A Concept for Design of Submarine Pipelines to Resist Ocean Forces

A philosophy for design of submarine pipelines on the seabed to resist ocean forces is proposed. According to it, the pipeline response to hydrodynamic forces is calculated and the predicted response parameters are compared with the permitted values given by the design criteria. Some guidelines are given to achieve compatibility of individual elements in the design procedure. Introduction Need for an Improved Design Procedure. The importance of a safe and economic design of pipelines on the seabed in respect to the in-place stability has been widely recognized. An increasing number of pipelines approved by the certifying authorities for deployment directly on the seabed without subsequent trenching or other means of protection, urges the need for a more reliable design procedure. In the current engineering practice, however, mistakes or inconsistencies are often seen in the design of pipelines. The aim of pipeline design in respect to the in-place stability is determination of steel pipe thickness and weight of concrete coating. Even small changes in the concrete coating thickness or weight may pose significant impact on the entire pipeline project. The weight of the concrete cover is a decisive factor for the accomplishment of satisfactory pipeline stability and it may prove to be the decisive factor for the carrying out of the installation. In such a case, when the installation cannot be accomplished due to too great pipeline weight, a conceptual change, having significant consequences for the entire project, is the only solution, e.g., pipeline burial or re-routing of the line. Purpose of This Paper. The aim of this paper is to present a concept for a design procedure of pipelines in respect to the in-place stability during action of hydrodynamic forces and to give guidelines for the treatment of individual elements in the design procedure which ensures compatibility of these elements with the procedure. However, it is not the author's intention at this time to present herein an all-inclusive analysis of the individual elements, as hydrodynamic forces or soil resistance to lateral motion of the pipeline. It is not a purpose of this paper to investigate effects of functional loads during operation (loads due to weight, pressure, thermal expansion and contraction, prestressing, pipeline geometry in as-laid-conditions) on the steel stresses. Common Design Concept Background. Traditionally it is considered that a pipeline on the seabed exposed to wave and current forces has sufficient stability, if the following expression is satisfied for any instant of the design life