Pile Splice

Abstract

A machined pile splice for use in construction of offshore platforms. A box member is attached to a pile member before it is driven. A pin member is attached to the pile section to be added. A shear ring is located in opposing recesses in both the box and pin members. The shear ring is made slightly wedge-shaped in cross section and is initially installed in the box member where it is held centered by a corrugated spring strip. The box member is also provided with thread studs which force the shear ring into tight contact with the lower surface of the pin member recess and upper surface of the box member recess. The outer surface of the pin member and the inner surface of the box member are tapered. The tip of the pin member passes through the shear ring and outer wall of the pin member contacts the inner wall of the shear ring. As the tapered pin member continues through the shear ring, the ring is forced to increase in diameter which forces the ring deeper into the box member recess. After the pin member is fully inserted into the box member, the shear ring snaps out of the box member and into the opposing pin member recess. The thread studs are screwed in, forcing the wedge-shaped shear ring into tighter contact with the lower surface of the pin member recess and the upper surface of the box member recess. An O-ring is provided between the pin and box members to provide a fluid seal.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally concerns method and apparatus for use in splicing pile sections. MOre particularly, the invention concerns using spliced pile sections in the construction of offshore platforms.

2. Description of the Prior Art

The erection of an offshore platform of the jacket type commonly used by the oil industry involves three principle phases: (1) launch the lower jacket and set it on bottom; (2) install piling and connect the piling to the lower jacket; and (3) install deck units and connect the deck units to the piling. Of these three phases, installation of the piling normally consumes over 75 percent of total erection time. Installation of a piling can be subdivided into four principle operations: (1) placing the pile sections; (2) welding the pile sections together; (3) driving the pile sections; and (4) connecting the pile sections to the lower jacket. Of these four operations, welding the pile sections together normally consumes about 33 percent of the total pile installation time

Current standard practice for pile installation provides for prefabrication of each pile into two or more sections, depending on the total length of pile required. The length of each individual section of pile is primarily dependent on the boom length of the crane on the derrick barge used in the pile installation. All pile sections, except the lead section, are equipped with an alignment or stabbing guide to aid field installation. This guide serves several functions. First, to expedite alignment of the pile section being added with previously driven pile section; second, to support the added pile section in position while the pile sections are being welded together; and third, to serve as a backing ring for welding purposes.

During field installation, the crane operator swings the pile section being added over the previously driven pile section. When the pile section being added is in approximate alignment with the driven pile section, the crane operator lowers the section being added to insert the stabbing guide into the top of the receiving or previously driven pile section. As the section to be added is lowered, the guide forces the pile sections into approximately proper alignment. When the stabbing guide is fully inserted into the top of the driven pile section, the crane operator slacks off on the crane load line to allow the guide to take over support of the added pile section. This sequence proceeds smoothly during calm seas, but during moderately rough seas, it is not unusual for the roll of the derrick barge to result in pulling the stabbing guide completely out of the top of the driven pile. When the pile section being added is in place and fully supported by the stabbing guide, the pile sections are checked for alignment before welding is started. Since most offshore platform piles are driven on a batter, and since piles and stabbing guides are fabricated from pipe with standard industry-accepted dimension tolerances, it is quite common for these pile sections to be out of alignment as a result of the movement exerted on the stabbing guide by the weight of the pile section. Such misalignment is commonly corrected by rotating the pile section to be added to the "best fit" for matching roundness of the pile sections, measuring the center line misalignment, removing the pile section, adding a heel plate on the high side of the stabbing guide to use the guide's length as a lever to force correct alignment and then restabbing the pile section to be added.

The machined pile splice described herein will mitigate or eliminate these important time-consuming installation problems. As soon as the pin is completely inserted in the box, the shear ring snaps into position and prevents unseating if the derrick barge rolls due to sea action. Since both box and pin are machined to relatively close tolerances, misalignment is not encountered.

SUMMARY OF THE INVENTION

The pile splice of the present invention eliminates welding pipe sections together during pile-driving operations. During rough sea conditions, this pile splice reduces the time required to place the pile sections subsequent to placement of the lead pile section. This pile splice comprises a box and pin connection similar to drill pipe tool joints, but without threads. These connections are welded to pile sections during land phase fabrication. A shear ring located in opposing recesses in both the box and pin acts in lieu of threads. The shear ring is made slightly wedge-shaped in cross section and is initially installed in the box where it is held centered by a corrugated spring strip. The box is also equipped with thread studs which force the shear ring into tight contact with the lower surface of the pin recess and the upper surface of the box recess.

In makeup of this connection, the pin is inserted into the box. The outer surface of the pin and the inner surface of the box are tapered. The tip of the pin passes through the shear ring and the outer wall of the pin contacts the inner wall of the shear ring. As the tapered pin continues through the ring, the ring is forced to spread and increase in diameter. This forces the ring deeper into the recess in the box which, in turn, causes the corrugated spring strip to flatten out. After the pin is fully inserted into the box, the shear ring snaps out of the box recess and to the opposing pin recess. All thread studs are then screwed in forcing the wedge-shaped shear ring into tighter contact with the lower surface of the pin recess and the upper surface of the box recess. Such wedge action causes tight contact between the end of the box and the shoulder of the pin. When this connection is completely made up, the tight metal-to-metal contact between the end of the box and the shoulder of the pin transmits compressive load and driving energy between the pile sections. The shear stress developed in the shear ring transmits tensile load between pile sections.

By appropriate sizing and selection of grades of steel, this connection can be designed to resist all required stresses that the pile will be subjected to. (Piles for jacket-type offshore platforms are not subjected to torsion.)

Aside from the obvious advantage of reducing water phase erection cost by reducing the time required to install piling, there is a functional advantage resulting from reducing the time required to drive a pile or more particularly, for reducing the downtime between periods of actual pile driving. The static capacity of soil is greater than its resistance to driving. When pile driving stops, the soil's grip starts increasing so that resistance to driving is greater when pile driving is resumed than it was when pile driving ceased; the longer the period of downtime, the greater the initial resistance to resumption of driving. Consequently, with a certain set of conditions (available hammer energy, required total pile penetration, depth of penetration to the last splice, and the time rate of soil capacity increase), excessive downtime to add a pile section might result in inability to drive the pile to a desired depth of penetration resulting in reduced pile capacity. The pile splice of the present invention allows the design of deeper pile penetrations and greater capacity when these conditions exist.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the pile splice made up in accordance with the present invention;

FIG. 2 is a cross section through the box illustrating the arrangement of the box, spring strip and shear ring prior to insertion of the pin; and

FIG. 3 is an isometric view of the shear ring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown the top of a driven pile section 10 and the bottom of a pile section 11 to be added. Pile section 10 is welded as at 12 to a box member 13 provided with a recessed portion 14 and a series of threaded openings 15 extending from the outer surface into the recessed portion 14. An O-ring seal 16 is arranged on the inner surface of box member 13. Pile section 11 is welded as at 20 to a pin member 21 provided with a recessed portion 22 which opposes recess 14 in box member 13 when the pin member is fully inserted into the box member. The outer surface 23 of pin member 21 is tapered downwardly an inwardly and the inner surface 24 of box member 13 is tapered upwardly and outwardly. A shoulder 25 formed on pin member 21 engages the upper end 26 of box member 13. A shear ring 30, shown also in FIGS. 2 and 3, is arranged in recesses 14 and 22. A threaded stud 31 protrudes through each threaded opening 15 and bears against shear ring 30.

As shown, a corrugated spring strip 35 is arranged between shear ring 30 and box member 13. In operation, pin member 21 is inserted into box member 13. As the tip of pin member 21 passes through shear ring 30, the outer wall 23 of the pin member contacts the inner wall of shear ring 30. As pin member 21 continues through shear ring 30, the ring is forced by the tapered wall 23 to spread and increase in diameter. In this manner, the shear ring is forced deeper into recess 14 which in turn causes the corrugated spring strip 35 to flatten out. After the pin member is fully inserted into the box, as illustrated in FIG. 1, shear ring 30 snaps out of the box member recess 14 and into the opposing pin member recess 22. The thread studs 31 are then screwed in threaded openings 15 to force the wedge-shaped shear ring 30 into tighter contact with the lower surface of the pin member recess and the upper surface of the box member recess. Such wedge action forces tight contact between the end of the box member and the shoulder of the pin member.

Various modifications may be made in the preferred embodiment of the invention which have been described without departing from the spirit and scope thereof.

Claims

Having fully described the objects, advantages, apparatus and method of my invention, I claim:

1. A pile splice comprising:

a pin member attached to one pile section, said pin member having an outer shoulder, a tapered outer surface, an inclined lower end and a recess formed therein;

a box member attached to another pile section in which said pin member is insertable, said box member having an end engageable with said pin member shoulder when said pin member is fully inserted in said box member, said box member also having a tapered inner surface and recess formed therein, said pin member and box member recesses opposing each other when said pin member is fully inserted in said box member;

a shear ring initially arranged in said box recess and adapted to snap into said pin member recess and engage one surface of said pin member and an opposite surface of said box member when said pin member is fully inserted in said box member, the depth of said box member, the depth of said pin member recess being less than the thickness of said shear ring;

means associated with said shear ring for urging said shear ring to snap into said pin member recess; and

spring means for wedging said shear ring against said one surface of said pin member recess and said opposite surface of said box member recess when said pin member is fully inserted in said box member, said wedge action causing tight metal-to-metal contact between the end of said box member and said shoulder of said pin member.

2. A pile splice as recited in claim 1 in which said spring means for urging said shear ring to snap into said pin member recess includes a corrugated spring strip initially arranged in said box recess between said shear ring and the wall of said box recess.

3. A pile splice as recited in claim 2 in which said means for wedging said shear ring includes:

a plurality of spaced-apart threaded openings extending from the outer surface of said box member to the interior of said box recess; and

thread studs extending through each of said threaded openings, said thread studs abutting said shear ring to wedge said shear ring against said one surface of said pin member recess and said opposite surface of said box member recess when said pin member is fully inserted in said box member.

4. A pile splice as recited in claim 3 in which the surfaces of said shear ring which engage said surfaces of said recesses are tapered.

5. A pile splice as recited in claim 4 including an O-ring seal arranged between said pin member and box member.