THREE-POINT FLANGED SKID FOR TURBOMACHINERY OFF-SHORE INSTALLATION
Stefano BARTOLOZZI, Turbocompressors and Steam Turbine Division, Nuovo Pignone, Florence ITALY
Giovanni CIANFERONI, Turbocompressors and Steam Turbine Division, Nuovo Pignone, Florence ITALY
Stefano GENEROSI, Technical Scientific Calculation Dept., Nuovo Pignone, Florence ITALY
INTRODUCTION
One of the most important aspects to be considered in offshore installation of turbomachinery is the interface between the machine skid and the main structure.
The whole structural design must be such that under the most severe static and dynamic loads machine alignment is maintained to acceptable levels whether the rotating machinery is installed in a module or directly on the platform deck. Two structural solutions achieve the above conditions; the multipoint skid, typically used the main structural stiffness permitting, and the three point skid that is used whenever the main structure displacements are too high for conventional baseplates.
Three-point skids are being used increasingly because they can withstand displacement of their supporting deck without being affected by additional stresses or misalignment.
Some of the disadvantages of this solution are as follows:
- non-standard gas turbine baseplate as it must accommodate the driven machinery also
- non-standard centrifugal compressor baseplate as it should accommodate the driver skid also
- weight increase,
- increased delivery time.
In order to minimize such disadvantages a coupled skid arrangement, based on flanged connections and suitable for large three-point skid applications, was developed. With this solution the gas turbine and the centrifugal compressor baseplates can be manufactured, assembled, tested and shipped separately, and then easily assembled on site.
These flanged connections need a special design. They must restore the original structural behavior of the integral beams. They must allow an easy installation procedure adopting adequate construction tolerances and systems capable of recovering any tolerance exceedances.
With such a design, the two skids can be manufactured in different places and even b y different companies.
Since the aim of the connection design is to restore the continuity of the beam, the following hypotheses were formulated:
- considering a load condition consistent with the worst expected combination of weight and arrangement
- maintaining positive pressure on the whole mating surface
- considering the shear stress borne by a special pin.
This configuration was checked by finite-element analysis which allows detailed sizing of all of the structural components as well as the bolts that must ensure contact under the established conditions by their preload.
This article describes a coupled skid arrangement, its geometrical characteristics and the relevant finite-element method of verification, as well as two projects in which it has been successfully applied.
