Connecting multi-bore structures in water
A method for connecting sections of a multi-bore structure in water comprises connecting the sections to bring corresponding bores of the sections into mutual alignment while those bores are each closed by a plug that excludes the water from the bores. Then, with the sections connected and the corresponding bores sealed together in fluid communication with each other, the plugs are flushed away in a flushing fluid that flows along the communicating bores.
1. A method for connecting sections of a multi-bore structure in seawater, the method comprising:
connecting the sections to bring corresponding bores of the sections into mutual alignment while those bores are closed by respective plugs that exclude seawater from the bores;
initially shielding the respective plugs from seawater with watertight caps before connecting the sections;
subsequently exposing the plugs to seawater by removing the watertight caps from the bores to expose the plugs to seawater before connecting the sections; and
with the sections connected and the corresponding bores sealed together in fluid communication with each other, flushing away the plugs in a flushing fluid that flows along the communicating bores;
wherein flushing away the plugs in the flushing fluid comprises dissolving and/or fragmenting the plugs in the flushing fluid.
2. The method of claim 1 , comprising connecting the sections when the bores are substantially submerged in seawater.
3. The method of claim 1 , comprising allowing gas to escape from at least one of the bores around a plug situated in that bore.
4. The method of claim 3 , comprising deforming said plug under fluid pressure of the gas.
5. The method of claim 1 , wherein the flushing fluid contains water.
6. The method of claim 5 , wherein the flushing fluid is substantially fresh water.
7. The method of claim 1 , wherein the flushing fluid contains a glycol.
8. The method of claim 1 , comprising exposing at least one of the plugs to a differential fluid pressure of at least two bars before connecting the sections.
9. The method of claim 1 , preceded by force-fitting the plugs into the bores with an interference fit.
10. The method of claim 1 , preceded by bonding the plugs into the bores.
11. The method of claim 1 , comprising exposing the plugs to seawater for at least one hour before connecting the sections, while keeping the bores closed by the plugs.
12. The method of claim 1 , comprising equalising the pressure on opposing sides of the respective watertight caps prior to removing the watertight caps.