The Stress Analysis of Tubular Joints for Offshore Structures

Abstract

This paper was prepared for the Second European Meeting of the Society of Petroleum Engineers of AIME, to be held in London, England, April 2–3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Operations in rougher areas and the consequent enhanced fatigue problems in the tubular connections led to the development of a finite-element computer program for the determination of stresses in a program for the determination of stresses in a joint. Concurrently a large-scale model test investigation has been undertaken to obtain detailed information on the local stresses close to Use intersection welds. The model tests confirmed the results of tie computer program. Introduction The move of oil exploration to rough o ore areas, such as the North Sea, has confronted the designers of fixed and floating structures with an enhanced fatigue problem. Owing to the high alternating loads resulting from the waves, the structures are subjected to greater fatigue loads, in particular at the intersections of the tubulars, which in general are the highest loaded parts of the structure. Structural analysis programs, together with give environmental conditions, provide a good overall picture and the stress distribution in a structure and picture and the stress distribution in a structure and its components. However, they do not give information on the local effects at the joints. In order to predict fatigue strength it is important to have a reliable method for determining the stress concentrations at the joints. The stress analysis of a joint is certainly not a simple problem and becomes even more complicated for semi-submersibles with large diameter/wall-thickness ratios for the tubulars and reinforcement of the joint by internal and external stiffeners. Reinforcements are present in the latest designs of fixed platforms as well. Results of both analytical and experimental research in this field are known in literature. With one exceptional, they deal with unstiffened K- and T-joints of small diameter tubulars for templatetype fixed structures. Part of KSEPL's offshore research has been aimed at the determination of stress distribution in joints in both fixed and floating platforms. Both a finite-element and an experimental approach have been followed. Starting from plate and shell theory, a finite element program has been developed that is particularly suited to joint research. Special particularly suited to joint research. Special attention has been given to the use of specific elements and to the methods of solving large sets of linear equations without incurring long computer times. The method is able to give detailed numerical answers in the elastic range with a good accuracy and enables us to predict the stress-concentration factors in the joint under consideration.