Significant size and weight reductions offered by the SPO Compact Flange over conventional flange connections have led to its selection for the Bohai Bay Peng Lai phase two project, for one of the critical elements of the FPSO; the swivel stack.

SPO Compact Flanges from Vector International in sizes from 4 to 16 inches and pressure classes to 1500 are to be used on the swivel stack for the FPSO’s soft yoke mooring, being fabricated by Shenzhen Chiwan Sembawang Engineering, to operate at pressures to over 50 bar, and temperatures over 80°C – well within the capabilities of the flange, which can accommodate pressures to 2,758 bar and temperatures to over 700°C.

The space and weight savings offered by SPO Compact Flanges over conventional ANSI flanges are substantial; typically 70-80% lighter.  A 16 inch Class 1500 SPO Compact Flange weighs some 173kg as opposed to a hefty 570kg for the equivalent rated ANSI flange – a 70% weight saving, and an indication of the significantly smaller size of the compact flange.  Such savings are particularly critical to FPSOs, where space is extremely restricted, and weight needs to be kept to a minimum.

Given the critical role of the swivel stacks, at the heart of the soft yoke mooring system, reliability is equally vital.  The SPO Compact Flange features an internal sealring and triple seal design to provide zero-leak performance.  The flange face geometry (featuring a slight convex bevel with the highest point, the heel, adjacent to the bore and a small outer wedge around the outer diameter of the flange face) creates a wedging action as the flange is closed, until full face-to-face contact is achieved.  The metal-to-metal seal created at the inner diameter or heel is a fully qualified axial seal, while the compressed sealring (located in a groove in the flange face) provides a second, radial, seal.  A small wedge around the outer diameter creates a third, environmental seal.  The result is a reliable, leak-free joint.

“The use of SPO Compact Flanges on this FPSO is indicative of a growing trend, driven primarily by the sizeable space and weight savings and leak-free performance the connections offer,” Vector International vice president marketing and sales Ian Robinson comments.