around the circumferential periphery of outer tank 20.
C. Alternate Shell DesignUpper shell element 302b includes a concrete body 316b to which a pair of circumferentially spaced apart side plates 304b, liner plate 320b, upper end cap plate 314b and lower base plate 312b are anchored (anchors and reinforcement bars not shown). Two downwardly depending and circumferentially spaced apart alignment pipes 360 are welded to lower base plate 312b. As seen in
Referring in general now to
Once enough weld joints have been formed to safely support roof 400, the pressurization within shell 300 is removed. Personnel can then access the inside of the outer tank 20 to construct inner tank 22. Additional welding is done to complete the circumferential weld joint between the roof membrane 412 and shell membrane 340. Special extra strength roof elements 402′ are attached to shell 300 and roof frame 404 forming the radial outermost course of roof elements 402. Then typical roof elements 402 are attached to roof frame 404 with the radial outermost course of roof elements 402 being attached first. Then the successive next radial outermost course of roof elements is added until all the rings of roof elements 402 are in place forming roof 400.
A. Roof Assembly 404Roof assembly 404 is built on the ground in this particular preferred exemplary embodiment. Roof frame 406 comprises a plurality of radially and circumferentially extending wide flange beams 420, as best seen in
Referring now to
Half shell elements 302′ are removed to provide access from within shell 300. Referring now to
Roof elements 402 and 402′ are mounted to roof assembly 404 after roof assembly 404 has been affixed by weldments to shell 300.
Reinforcing bars 436 extend laterally and longitudinally between opposing brackets 432. Roof element frame 428 is used to construct precast reinforced concrete roof elements 402, as seen in
For the outermost concentric course of roof elements 402′ which secure to both roof assembly 404 and to shell 300, the design is slightly different from that of roof elements 402 disposed on the inner radial concentric courses. As shown in
The outer concentric ring or course of roof elements 402′ are located adjacent shell 300 and this outer ring of roof elements 402′ is first welded to roof assembly 404 and to shell 300. This outer ring of roof elements 402′ adds significant strength to roof 400. Subsequently, second through eighth courses of roof elements 402 are sequentially welded to roof assembly 404 starting from the radially outermost course and then each concentric course of roof elements is added until all rows of roof elements 402 are in place to form a complete roof 400 such as seen in
L-shaped brackets 432 of roof elements 402 are mounted atop and are welded to tubular mounting beams 414 creating welds such as the weld joint 436 seen in
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to alteration and that certain other details described herein can vary considerably without departing from the basic principles of the invention. For example, any one or more of base mat assembly 100, ring beam 200, outer shell 300 or roof 400 could be constructed using conventional cast in place construction techniques while the other components are constructed using the precast elements as described herein. As another example of an alternative embodiment, the roof assembly could be directly built atop shell 300 such as by using a crane. In this instance, roof assembly 404 would not have to be airlifted and attached atop shell 300. However, ideally even in this embodiment, the shell elements 402 could be welded to the roof assembly concurrently with the construction of the inner tank 22 to save construction time on building outer tank 20 and inner tank 22.
While beam ring 200 described in the above particular exemplary embodiment was used in conjunction with a full containment LNG tank, a beam ring could certainly be used in other applications. For example, the ring beam could be used in cases where neither a liner plate or thick structural base plate is necessary. In this case, the ring beam need only comprise ring beam elements having precast reinforced concrete bodies with embedded tensile conduits which receive tensile members there through so that the tensile members may be tensioned and anchored by anchors to form the beam ring. Although not required, preferably the ring beam elements would be interlocking with one another.
Claims
1. A method for constructing a shell for an outer LNG containment tank, the method comprising:
- providing a plurality of precast reinforced concrete shell elements, at least some of the shell elements having a precast concrete body to which are anchored a radially inwardly facing liner plate and a pair of radially extending and circumferentially spaced apart side plates which depend from the liner plate;
- juxtaposing the shell elements upon a ring beam with side plates abutting one another; and welding abutting side plates together to at least partially form the shell and to form radially extending stiffening ribs which are circumferentially spaced around the periphery of the shell.
2. The method of claim 1 wherein:
- at least some of the shell elements include a base plate and a top end cap plate;
- and the base plates are welded to the ring beam and the top end cap plates are welded to one another to form an annular ring of top end cap plates.
3. The method of claim 1 wherein:
- the liner plates and side plates cooperate to form a continuous inner radial membrane to the shell.
4. The method of claim 1 wherein:
- at least some of the shell elements have mechanically interlocking surfaces and the at some of the shell elements interlock with one another before being welded together.
5. The method of claim 4 wherein:
- at least some of the interlocking surfaces include cooperating projections and receptacles.
6. The method of claim 1 wherein:
- the shell includes at least two circumferentially extending and vertically arranged courses of shell elements which are welded together to form at least a portion of the shell.
7. The method of claim 1 further comprising:
- constructing the shell to include a shell access opening therein to allow access within the shell.
8. The method of claim 7 further comprising:
- sealing the shell access opening with at least one temporary liner plate; pressurizing the inside of the shell to air lift a roof assembly to the top of the shell;
- mounting the roof assembly to the shell;
- unsealing the shell access opening to access the interior of the shell to construct an inner tank while roof elements are welded to the roof assembly to form a roof atop the shell;
- and permanently sealing the shell access opening after the inner tank is constructed.
9. The method of claim 7 further comprising: casting in place a concrete body which anchors to the at least one temporary liner plate to effect the permanent sealing of the shell access opening.
10. The method of claim 7 further comprising:
- permanently sealing the access opening utilizing at least one temporary liner plate, the temporary liner plate being part of a precast reinforced concrete shell element.
11. A shell for an outer LNG containment tank, the shell comprising:
- a plurality of precast reinforced concrete shell elements, at least some of the shell elements having a precast concrete body to which are anchored a radially inwardly facing liner plate and a pair of radially extending and circumferentially spaced apart side plates which depend from the liner plate;
- wherein the at least some of the shell elements are arranged circumferentially with abutting side plates being welded together to at least partially form a shell and to form radially extending stiffening ribs which are circumferentially spaced about the periphery of the shell.
12. The shell of claim 11 wherein:
- at least some of the shell elements further include bottom base plates which are welded to a ring beam to provide support to the shell.
13. The shell of claim 11 wherein:
- at least some of the shell elements further include top end cap plates which are welded to one another to form an annular ring of end cap plates.
14. The shell of claim 11 wherein:
- the liner plates and side plates cooperate to form a continuous inner radial membrane to the shell.
15. The shell of claim 11 wherein:
- at least some of the shell elements have mechanically interlocking surfaces and the at least some of the shell elements interlock with one another.
16. The shell of claim 15 wherein:
- at least some of the interlocking surfaces include cooperating projections and receptacles.
17. The shell of claim 11 wherein:
- the shell includes at least two circumferentially extending and vertically arranged courses of shell elements which are welded together to form at least a portion of the shell.
18. The shell of claim 11 wherein:
- the shell has an shell access opening formed therein; and the shell access opening is sealed by at least one cast in place shell element having a liner plate which cooperates with the liner plates and sides plates of the precast shell elements to seal the access opening.
19. The shell of claim 11 wherein:
- the shell has an shell access opening formed therein; and the shell opening is sealed by at least one precast shell element having a liner plate, the at least one precast shell element cooperating with other liner plates and sides plates of the shell to seal the access opening.
20. A shell element for constructing the shell of an outer LNG containment tank, the shell element comprising:
- a precast reinforced concrete body to which are anchored a radially inwardly facing liner plate and a periphery formed by a pair of vertically extending circumferentially spaced apart side plates, a bottom base plate and a top end cap plate;
- wherein a plurality of the shell elements may be arranged in circumferential abutment and the side plates welded together to form radially extending stiffener ribs and the liner plates form part of radial inwardly facing shell membrane.
Type: Application
Filed: Dec 23, 2008
Publication Date: Jun 24, 2010
Applicant:
Inventors: Lestle R. Shockley (San Ramon, CA), Vincent G. Borov (Martinez, CA)
Application Number: 12/342,486
International Classification: E04B 7/10 (20060101); E04B 7/00 (20060101);