New Pile Handling Techniques

Abstract

Summary The handling of large-diameter piling has not changed since the inception of the offshore construction industry. The hazards, as well as the time loss, associated with conventional techniques never have been questioned until recently. A newly developed set of automatic gripping and holding tools has transformed pile handling from a brute force, manual, labor-intensive operation to a remotely controlled automatic grip or release operation. Introduction As well depths increase, steel platform structures increase in height and in base dimensions. Concurrently, pin piles basically have become larger in diameter and longer, resulting in heavier strings of piling. This in turn has necessitated larger shackles to support the hoisting load and corresponding pad eyes welded to the piles for attaching the shackles. As a result, handling piles from the material barge to the platform under construction has become harder to accomplish and has required a longer time to accomplish. For each add-on section of piling, it is not uncommon to spend several hours removing the pad eyes once the pile connection has been made. This time-consuming task, which has to be repeated for each section of add-on piling, has become a significant part of the construction cost, particularly as more piles are required on deep structures to pin the jacket to the ocean floor.In 1973, the first North Sea structure containing large numbers of skirt piles was being designed for the Forties field. It was felt by the designers that conventional pile-handling methods would result in prohibitive construction costs, and they sought an alternative, more economical, way of gripping and holding on to the pile. Field operators approached us to develop a method for handling large-diameter piling. We were able to take basic casing handling equipment, which required no pad eyes or external protuberances on the pipe, and adapt it to the larger-diameter piles. The largest previously manufactured casing handling tools could handle a maximum diameter of 20 in.The first set of pile-handling tools was designed to grip 54-in. OD piling. These large-diameter tools, or spiders as they are called, borrowing nomenclature from similar casing-handling equipment, were used on the Forties field platform and then on what was then the world's deepest platform constructed in the Santa Barbara Channel in the Hondo field.The development of these tools and their subsequent improvements, as well as their uses, are the subjects of this paper. Description of Previous Methods When platforms were constructed in shallow water, it was generally possible to pick up the intended pin piles in one section and lower them to the ocean floor through the jacket legs. Since there were no known methods of gripping the OD of a smooth round pipe of this size, it was natural for early construction contractors simply to weld pads onto the outside of the piling and to attach slings and shackles to it so that it could be picked up by the crane on the derrick barge. Since these smaller, shorter sections of piling were fairly light, the shackles and stings posed no particular handling problem, and it was quite expedient once the pile had reached the mudline to cut off those pad eyes with a cutting torch. Similarly, if additional sections of piling had to be added to the string as it was driven into the mud of the ocean floor, these add-on sections would be picked up and stabbed into the initial pile, and then would be welded together.As construction jobs became more complex, it was desirable to use the derrick barge came for other tasks while this welding process was performed. JPT P. 2455^