Development of High-Pressure Seal and Bearing of Reliable Multipath Swivel

1. ABSTRACT This paper describes the development of a reliable seal and bearing system for a High Pressure Multipath Riser Swivel which can separately transfer different fluids such as produced oil, gas, injection water, etc. Analysis and selection of candidates for the seal and bearing, new innovations and the results of the verification tests are presented herein in detail. 2. INTRODUCTION As a key component of the Floating Production Storage and Off1oading system (FPSO) for exploiting marginal offshore oil fields, A new High Pressure Multipath Riser Swivel was developed from 1985 to 1988, jointly by Japan National Oil Corporation (JNOC) and Mitsubishi Heavy Industries, Ltd. (MHI). This research aimed at developing a compact, light and piggable swivel which could accommodate 8 paths of crude, gas or water. The maximum pressure was 5000 psi and the maximum temperature was 250°F which was deemed satisfactory for most oil fields. (Fig. 1) The structure of the component parts of the bearing and seal, as shown in Fig. 2, have various features which provide performance advantages. A cartridge type seal unit was developed for this swivel for easy fabrication and excellent reliability and maintainability. A new solid lubricant, embedded type, tapered plain bearing was adopted because of its satisfactory friction performance. And, by virtue of the concentricity produced by the bearing shape and the appropriate clearance between the rotating part and the fixed part of the swivel, performance under conditions of thermal expansion and fluid pressure was remarkably improved. 3. DEVELOPMENT OF THE BEARING SYSTEM 3.1 Specified conditions The bearing must maintain thrust load (Wt) and the radial load (Wr), which works on the rotating cylinder, through good friction performance. The swing rotating cylinder is not brought in direct, contact with the stationary cylinder. Clearance(S) between the stationary cylinder and the rotating cylinder must not be changed in order to maintain the sealing performance. 3.2 Selection of shape and material Application of a slide bearing featuring simple construction and limited installation space was studied. The tapered slide bearing shown in Figure 3 was developed after many studies as the correct shape for the large size bearing. The large diameter, heavy weight rotating cylinder can be set easily in the stationary cylinder, fixing the bearing during assembly. The shape of the bearing allows the rotating cylinder to operate evenly on the circumference by preventing clearance variation even if the .beating wears during operation. Thus, high operational stability is ensured. The rotating cylinder is always set on the tapered surface of the slide bearing and has the advantage of being able to self align with the stationary cylinder. 40 to 45° was selected as the tapered angle 8 because the friction coefficient is low and stabilized supporting action can be achieved.