During the past year, a new mechanical pile connector has been introduced to the offshore construction industry. This connector has been the culmination of an extensive development and fullscale testing program by Vetco Offshore, Inc. A family of driveable pile connectors has since been produced, ranging In size from 30" O.D. to 72" (762 mm to 1829 mm). produced, ranging In size from 30" O.D. to 72" (762 mm to 1829 mm). Included in this family are standard releasable connectors and remote-releasable connectors for skirt pile recommended for permanent pile applications.
Specifically designed for skirt pile and permanent pile applications, the pile connector incorporates field-proven features that have been used on pile connector incorporates field-proven features that have been used on Vetco wellhead and riser connectors. The design phase included a finite element optimization and a fatigue analysis of the connector. Special anticorrosion considerations have been taken to ensure long life in the marine environment.
The connector was tested extensively at both in-plant and field facilities. These tests included tensile, pressure, bending functional, and pile driving tests. Following the development tests, the connector was supplied to several users for actual field trials. Since the connector has been introduced to the offshore industry, it has been used in a variety of skirt piles and permanent pile applications. To date, the pile connector has been piles and permanent pile applications. To date, the pile connector has been supplied in 30",40", 42", 48", 54" and 72" (762 mm, 1016 mm, 1067 mm, 1219 mm, 1372mm and 1829 mm).
It has been found that the handling, stabbing, and connecting of individual pile sections often represents a critical phase during offshore construction. These operations are particularly acute during heavy weather conditions. Considerations for men and machinery safety often dictate a work slowdown. or even a stoppage, until a suitable weather window is available.
In addition, a significant amount of time is consumed during pile welding operations. Weld time must include pile pile welding operations. Weld time must include pile positioning, preheat, welding, cool-down and inspection. For positioning, preheat, welding, cool-down and inspection. For welding larger diameter, heavy-wall pipe sections, these welding operations become increasingly time-consuming and expensive. Recognizing these increased costs of offshore welding and rig time. Vetco has developed a mechanical connector for large diameter pile sections (Figure 1). The Vetco Pile Connector is a heavy-duty, driveable connector designed specifically for connecting sections of drive string, platform piling and other large diameter applications. It is a thread less connector and does not require rotation for makeup. When made up, the connector provides a strong, pressure-tight and rigid connection which efficiently transfers the driving energy throughout the length of the piling string. This results in a faster, more economic driving operation. Since the pile connector is preloaded during makeup, this condition greatly enhances the preloaded during makeup, this condition greatly enhances the fatigue strength of the joint, ensuring that it has longer fatigue life than the basic pile section. The design and materials of the connector have been carefully considered to ensure that it has maximum corrosion resistance and is suitable for application in a permanent offshore installation.
During the pile connector design phase, experience gained from producing several other field-proven mechanical and hydraulic connectors was utilized. In particular, Vetco's long experience in marine drilling riser connectors and subsea hydraulic connectors was used to adapt several successful features to the pile connector.
This paper presents a technical description of the Vetco Pile Connector. In doing so, it describes the development of the connector from design through prototype testing and field application stages.
The standard releasable pile connector, illustrated in Figure 1. comprises a pin member and a box member with an interlocking dog arrangement to ensure a positive preloaded connection.
During installation, an individual pile joint would normality be run in a box down, pin up configuration. As the box is stabbed over the pin of the previously run pile, the tapered conical internal surface of the box permits easy engagement. No rotation or axial alignment is required at any time. When the box section has seated on the pin drive shoulder, the actuating screws are then rapidly driven in by impact wrench. This action, as illustrated in Figure 2, drives the locking dogs in to mate with corresponding groove rings on the pin member. In doing so, the tapered surface of the dog threads contacts the corresponding pin groove taper, creating a preloaded condition. Typically, a torque value of 600 ft.-lbs. (813.6 N.m) is used as the impact wrench setting. A locking plate arrangement is provided which ensures that the actuating screw cannot back out during subsequent driving. The weight of the impact wrench depresses the spring-loaded locking plate when the wrench socket is installed on the actuating screw head. When the locking plate is depressed, the actuating screw may be made up. Removing the impact wrench permits the locking plate to spring back and trap the hexagonal actuating screw head.
Since, however, the connector is omnidirectional, it may also be run in a pin down, box up configuration if a stab guide is used (see Figure 6). The connector performance is unaffected by its orientation.