The installation of Exxon's Lena guyed tower set two new offshore records when the longest one-piece jacket was positioned on the seafloor and eight main piles were driven to 560 feet. The overall installation of t!1e guyed tower jacket, decks, and pipelines required a variety of offshore installation procedures and extensive project planning. To minimize the potential for damage to the tower's guying system, an unconventional derrick barge mooring system was deployed at the installation site. A special pile latch assembly was developed to assist in installing six torsion piles. Installing 58 conductor strings required efficient handling of over 800 pieces of conductor pipe. Following deck installation, two pipelines were installed through 1000-foot J-tubes using the direct pull method and a dynamically positioned reel ship.

This paper was presented althe 9th Annual OTC in Housfon, Tex., May 2-5.1977. Tfiematerial is subjeclto correction by the ilutllor. Permission to copy is restricted to an'abstract of not more than 300 words. ABSTRACTIn offshore construction work related, to platforms, one of the difficult operations has been the connection of add-on sections to pin piles as they are driven into the sea floor. The reason for this difficulty has been the relative motion of the derrick barge and the fixed platform. This paper describes the design of and the application of a pile aligning system that makes this operation much easier to accomplish. It emphasizes the design of the system and its field operation conducted in the Gulf of Mexico. It descri bes the des i gn con,cepts, the actual hardware used to implement xhese concepts, and the successful operation of this hardware on the actual job site.

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