Analysis Of Ocean Engineering Problems In Offshore Pipelining
Authors: Blumberg Randolph , Osborn Charles , Taher Samir A. 
Published: October 2008

Millions of dollars are lost and the safety of pipe lining personnel and equipment is jeopardized each year because of inadequate appreciation for the ocean engineering problems in offshore pipelining. The rapid increase in demand for oil and natural gas in the United States and the rest of the free world has greatly expanded the need for more offshore pipelines and gathering facilities in deeper ocean waters. As pipeline diameter and water depth increase, the problems of successful installation of these gathering facilities go up exponentially.

Ocean engineering problems discussed were developed from theoretical studies and engineering field monitoring of pipelaying operations in the Gulf of Mexico by American Science & Engineering Company engineers. Pipeline monitoring was performed for a variety of lay barge-stinger combinations used by three major pipeline contractors in laying pipelines ranging up to 36 inches in diameter in water depths out to 320 feet. Total value of these pipelines is well in excess of $100 million.

Ocean engineering problems reviewed include an analysis of the fourth order nonlinear differential equations which govern pipe bending stresses during laying operations and calculation of davit lifting schedules so that the Submerged pipe may be safely raised for tie-ins and riser connections. Instrumentation which has been successfully used to measure barge motion and subsurface ocean currents is described. Systems engineering is discussed with reference to typical problems such as equipment dependability. The old adage "For want of a nail the shoe is lost ---" has its parallel in offshore pipelining, since relatively small mechanical problems curtail pipelining operations for extended periods of time at great economic loss. Barge anchoring, stinger configuration, pipeline tension, bottom conditions, communication problems, and the importance of an adequate knowledge of weather and environmental forecasts are discussed as part of the system's engineering. Human engineering is shown to play a vital role in successful offshore pipelining.

Introduction

Rapid increase in demand for natural gas in the United States has greatly increased the need for offshore pipelines and gathering facilities in deeper waters of the continental shelf of the Gulf of Mexico. As pipeline diameter and water depth increase, the problems in successful installation of these gathering systems go up exponentially. For these deeper waters, an adequate analysis of the fourth order nonlinear differential equations must be made to determine stresses in the pipeline. This is in contrast to shallow water pipelining operations where typical rule of thumb methods can be successfully employed.

This paper presents the results of theoretical studies and field monitoring of various pipelining operations in water depths out to 320 feet and for pipe diameters up to 36 inches. The authors'; attempt to categorize the ocean engineering problems involved in the laying of pipelines is based on both their own field experience and that of their colleagues. This experience has been largely gained during the period 1967-1970 while performing engineering field monitoring of pipeline operations for various lay barge stinger combinations belonging to Brown & Root, McDermott, and Houston Contracting.