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ABSTRACT In this paper, the results of finite element analyses of API BX swivel flanges are presented. The interactions between the flange, the gasket, and the bolt preload are studied and illustrated. Two analytical approaches are explained, one with gasket in the model and the other without. The assumptions made in the analysis are scrutinized. Four failure criteria of a flange connection are identified and discussed for the subsea applications. Based on the comparison between the two models, the significance of gasket inclusion on the load carrying capacity is concluded. For the subsea applications, including the gasket in the analysis gives a more conservative yet realistic prediction than the model without gasket. INTRODUCTION Finite element analysis (FEA) has been utilized to determine the load capabilities of flange connections (Refs. 1 & 2). However, most of them were performed without a gasket being included in the FEA model. A Joint Industry Project (JIP) Study 'Swivel Flange Design Practice Development' was sponsored by eight companies and awarded to Cameron Offshore Engineering (COE). The original objective of the study was to determine the load carrying capacity of seventeen swivel flanges so that they may be implemented into the API 17D Specification. As a side-study, the effect of including the gasket in the finite e1ement mathematical model was also investigated. The reason for the side-study was the discovery that the load carrying capacity disclosed by the model with a gasket was lower than the API published data. Four criteria selected to define the load capabilities of the swivel flanges are:the allowable stresses in the flange and hub bodies,the allowable stress in the bolt,the pressure leakage, andthe hub face separation. The first three requirements are general for any pressure containing equipment. For subsea connections, the flange face-to-face contact must he maintained so that no seal fretting will occur due to the cyclic loading, It was also found that the load carrying capacity defined by the hub face separation criteria is the most conservative among four. The finite element model with gasket being included is an elasto-plastic, large displacement, non-linear analysis. There are three load paths through the gasket and the flange face, It was found that the load required to seat the gasket is 40% to 60% of the bolt preload. This significantly reduces the load remaining at the flange contact face. The inclusion of the gasket in the FEA model is the source of the discrepancies between the current study and API PRAC 86-21 (Ref. 3). TECHNICAL APPROACH TO FLANGE ANALYSIS Traditional Flange Analysis Approach vs ABAQUS CAXA Flange connections are axisymmetric in geometry. The makeup load, the pressure load, and the tension are all axisymmetric, only the bending moment is not, In the past, the bending moment was included in the axisysmmetric model by the equivalent tension modeling scheme, that is only valid for one sectional plane.