US3807179A

US3807179A - Deicing systems

Info

Publication number: US3807179A
Application number: US00294333A
Authority: US
Inventors: V Stone
Original assignee: Gulf Oil Corp
Current assignee: Chevron USA Inc
Priority date: 1972-10-02
Filing date: 1972-10-02
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30
Also published as: CA980588A

Abstract

Apparatus for protecting columns of offshore structures from dynamic forces of ice in which a plurality of upwardly movable ice-lifting elements are supported around the column and means are provided for moving the elements upwardly against the ice to break large blocks of ice from the icepack. The ice-breaking elements may be combined with inclined planes adapted to exert upward forces on the ice.

Description

[111 3,807,179 1451 Apr. 30, 1974 United States Patent 1191 Stone 7/1970 Roster et DEICING SYSTEMS 75 Inventor: Virgil D. Stone, Miami, Fla. 6/1972 [73] Assignee: Gulf Oil Corporation, Pittsburgh,

Primary Examiner-Jacob Shapiro [22] Filed: Oct. 2, 1972 [21] Appl. No.: 294,333

- ABSTRACT 'Apparatus for protecting columnsof offshore struc- [52] U S C 61/1 1 61/46 14/40 tures'frorh dynamic forces of ice inwhich a plurality 51] 17/60 B63b 35/08 of upwardly movable ice-lifting elements are sup- 58] Fieid 61/1 46 A 5 1 14/40 ported around the column and means are provided for l 7; 'moving the elements upwardly against the ice to break large blocks of ice from the icepack. The ice-breaking elements may be combined with inclined planes References Cited adapted to exert upward forces on the ice. UNITED STATES PATENTS 10 1972 3,696,624 Bennett.......................... 1;. 61/46 8 Claims, 3 Drawing Figures PATENTEmrnso m4 SHEEI 1 BF 2 Fig DEICINGSYSTEMS This invention relates to offshore structures for use in arctic regions and more particularly to apparatus for protection of columns supporting such structures from same. Major overturning forces-and shearing stresses can be imposed on the structures by this ice. Land-fast ice, usually found within 5 to 50 miles of the shore line, may develop a thickness of up to approximately 7 feet. Although appearing stationary, thisthick sheet of ice may move laterally because of expansions and contractions causedby temperature changes and also the force of winds and currents at sea. Experiments indicate that the movement of the ice can exceed several hundred yards in just one day. Structural columns erected in these seas, therefore, are exposed to the full crushing strength of ice (several hundred pounds per square inch) actingover a vertical distance of several feet in certain circumstances.

Still more rigorous conditions are imposed on offshore structures by pack-ice" or pressure ridges within land-fast ice. Under these circumstances the ice forces may be of a magnitude larger than those found in ordinary land-fast ice because the mass of ice may be many times thicker, up to 50 feet or more from top to bottom. The ice also may be older and consequently stronger in terms of pounds per square inch, and it may move at greater speeds. The capacity of pressure ridges in land-fast ice for upsetting the structural integrity of offshore platforms therefore can be very great.

Several methods havebeen proposed for protecting offshore structures from ice; It has been suggested that sleeves be supported around the supporting columns of the structure and the space between the sleeves and columns be filled with a liquid having a very low freezing point in the belief that by surrounding thecolumn with liquid will isolate the column from the forces exerted by the ice. Another method for accomplishing the same purpose has been to support around the-column a sleeve having a length adequate to extend into water that is above the freezing point. The sleeve. conducts heat from the warmer water to prevent ice formation betweenthe sleeve and the column; The use of such sleeves to protect columns is disclosed in U.S. Pat. Nos. 3,370,432 and 3,170,299. Even if the sleeves do prevent ice formation between the columns and the sleeves,'the ice pack will press against the sleeves and such forces are necessarily transmitted from the sleeves to the columns through whatever structure supports the sleeves.

U.S. Pat. No. 3,669,052 describes apparatus for protecting columns of offshore platforms utilizing rapidly moving chipping elements that strike the vertical face of the ice pack adjacent the column. Breaking of the ice is accomplished by a large number of rapid impacts that induce stresses in a small area adjacent the point of impact. Delays in operation-of the apparatus could, by the ice pack moving forcefully against stationary chipping elements, make starting of the device impossible.

U.S. Pat. Nos. 3,405,527 and 3,436,920 describe structure for protecting offshore structures from float- .ing ice such as icebergs. The structure disclosed in those patents is not suitable when the ice is in the form of a packed continuous mass which cannot readily be diverted from the structure as can free-floating ice.

In U.S. Pat. No. 2,449,463, an inclined slot through ice adjacent a darn with a sheet member in the slot is disclosed for protection of dams from the forces exerted by the ice as the ice expands because of an increase in temperature. The structure can be effective when the ice is substantially stationary, and it is only necessary to relieve compressive forces within the ice.

The inclined cuts would not be effective to relieve forces exerted by a continuous supply of ice moving toward the offshore structure.

This invention resides in amethod and apparatus for breaking moving sheet ice on the surface of water surrounding off-shore structuresin which the ice adjacent the structure is lifted to exert a bending moment placing the ice under tension to break large pieces from the sheet ice. A downwardly slopingsurface extends outwardly from the structure under the sheet ice to lift the ice as the ice moves toward the structure. In a preferred form of the invention ice breaking arms located at intervals around the inclined surface reciprocate upwardly preferably from recesses in the inclined surface to increase the bending moment and concentrate the stresses applied to the ice.

- In the drawings,

FIG. 1 is a diagrammatic elevational view of an offshore platform supported by a'singlecolumn having one embodimentof this invention-for the protection from ice.

FIG. 2 is a diagrammatic view in elevation showing pivotally mounted arms in combination with an inclined apron adapted to .lift the ice.

FIG. 3 is a diagrammatic view in elevation of an em-, bodiment similar to that'illustrated in FIG. 2 but in which the arms are pivotally supported at their upper Referring to FIG. 1 of the drawings, a platform indicated generally by reference numeral 10 is-supported above the surface 12 of a body of water by a single column 14.Column14is secured at its lower end toa base member 16 which'is preferably secured to the sea floor l8'by suitable piling 20. Supported on column 14 substantially at the level of the water surface 12 is the deicing apparatus indicated generally by reference numeral 22 of this invention. 1

Platform 10 is illustrated in FIG. 1 with a-drilling rig 24 mounted on its deck'and with a plurality of walls 26 extending downwardly through column 14 into the sea 1 floor. This invention isnot restricted to platforms used to support drilling rigs. The invention is suitable for the protection of any types of offshore structures in cold regions in which the structures may be exposed to dynamic forces of land-fast ice. For convenience in illustration, the apparatus is shownwith a platform supported by a single column which may have a diameter up'to about 30 feet. This invention is also of value in protecting structures supported by a plurality of columns. If used with structures supported by multiple columns, it will be necessary to provide the apparatus 22 on each of the columns to obtain full protection against the dynamic forces of ice.

In the apparatus illustrated in FIG. 1, the ice packing apparatus includes a sleeve 26 surrounding column 14 and secured thereto a short distance above the surface of the ice by suitable bolts 28. Mounted on the outer surface of sleeve 26 are a plurality of hydraulic cylinders 30 having pistons, not shown, slidable therein. Hydraulic fluid lines 32 extend from the platform to the hydraulic cylinders 30 to actuate the pistons in the cyl inders. Hydraulic cylinders 30 have conventional valving to cause reciprocation of the pistons in the cylinder.

Extending downwardly from the pistons in cylinders 30 are connecting rods 34 which are attached at their lower end to a ring 36 slidably encircling column 14. Ring 36 has an inclined upper conical surface 38 sloping downwardly and outwardly from the sleeve 26 and an inclined lower surface 40 sloping upwardly and outwardly from its lower end.

In the operation of the embodiment of the invention illustrated in FIG. 1, the hydraulic fluid delivered to the hydraulic cylinders 30 causes reciprocation of the pistons within the cylindersrThe pistons drive connecting rods 34 and thereby cause reciprocating vertical movement of ring 36. Upward movement of the ring lifts and breaks the ice adjacent column 14 from the sheet of ice. The largest'tension forces .are induced in the ice radially beyond the ring 36. Breaking of the ice will normally occur at the location of the largest tension forces and thereby clear ice around the column. Downward movement of the ring to a position such that the upper surface of the ring is below the lower surface of the ice is not, therefore, ordinarilyimpeded by sheet ice. By continuously. breaking the ice adjacent the column, the column is protected from the dynamic forces that would be exerted against the column by moving ice.

In the apparatus illustrated in FIG. 2, pivotally mounted arms 42 are mounted in a conical steel apron 44 encircling column 14 and extending outwardly to position the outer edge below the level of the bottom surface of the sheet ice. Arms 42 pivot about their upper ends. Suitable actuating devices such as hydraulic cylinders 46 engage arms 42 near their lower end to reciprocate the lower end of the arms. Ice approaching column 14 engages the conical apron 44 and is lifted to place the lower surface of the sheet ice in tension. Upward movement of the lower ends of arms 42 increases the tension in the ice and breaks from the ice pack. While the apparatus has been illustrated in FIG. 2 with the arms 42 pivoting about their upper end, the arms 42 could pivot about their lower end and have driving means at their upper end for lifting the arms above the conical surface 44. The elevation of the apparatus can be adjusted by means of pins 48 that extend through a collar at the upper end of apron 44 into holes 50 in the column.

In the apparatus illustrated in FIG. 3, arms 52 are pivotally mounted at their upper ends on the outer surface of sleeve 54 which is suspended by cables from the platform. Actuating devices 56, preferably hydraulic cylinders, cause back and forth movement in a radial direction of the lower ends of the arms 52. The arms engage ice surrounding the column 14 and tendto lift the ice to break it free from the pack. The lifting of ice produces a bending moment that places ice along the bot- -4 tom of the ice sheet in tension radially outwardly from the arms. The weakness of the ice in tension facilitates breaking the ice.

The apparatus of this invention makes use of the low tensile strength of ice in tension to cause breaking of large blocks of ice from the pack. ice. As the ice is lifted above the water and is no longer supported by the water, the weight of the ice places the bottom layers of the ice in tension. Additional tension results from movement of the pack ice toward the apparatus which exerts a force tending to bend the ice around a fulcrum in the upper portion of the ice. Each of the embodiments of the invention is suitably supported on the col umn it is designed to protect'in a manner that permits vertical adjustment of the apparatus as required to locate the apparatus properly for changes in tide.

I claim:

1. Apparatus for protecting supporting columns of offshore structures from ice comprising a vertically adjustable supporting sleeve surrounding the column, ice

breaking means mounted on, the sleeve and extending outwardly and downwardly around the sleeve toa level at the outer periphery of said ice breaking means below the lower surface of the ice, and means for reciprocating the ice breaking means from a lower position below the lower surface of the ice to an upper position .to lift ice surrounding the column to place the lower surface of the ice in tension and break the ice.

2. Apparatus as set forth in claim 1 in which the means for reciprocating the ice breaking means comprise hydraulic cylinders and connecting rods actuated by the-cylinders and connected tothe ice breaking means to reciprocate the ice breaking means.

3. Apparatus as set forth in claim 1 in which the ice breaking means comprise a ring surrounding the sleeve and vertically movable with respect thereto, said ring having an outwardly and downwardly sloping upper surface. j

4. Apparatus as set forth in claim 3 in which the ring has a lower surface sloping downwardly and inwardly from its outer edge.

5. Apparatus as set forth in claim 1 in which theice breaking means comprise an apron having an upper surface extending outwardly and downwardly to position the perimeter thereof below the lower surface of the ice,-a plurality of arms pivotally mounted in the apron around the circumference thereof, and the reciprocating means are connected to the arms'to move the arms from a lower position recessed in the apron to an upper position above the upper surface of the apron.

6. Apparatus as set forth in claim 5 in which the arms are mounted to pivot about their lower end.

7. Apparatus as set forth in claim 5 in which the arms are mounted to pivot about their upper end.

.8. Apparatus as set forth in claim 1 in which the ice breaking means comprise a plurality of pivotally mounted arms positioned at substantially uniform intervals around the circumference of the sleeve, and the means for reciprocating are secured to the ends of the arms remote from the pivotal mounting for reciprocating the arms about the pivotal mounting from the lower position below the lower surface of the ice to the upper position.

*. Ir k

Claims

1. Apparatus for protecting supporting columns of offshore structures from ice comprising a veRtically adjustable supporting sleeve surrounding the column, ice breaking means mounted on the sleeve and extending outwardly and downwardly around the sleeve to a level at the outer periphery of said ice breaking means below the lower surface of the ice, and means for reciprocating the ice breaking means from a lower position below the lower surface of the ice to an upper position to lift ice surrounding the column to place the lower surface of the ice in tension and break the ice.

2. Apparatus as set forth in claim 1 in which the means for reciprocating the ice breaking means comprise hydraulic cylinders and connecting rods actuated by the cylinders and connected to the ice breaking means to reciprocate the ice breaking means.

3. Apparatus as set forth in claim 1 in which the ice breaking means comprise a ring surrounding the sleeve and vertically movable with respect thereto, said ring having an outwardly and downwardly sloping upper surface.

5. Apparatus as set forth in claim 1 in which the ice breaking means comprise an apron having an upper surface extending outwardly and downwardly to position the perimeter thereof below the lower surface of the ice, a plurality of arms pivotally mounted in the apron around the circumference thereof, and the reciprocating means are connected to the arms to move the arms from a lower position recessed in the apron to an upper position above the upper surface of the apron.

8. Apparatus as set forth in claim 1 in which the ice breaking means comprise a plurality of pivotally mounted arms positioned at substantially uniform intervals around the circumference of the sleeve, and the means for reciprocating are secured to the ends of the arms remote from the pivotal mounting for reciprocating the arms about the pivotal mounting from the lower position below the lower surface of the ice to the upper position.