US2944693A

US2944693A - Expansible container for fluids at low temperature

Info

Publication number: US2944693A
Application number: US726112A
Authority: US
Inventors: Walter L Benson; Norman C Dahl
Original assignee: Constock Liquid Methane Corp
Current assignee: Constock Liquid Methane Corp
Priority date: 1958-04-03
Filing date: 1958-04-03
Publication date: 1960-07-12
Anticipated expiration: 1977-07-12

Description

EXPANSIBLE CONTAINER FOR FLUIDS AT LOW TEMPERATURE Filed April 5. 1958 IN VEN TORS Walfer L. Benson by Norman C. Dahl am, mdvyal, 77M I M AT TORNEYJ' United States Patent This invention relates tostoring and shipping liquefied a 2,944,693 Patented July 12., ieeo ing to enable deformation ,whichrwould rallow rthe walls .gases at low temperatures and more particularlyto the 1 storing and handling of such liquefied gases in large atrleltal :tanks which are surrounded by insulating Illa-t6- vma s.

Many types of containers suitable for handling liquids which 'must be maintained at relativel-y low temperatures are known and used. One of the most common of these .is themetal tank set-completely within another tank or receptacle with insulation material placed in the space between the inside metal tank and-the outsiderece'ptade.

Because the inside tank is metalit possessesacoeflicientof therma-l expansion and hence is subject; to 1 contraction and expansion when "exposed ?to temperature changes. ,The :problem of expansion and contraction becomes markedlyvacute at the temperatures -.nor.mally .eneoun- ,tered-in the handling of liquefied gases because the vvtemperature differential between the liquefied gas temperature and normal'room temperature is very great."

- .In the case where-the inside tank designed for storing or shipping liquefied gases is completely surrounded by an insulating material, such as balsaor cellular glass for example, contraction-of the ftankjwalls when :the

liquefied gas is added means that'the wall-sspull away 7 pressure of the liquid load Within-the inner'tankainraddit'ion to the pressure under which the'liquid and vapor, -.f1lling the space above theliquid, might be maintained within the tank. ,Repetition of the -cooling-warrning 'cycle, 1 brought about by the addition andwemoval of .ithe liquefied gas, and hence-{of the streSSes Setu 'afte'rta relatively short .period, may causethe. inner" tank to fail. 1 v 1 Moreover; if; 'thejinner 'tarik 'cont-ainingithe liquefied 'i'gas is onlygpartially,filled-2a large temperature gradient will exist in the gas column above the aliquiddeve'l.

means that thetank walls will' also exhibit ama'rkedtemperature gradient approximating the itemperature'igradient in-the :gasbecause oftthe'averylowztherrnalconductivity of metal walls at the low temperatures: involved.

The resulting temperature tgraulients' introduce additional stresses in "the-walls whichzr'nay 'beipa'rtiallytreiieyedwby the tank desi'gn of thisinvention. I

it would 'be. desirable to be ablei-to Yfiabricatecme'tal :tar'iks for the storage of a :eold boilingliquid inll-arge cprnenp rtip offtheitank;continuously to engage the winsulation layer for support. v Z1]; rigitherefore, an object of this invention toiprovid'e a tank, suitable v for' storing and shipping liquefied gases,

hich 'mayibe constructedofsthin metal walls, thusresultingt-inlower constructioncosts.

It is an additional objectto provide receptacles, rsuitableiorzstoring and shipping liquefied gases, which remain continuously in contact with insulating material surrounding them;

11 is another object to provide receptacles, suitable for storing and shipping liquefied gases, which remain "continuously incontact with insulating material surrounding themand which employ'an insulation in .comhinationtherewith characterized by having ;a structural strengthsufiicient to maintain their mass integrity and shape under load to provide an adequate support for the innermetal tank. 7 i

It'is another objectdoprovide an inner receptacle for storing and shipping liquefied gases which depends for -a3p0rtion-of its structuralvsupport upon an outside receptaele, his a further object of this invention to provide receptacles, suitable for storing and shipping liquefied gases, which are expansible under the hydrostatic load vand under the ,pressure built up Within .the receptacle by the vaporizationof the liquid into gas. These and other objects, will appear in the following discussion which ris gpresented with reference to the accompanying drawing which- .F i,g. :1 represents a cross-sectional View of the type of tank construction to which this invention is applicable; 2 .is a perspective view of three walls of a tank Joined at-atcorneriin accordance with this invention;

' Eig. 3 lis gplan view of a .cornerof a tank having all three wallsmeeting atthe cornerjoined by the cylindrical "eXpansion-joints-of this-invention;

-4 is afront elevation-of th'e cornerof Fig. 3, and

Fig. 5 is a cross-sectional view of section 5-5 of vgut- 3. 7. By -.theqpr'oeess of this invention, a tank suitable for ithe storage :andiran-sportation of liquefied gases is :rnade expansibleto-allow-the sides of the tank to rernainsubstantially v continuously in contact with the insulation and vhence to make ,full use-of the additional structural suppor,t'offered by the insulation alone or in combination :withthe outside receptacle. This is done, in'accordance iwi-th the practice of ;this invention, by connecting the ,gwa lls-of the (tank byimeans-of cylindrical expansion joints.

111 the-tank: of thisjzinvention, a single expansion joint is $11-23}; ;th e;edge of each gplane of the-tank to form-the art 5 byitn I dflfbrmation of th iQint-s to relieve the stresses onithe tank-walls ian tov enableideformation suificientrto enable the tank wallsdofremain substantially in surface contact -;With 1:11.3 tinsulationdayer notwithstanding the expansions aorseontractions iwhich :take-place in the metal during changes .in the temperature thereof. pinyention may be better described in detail with reference totthe ifigures Ibis preferred to make use of an expan- 0 esion joint ofzcylind'riealeor curvilinear shape, :as-shown, "but wolume'l wherein the -tanks'eoiildibetfabricatd of aniinner.

riit-willrbe understood-that: expansion jointsiofothenshapes mndscrossesection gmay be':'emp1oyed. When zexpansion between the walls, The internabpressure @liquidand' by the :liquefiedgas will cause 7 The tanks of this joints of such other configuration are employed, it is desirable to avoid the use of sharp corners in the connecting planes since it will be apparent that flexure for expansion and contraction of the tank will occur manytimes in.use.

In Fig. 1 there is shown a simplified cross-sectional drawing of the general type of tank used for storing or shipping liquefied gases. The tank will be a polyhedron configuration and preferably one which'is a rectangular parallelepiped. Inner tank 10, designed to contain the liquefied gas 13, is placed within a surrounding vessel 11 and insulating material 12 placed between them. Such a tank may be equipped with a filling line 21 in which is placed a pressure-regulating valve 20 to provide-proper gas venting, and with a draw-off line 22 incorporating valve 23. When the sides, top and bottom of tank press closely on the insulating material, tank 10 forms an integral unit with tank 11 and tank 10 may therefore be of a lighter weight, thinner construction than if this integration did not exist. When the walls of tank 10 are cooled by the introduction of the liquefied gas, they contract, if made in the conventional manner, and pull away from the insulation and destroy the necessary integration and interaction.

In a tank such as shown in Fig. 1, the surrounding vessel 11 may be eliminated where insulation 12 is of such structural material, such as cellular glass, cork or balsa wood, that it forms a strong outside receptacle. In such a case, by maintaining the tank walls 10 in contact with insulating material 12 a strong integral unit is achieved Without the additional tank 11.

The manner in which the walls of the tank of this invention are made expansible is shown in Fig. 2- which illustrates how three walls 16 are joined at a corner. Three-quarter cylindrical sections 18 are welded along wall edges 19 and at their lines of intersection 17. Figs.

3 and 4 (in which like numbers refer to like elements of Fig. 2) are a plan view and a front elevation view of the corner of Fig. 2 in which three walls are joined by the expansible cylindrical joints of this invention.

In Fig. 5, two expansible walls 16 across section 5-5 of Fig. 3, are shown joined by a three-quarter cylindrical expansion joint 18 at their points of contact 19. Pres-- sure, applied in the direction of the arrows, causes the expansion joint to become deformed, thus giving suflicient spring or expansion to walls 16. Likewise, when walls 16 are brought into contact with the liquefied gas at low temperature they will contract again causing the cylindrical expansion joints to deform, thus relieving the stresses of'contraction in walls 16.

Although it will generally be convenient to have all of the sides, along with the top and bottom, joined by means of the cylindrical expansion joints, there may be tank designs in which less than all of the surfaces making up 'the tank walls will require cylindrical expansion joints.

Thus, for example, if a tank were constructed so that its height/cross-sectional dimension ratio was very high, the top and bottom could be rigidly attached to the sides which in turn would be joined by the cylindrical expansion joints. Likewise, if it is possible to allow'the tank to slide freely within the enclosure formed by the insulation, it would be feasible to join only two'adjacent walls and the top of the tank by means of the cylindrical expansion joints. The remaining walls-may then be-joined by any suitable method. Thus, a number of combinations are possible, the final design considerations governing the choice made from these combinations.

The walls and cylindrical expansion joints of the tanks of this invention may conveniently be constructed of stainless steel. However, other suitable metals, such as aluminum and copper or alloys, which possess the desired structural strength and degree of resilience, maybe used.

When use is made of the tank for the storage or transportationof a very low boiling liquefied gas, such as in .the storage or transportation of liquefied natural gas .edges of the sides of said polyhedron .or curvature is the thickness of the material of which the expansion joint is formed'and the pressure at which the tank operates. As an example, the radii may vary from 4.8 inches to 8.7 inches for stainless steel cylinders made of 0.037 inch to 0.125 inch material when the tank has an internal pressure of about 20 p.s.i.g. Generally, for a given stress and deflection, the thicker the cylinder material, the greater the radius must be. Other design factors which must be considered in determining material thickness and cylinder radius are the material used for tank construction, the degree of flexibility required, the internal pressure of the tank, overall dimensions of the tank, and the number of walls or surfaces joined in the manner of this invention. All of these factors must be balanced in the design of a tank for a particular purpose.

The cylindrical expansion joints may conveniently be die pressed, but any suitable method of forming may also be used. Although welding is usually the preferable manner of joining the walls to the cylindrical expansion joints, other suitable methods such as crimping may be used. The final tank will be so constructed as to atford a hermetically sealed container suitable for holding liquefied gas.

Thus, by the use of the expansible tanks of this invention, there are provided means for continuously keeping the outside of the tank walls in contact with the insulating material surrounding the tank which in turn means that thin-walled tanks may be used since the tank can be structurally supported by the insulation and the outside'tank or by the insulation alone.

"We claimi '1. In a tank for the storage of a liquid, the boiling point of which difiers widely from the ambient tempenature, comprising an inner shell housing said liquid and which is subject to noticeable expansion and contraction due to temperature change, an outer shell spaced from the inner shell to provide a confined space therebetween, and thermal insulating material between the shells, the improvement wherein said inner shell having the shape of a polyhedron is provided with an expansion joint at each of the sides of said polyhedron, each such expansion joint being in the form of a curvilinear section extending continuously throughout the lengths of the joined sides, the outer surface of said section being convex with respect to the interior of the inner shell, and the two edges of said section being hermetically sealed to the adjacent edges of the two sides which it joins, whereby the inner shell remains continuously in contact with the insulating material. Y 2. A tank according to claim 1 wherein said inne shell is a rectangular parallelepiped. 5

.3. A tank according to claim '1 wherein all of a the are provided with said expansion joint.

4. A tank according to claim 1 wherein said expansion joint is in the form of a major part of a. cylinder having its axis parallel to the contiguous edges of the sides which it joins.

5. A tank according to claim 4 wherein said expansion joint is in the form of a three-quartered cylinder.

6. In a tank of large capacity for the storage of a liquefied natural gas at about atmospheric pressure comprising an inner shell formed of a metal capable of retaining its ductility at the low temperature of the lique- V to expansion and'contraction in response to temperature change an outer shell'surroundingthe inner shell in I spaced relation therewith to provide an open space in between filled with thermal insulation materiaL'the im-' provement wherein said inner shell having the shape of a polyhedron is carried outwith thinmetal walls provided with an expansion joint at'each of a plurality of the edges of the walls of said polyhedron, each such expansion joint being in the form of a curvilinear section extending continuously throughout the lengths of the joined walls, the outer surface of said section being convex with respectto thie interior of the inner shell, and the two edges of said section being hermetically sealed to the adjacent edges of the two walls whichit joins and from which said edges of the two walls extend tangentially, whereby the inner shell remains continuously in contact with the insulation material and depends upon the outer shell or'the insulation material layer for structural support.

References Cited in the file of this patent UNITED STATES PATENTS 71,222 Rohrman Nov. 19, 1867 474,563 Moore May 10, 189 2 FOREIGN PATENTS 64,927 Germany Dec. 19. 1891