A New Offshore Pile Aligning System
Authors: Boyadjieff George , House Horace , Roussel Herbert 
Published: December 2007

This paper describes the design and application of a pile aligning system that makes connecting add-on sections of piles in offshore platforms easier. Field operation of the system in the Gulf of Mexico is discussed. Design concepts, actual hardware used to implement these concepts, and successful operation of hardware on the job site also are discussed.

Introduction

Steel platforms are conventionally pinned to the ocean floor with large-diameter piling, which is driven through the legs of the platform and/or through guides around the base of the platform. When platforms are set in deep water, it is not feasible to handle the pipe in one section. It is necessary to add on additional sections as the pile meets and then is driven into the ocean floor. The platform itself is grounded to the sea bottom, whereas the derrick associated with a derrick barge for handling the add-on pile sections floats on the ocean surface. Consequently, there is relative motion between the section of piling to be added and the pile that already has been installed in the leg or guides around the platform. The amount of motion is, of course, a function of the wave action or sea state on the derrick barge. When the weather becomes a factor, it is common to wait for calm seas, even though the operation may cost as much as $50,000/day while waiting.The piling used today is either 48- or 54-in. diameter and some is more than 90 in. The add-on sections usually are joined to the pile by welding. Because welding must be performed in the field, it takes 3 to 12 hours or longer per connection, depending on wall thickness. Time is per connection, depending on wall thickness. Time is saved by using mechanical connectors that theoretically eliminate welding time and pay for themselves, even though they may never be recovered. On the other hand, experience to date has proven that with the motion, it is impossible to align the connectors and connect them successfully. Sometimes the operation takes longer than welding; therefore, these connectors are used reluctantlyWhen pile is driven through guides around the base of the platform (skirt piles), sometimes it must be cut off at the base of the platform to remove the upper section. Upper sections of pile are not necessary to improve jacket stiffness and, thus, considerable savings result. When the upper section of the driven pile must be removed, we need a disconnector at the appropriate level, which usually takes the form of the described mechanical connectors. During removal these upper pile sections must be held as well as disconnected. This study describes a way to speed up connecting time and make it more feasible to use mechanical connectors where possible.

Design Solution

The crux of the problem is the relative motion between the add-on pile and the pile already installed in the jacket. Eliminating this relative motion results in a satisfactory solution to the problem. Among secondary advantages of using mechanical connectors would be the ability to rotate the piling for connecting and disconnecting. Also, if the pile could be lowered or raised independently, several piles could be run simultaneously. This could result in piles could be run simultaneously. This could result in significant time savings for the over-all operation.The proposed solution to these problems is called the Pile Aligning System (PAS). PAS has four components: Pile Aligning System (PAS). PAS has four components:the aligning structure (Fig. 1),the self-powered hydraulic power supply (Fig. 2),the pickup elevator. andthe driving head (Fig. 3).

JPT

P. 1061