Presentation on theme: "Edit this text for your title Edit this text for your sub-title Presenter name, location, date etc. MEK 4450 Marine Operations Kværner ASA / DNV, Fall."— Presentation transcript:
Edit this text for your title Edit this text for your sub-title Presenter name, location, date etc. MEK 4450 Marine Operations Kværner ASA / DNV, Fall 2012
Installation of flexibles and cables Typical products Rigid pipes Flexible pipes Cables and umbilicals Installation and installation analyses Installation of end terminations Regular laying Special challenges: shallow water, deep water, slopes, turns etc Waiting on weather
Rigid pipe Large diameter Heavy High laying tension High bending radius Large deck space Expensive equipment Some plastic deformation acceptable Straightening before over-boarding Avoid repeated plastic bending Thermal insulation (wax formation) Concrete weight layers (gas pipes) Courtesy: Bredero Shaw
Flexible pipes Low elastic bending radius Less expensive laying vessels / equipment More competition Separate layers for Axial load Outer pressure Inner pressure Courtesy: NKT Flexibles
Cables Power cables and umbilicals Smaller bending radius, lower unit weight Less expensive vessels / equipment High density Heavy load on a fully loaded vessel Structural capacity and vessel stability Limited plastic bending Courtesy: Nexans
Theory slide. Installation aids Flexible products are installed with various types of vessels with equipment for storage and controlled over-boarding of the products. Typically, the installation of rigid steel pipes requires bigger and more expensive vessels due to the large space and high tension capacity required during deck handling and installation. In the following slides some typical examples are given. The first example shows a laying vessels for electrical cables, where the cables are stored in a horizontal carousel. A horizontal tensioner is used that carries the weight of the cable during laying. The chute over the side of the vessel provides support and prevents damage to the cable as it is over-boarded. We notice that the vessel is equipped with a big crane and a large open deck space. This means that the vessel may be used for other types of marine operations such as installation of subsea modules. Separate slides display the installation equipment used by this vessel. We notice the belt with the orange pads forming the tensioner. The pads are pushed toward the cable to ensure sufficient friction. By running the belt the cable may be pulled in or out. The other slide shows the chute. The next slide shows an alternative configuration, where the cable is routed via a vertical laying tower during installation. The tensioners are vertically mounted in the laying tower. The third slide shows a vessel for installation of small diameter rigid pipe (typically < 12 or 16). Steel pipes are spooled (and deformed plastically) on the large vertical drum in the center of the vessel and installed over a lay ramp. The ramp may be tilted, typically to support a pipe lay angle of degrees. A tensioner that supports pipe lay tension is positioned on the lay ramp, while the reel ensures back-tension. The lay ramp also includes a straightener and a welding/x-ray station. The next two slides show installation vessels with stingers, typically used for installation of large diameter rigid pipes (> 16 or 20). Pipe sections (typically 12 m long) are continuously welded to the pipe string during laying. The large stinger at the stern of the vessel ensures that the pipe is not plastically deformed as straightening is not possible. The last slide displays a typical J-lay vessel for installation of large diameter rigid pipe in deep water. Pipe segments are lifted into the vertical J-lay tower by use of specialized cranes, and then welded to the pipe string during laying.
Typical installation vessels Installation vessel with horizontal tensioner and chute Installation vessel with lay tower Pipe lay vessel with reel and lay ramp Pipe lay vessel with stinger DP vessel Anchor vessel Pipe lay vessel with J-lay tower
Installation vessel with horizontal tensioner and chute Aker Connector
Tensioner / Caterpillar Used to pay in / out product, and to maintain/ support cable tension Belts with pads press against the product Sufficient force to Pull in and overcome friction over chute Support maximum cable tension (e.g. storm) High tension + low radial load capacity => long tensioner / many pads Internal friction in the cable may be lower than friction between cable and pads!
Chute Cable installation Provides continuous support Introduces vessel heading restrictions At maximum design tension Chute structural capacity Product integrity (bending + tension) Over-bending at tip of chute (top angle from analyses)
Installation vessel with lay tower Scandi Neptune Pertinacia Seven Seas
Pipe lay vessel with reel and lay ramp
Pipe lay vessel with stinger
Stinger Provides support for pipes Rollers to reduce friction (=> point loads) Stinger radius above elastic bending radius of pipe Departure angle high enough to prevent over-bending Avoid lift-up of pipe in stinger Will impact vessel motion characteristics NOTE: picture shows stinger in elevated, not operational mode
Pipe lay vessel with J-lay tower Pipe sections raised into vertical Vertical welding of pipe sections Pipe tension supported by clamps
Installation analyses Establish weather criteria and a plan for laying (laying tables) Ensure robust and safe operations for personnel, equipment and flexible product Low tension: over bending, axial compression, loop formation High tension: rupture, tensioner capacity, free spans Ensure that all tolerances are accounted for Determine and verify survival conditions
Installation analyses Shore landing Pull-in to shore Shallow lay
Installation analyses Uphill vs downhill lay Downhill lay More flexible catenary (reduced risk of cable over- bending/compression) May cause high seabed tension and free spans Uphill lay Less flexible catenary (due to geometry) => reduced weather criteria Risk of cable sliding downhill
Installation analyses Laying in steep slopes Difficulty in assessing where actual touchdown point is => step-by-step analyses as input to operational procedures
Installation analyses General considerations (analyses) Deep water High top tension, tensioner capacity Combined tension and bending at vessel interface Curve lay Sliding of product Low lay tension (risk of over-bending/compression) Possible solution: Laying around preinstalled piles etc
Installation analyses Installation of buoyancy elements Step-by step analyses to Determine vessel movements vs. pay-out of pipe/cable Establish procedure for attachment/lowering of clump weight Main challenges Over-bending/compression at vessel interface due to buoyancy
Installation analyses Pull-in to platform Step-by step analyses to Determine lowering of pipe/cable from vessel vs pull-in to platform Main challenges Vessel positioning (available space) Seabed clearance Over-bending at I-tube inlet
Survival condition Cutting of product More critical for power cables and umbilicals Installation of buoyancy elements Establish flexible S- shaped configuration Step by step analysis to ensure product capacity while over boarding buoyancy Analysis gives guidance in when to pay in / pay out after installation Analyses: can the vessel maintain heading and position?