Bundles and towed installation

Bundles and towed installation

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All possible different cases are analysed, with different combinations of flowlines running hot or remaining at the ambient seabed temperature. The outer carrier is fully constrained by the cold seawater, so the bundle does not expand and contract like a normal pipeline on the seabed near the spoolpiece. That means spools do not have to accommodate a lot of bending moment. Near the tow and trail heads the last 50 m (160 ft) or so of the carrier wall is generally thicker – at around 20 mm (¾ in) – than the rest of the bundle. This is to accommodate the stresses during tow-out and beach handling. The intersection between the wall and the bulkhead may also be radiussed. In order to accommodate the flaring, radii and resulting stresses, it may be necessary to rearrange the spatial arrangement of the flowlines for the end section of the bundle.

SPACERS

SPACERS

ƒ Maintain optimum stability configuration ƒ Flowline clamped support prevents bending and buckling ƒ No welding to lines ƒ Rollers attached to assist in bundle assembly

ƒ Typical centres 10 m to 15 m (30 ft to 45 ft) ƒ Partial intermediates for smaller diameter lines ƒ Tray for umbilical tubing

Subsea 7 Leadon field bundle

The flowlines are held in position by spacers. These are bolted on in separate stages during the assembly process, as the flowlines are brought together from their linear alignment (side- by-side) in the welding stations to the relationship they adopt within the bundle. Some of the spacer units have rollers to enable them to slide along the bottom of the carrier pipe, which is assembled separately. Small diameter lines may require support and fixity against buckling at more frequent spacing than shown above. These intermediate spacers may be bolted to a larger pipe. Control tubing elements may need a continuous tray, since the support normally provided by the umbilical armour layer is not present.

BPKINNOULL BUNDLE LAYOUT