On the Development of Rules for Building and Classing Spar Based Systems
Authors: Grove Todd , Forsyth J. David , Montaruli Bret , Tan Pao-Lin , Breuer J. Andrew 
Published: October 2008

As industry continues to gain practical experience in the use of spar related technology for offshore floating production applications, there is a need for relevant engineering standards. The availability of specific, appropriate, authoritative and consistent acceptance criteria is required to ensure the safety of the people aboard, the spar system, and the surrounding environment. This paper follows the evolution of classification requirements for spar based systems. This covers determination of the relevant acceptance criteria for early examples of the technology through collection of the requisite body of practical experience to permit formulation of comprehensive, collated classification standards, or Rules. Availability of such criteria follows the industry's tradition of ensuring consistency in the design, fabrication, installation and subsequent operational maintenance of offshore structures to an acceptable level of safety. This paper includes a summary of the approach to the development of criteria focusing on hull and deck structures, marine and safety systems, production facilities, stability, mooring, and the requisite surveys during fabrication, installation and operational life.

Introduction

The active utilization of spar related technology in recent years has been yet another example of innovation in the offshore industry. Associated with such innovation is the need to accurately assess these designs with respect to ensuring an acceptable level of safety for the people working on board, the unit, as well as the environment. Classification has traditionally fulfilled this need and continues to enhance its capabilities in response to emerging technologies. The foundation of class is the standards, or Rules, by which such systems are assessed. In the case of spars, the American Bureau of Shipping (ABS) has not published explicit classification rules. In such cases a three-tier approach is followed to cover the scope of approval work to enable classification. Where appropriate components of other related existing rules are available these are applied to the unit. Alternatively, in some instances relevant industry standards are available, which can be drawn upon. Examples of the applicable standards in these first categories are referenced herein. Finally, in those cases where there are no readily available applicable standards, class and the designer will work in cooperation to reach an agreeable acceptance criteria. In this situation, class will be looking to establish that all criteria ensure an equivalent level of safety as related to other similar applications. This allows suitable flexibility to permit classification of new technologies while still ensuring proper oversight and attention to safety issues.

Following the compilation of a body of practical experience with an innovative technology, class will look towards consolidating the various standards into a set of Rules specific to the application. For the present case, ABS has developed this body of knowledge with spar based systems and hybrids, including classification and/or certification work, on the projects summarized in Table 1 along with other developing projects.

ABS is proceeding towards publication of a guide, or "preliminary" rules for spar based systems based on the approach that has been developed and applied in conjunction with these projects. This paper summarizes this approach for the major system components and thus provides a "blue print" that will be utilized in the production of the Spar Guide.