US3425584A - Shipboard mounting liquefied gas tanks - Google Patents

Description

Feb. 4, 1969 w. F. KIRKPATRICK 3,425,534

SHIPBOARD MOUNTING LIQUEFIED GAS TANKS Filed Oct. 19. 1966 FIGI SHIP LONGITUDINAL BULKHEAD SIDEWALL OF LPG TANK FIGZB INVENTOR WILLIAM F. KIRKPATRICK ATTORNEYS United States Patent O 3,425,584 SHIPBOARD MOUNTING LIQUEFIED GAS TANKS William F. Kirkpatrick, Tokyo, Japan, assignor to California Texas Oil Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 19, 1966, Ser. No. 587,801 U.S. Cl. 220-15 Int. Cl. B65d 25/24; B63b 25/14, 25/16 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a means for supporting independent liquefied petroleum gas tanks within the hold of a ship. The difiiculties encountered in providing an adequate support for an independent tank designed to transport liquefied petroleum gas (hereinafter referred to as LPG) at atmospheric pressure and low temperature are well known. Such tanks while on board ship are subjected to wide fluctuations in temperature and as a result there is substantial expansion and contraction of the tanks corresponding to such temperature fluctuations. Unlike a land-based storage installation, tanks of this type installed within the hold of a ship must be positively supported against forces induced by the motion of the vessel when underway. The tank must be prevented from shifting under all conditions of temperature fluctuation and all conditions of loading to which the tank is subjected when the ship is underway. The support therefor must provide for the expansion and contraction of the tank and yet must effectively prevent motion of the tank with respect to the ship under all conditions of temperature and motion.

Prior attempts to solve this problem included inclined wedges fitted between the ship side, longitudinal bulkhead and the LPG tank side, or keys fitted to the underside of the deck which mate with a keyway attached to the top of the LPG tank. Other arrangements include pads and crossed cables, hydraulic pistons and the like. The difficulty with all of the prior art type of supports is that each requires some form of attachment which is welded to the LPG tank sides or top to transfer the forces exerted through the welding to the internal tank structure. Furthermore, most of the known support methods require careful alignment. Here again, while careful alignment is no problem in a shore-based installation, it becomes difhcult if not impossible to obtain on board ship due to the fact that the ships structure is elastic and the vessels dimensions actually change when in the 'water over such dimensions when standing in the shipyard.

In order to solve the problem involved, it would appear desirable to utilize a support which is in some way precompressed between a structural portion of a ship and the sides of the LPG tank so that following cooling of the LPG tank due to filling with LPG, the support means would inherently elongate and continue to furnish the required support without allowing measurable deflection of the tank with respect to the ship during maximum roll or pitch.

Accordingly, it is the principal object of the present invention to provide a precompressed support for an independent LPG tank mounted within the hold of a ship which willcontinue to furnish the desired support for the tank throughout the complete range of shrinkage of the tank due to the cooling effect of the LPG carried therein.

Other objects of the present invention will be apparent from the following detailed description when read in conjunction with the attached sheet of drawings in which:

FIGURE l is a diagrammatic showing of an LPG tank mounted within the hold of a ship between opposed longitudinal bulkheads thereof; and

FIGURES 2A, 2B, and 2C are each diagrammatic sectional views of a support in accordance with the present invention, FIGURE 2A showing the support prior to prestressing, FIGURE 2B showing the support in its contracted and stressed state, and FIGURE 2C showing the same support in its final supporting condition.

In general, the objects of the present invention are achieved by providing a plurality of horizontal supporting members spaced around the side walls of an LPG tank, each supporting member being prestressed prior to assembly. The prestressing is achieved with materials readily available in any shipyard and does not require the application of any mechanical jacking force. Rather, the necessary prestressing is achieved by thermal shrinkage and elongation of the members in question.

FIGURE l shows an end elevation of an LPG tank 10 supported within the hold of a ship 12 and between opposite longitudinally extending bulkheads 14 and 16. The means furnishing the support which will be positive throughout the range of contraction of the tank 10 are indicated generally by the reference numerals 18 and 20 in FIGURE l.

Referring now to FIGURE 2A, it will be seen that the support includes a primary supporting member in the form of a horizontally disposed hollow pipe 22 which is closed at its inboard end by closure 24. The pipe 22 extends outwardly through an opening in the bulkhead 14. A guide means 26 may be utilized to properly position the pipe 22 with respect to the bulkhead 14 and the LPG tank. Surrounding the outer end of the pipe 22 is a secondary supporting member comprising a pipe 28 which is larger in diameter than the pipe 22 and is arranged concentrically therewith. The inboard end of the pipe 28 is welded or otherwise rigidly attached to the longitiudinal bulkhead 14. The outermost end of the pipe 28 is closed by an end cap 30 or other structural member which is also rigidly attached to the inner pipe 22. The annular space between the two pipes is filled with a heat-insulating material such as ordinary magnesia or asbestos.

The showing in FIGURE 2A while diagrammatic in nature, ind-icates the relationship between the various parts of the support and the side wall of the LPG tank prior to the prestressing operations which will be described hereinafter with reference to FIGURE 2B. Turning now to FIGURE 2B, this figure illustrates a method by which the overall length of the primary supporting pipe 22 may be shortened by thermal shrinkage and additionally positioned to move its innermost end a substantial distance outwardly from the side wall of the LPG tank. In order to accomplish this result without using any mechanical jacks or the like, the interior of the pipe 22 is filled with a coolant such as a mixture of alcohol and liquid oxygen. At the same time, heat from gas burners is applied to the exterior of the pipe 28. Obviously, the effect of the gas burners on the pipe 28 is to elongate the pipe 28 which in combination with the thermal shrinkage of the pipe 22 is sufficient to displace the inboard end of the pipe 22 a substantial distance from the side wall of the LPG tank. While in this shrunken condition, a heat insulating block made of Micarta or the like is positioned between the inner end of the pipe 22 and the side wall of the LPG tank. Once this block is in place, the burners are removed from the pipe 28 and the liquid coolant is withdrawn from the pipe 22 thus permitting both the primary and secondary supporting structures to return to ambient temperature. As they approach ambient ternperature, the pipe 22 will expand while the pipe 28 will contract and the net result is to exert a substantial force against the side wall ofthe LPG tank.

FIGURE 2C shows all the same parts shown in FIG- URES 2A and 2B but with the `further diagrammatic showing of the LPG tank iilled with cold liquid and with its side wall moved toward the center line of the tank and therefore displaced to the right from its position as shown in FIGURES 2A and 2B. The pipe 22, however, has continued to expand toward its normal length and maintains a positive loading force against the side wall of the tank.

By repeating the foregoing steps at a plurality of points around the periphery of the LPG tank, a positive support for the tank will be realized which is effective throughout the complete range of shrinkage and/ or expansion of the tank during actual use.

Since the LPG tanks are anchored to the vessels inner bottom, following lling with LPG, the tanks will shrink downward. Also, since the tank is anchored at its center point, it will shrink longitudinally toward its center or mid-length.

I claim:

1. A method of mounting an independent LPG tank in the hold of a ship, the steps comprising:

positioning a tank to be mounted within the ships hold and in spaced relation between opposed longitudinal bulkheads of the ship;

positioning a support member horizontally between lsaid tank and securing said member at its outer end to the outboard side of said bulkhead;

thermally shrinking said supporting member on its longitudinal axis;

inserting a rigid heat-insulating block between said supporting member and said tank while said supporting member is in its shrunken conditon;

permitting said supporting member to expand to wedge said block between said supporting member and said tank; and

repeating the foregoing steps at a plurality of locations on opposite sides of said tank.

2. A -method of mounting an independent LPG tank in the hold of a ship, the steps comprising:

(a) positioning a tank to be mounted within the ships hold in spaced relation to and adjacent a pair of longitudinal bulkheads of the ship;

(b) positioning a hollow pipe perpendicularly to a wall of said tank, said pipe extending freely outwardly through an opening in the related longitudinal bulkhead;

(c) concentrically surrounding the outboard portion of said pipe beyond said bulkhead with a second larger diameter pipe closed at its outer end to provide an enclosed annular space between said pipes, said second pipe abutting and secured at its inner end to said bulkhead;

(d) securing said closed end of said second pipe to the outer end of said first pipe;

(e) filling the annular space between said pipes with a heat insulating material;

(f) applying heat to the exterior of said second pipe while simultaneously supplying a coolant to the interior of said first pipe to shrink said first pipe and therefore move its inner end away from the Wall of said tank;

(g) inserting a heat insulating block of substantially rigid material between said rst pipe and the wall of said tank while said first pipe is in shrunk condition and its inner end spaced from said tank;

(h) removing the coolant from said first pipe and withdrawing the source of heat from said second pipe to permit said second pipe to contract and said iirst pipe to expand elastically into engagement with said insulating block to exert a mounting -force on said tank; and

(i) repeating the foregoing steps at spaced positions around said tank in order to hold said tank in a prestressed support to insure positive support following shrinkage of said tank which occurs when the tank is filled with LPG.

3. A method of mounting an independent LPG tank in the hold of a ship, the steps comprising:

(a) positioning the tank to be -mounted within the ships hold and in spaced relation between opposed longitudinal bulkheads of the ship;

(b) positioning a primary supporting member horizontally between said tank and extending freely outwardly through an aperture in the adjacent longitudinal bulkhead substantially half the total length of said member;

(c) surrounding the outer half of said supporting member with a secondary supporting member to define with said outer half an enclosed annular space, said second member being secured at its inner end to said bulkhead;

(d) filling the annular space between said supporting members with heat insulating material;

(e) closing the end of said secondary supporting member and rigidly securing said closure to the outer end of said primary and secondary members;

(f) thermally axially expanding said secondary supporting member while simultaneously thermally axially contracting said primary supporting member;

(g) inserting a rigid block of heat insulating material between the inner end of said primary supporting member and said tank while said supporting members are in their expanded and shrunken conditions;

(h) permitting said supporting members to return to ambient temperature so that said primary member elongates to less than its original length to wedge said block against the wall of said tank; and

(i) repeating the foregoing steps at spaced points on opposite sides of said tank whereby said tank -is positively held in the ships hold throughout the range of thermal shrinkage of the tank when it is later lled with LPG.

4. The combination with a ship having bulkheads running longitudinally of its hold, an LPG tank positioned within the hold, between and spaced from two of said bulkheads;

(a) a plurality of primary supporting members perpendicular to a wall of said tank, located at spaced points therealong, said members extending freely through apertures in said bulkheads;

(b) a plurality of heat insulating members one positioned between the inner extremity of each said primary supporting member and said tank;

(c) an equal number of secondary supporting members surrounding that portion of said primary members which extends beyond said bulkheads, said secondary members being secured at their inner ends to said bulkheads and at their outer ends to the outer ends of said primary supporting members, said primary supporting members and said heat insulating members being in compression due to thermal prestressing of said supporting members prior to assembly; whereby said supporting members exert a positive inwardly directed loading `force on the 5 f 6 walls of said tank throughout its range of shrinkage 3,339,782 9/1967 Segura. et al. 220-15 when lled with LPG. 3,355,051 11/ 1967 Kloeckner et al. 220-15 References Cited THBRON E. CONDON, Primary Examiner. UNITED STATES PATENTS 5 JAMES R. GARRETT, Asszslant Exwmmer.

2,825,547 3/1958 Vaughan. U-SC1- X-R' 3,080,086 3/1963 James 22o-15 114-74

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