Three load cases are to be considered:
Installation case
Operating case (riser column connected) Operating case (riser column disconnected)
Additionally, two environmental scenarios are to be considered for the operating load cases:
1. Cyclonic, including surface wave and associated steady current effects (riser column disconnected)
2. Non-cyclonic, ignoring effect of surface waves and associated currents with cases as shown below:
100 year steady current (from tide and drift - riser column disconnected) 100 year soliton current (riser column connected)
Note that installation conditions are considered to be the 1 year RP wave and current.
7.17.2 Design Method
The flowlines will be analysed for on-bottom stability in accordance with the following:
The methodology to be used for analysis of the cyclonic environmental scenario (item 1 as per section 7.17.1) is DnV RP E305 (reference /S4/) Simplified Method using Technip in-house software Stabil (reference /A10/).
The methodology to be used for analysis of the non-cyclonic environmental scenario (item 2 as per section 7.17.1) is the force balance method in accordance with reference /S5/.
3D stability analysis is to be performed for any flowlines found to be unstable using the force balance methodology described above. This methodology will be submitted for approval prior to use (reference /A13/).
Linear (Airy) wave theory shall be used with the simplified method in accordance with DnV RP E305 (reference /S4/). As no waves are applicable to the force balance methodology, no wave theory is required for this.
7.17.3 Design Parameters
The hydrodynamic coefficients used will be in accordance with DnV RP E305 (reference /S4/) sections 5.3.8 and 5.3.12, with due consideration of the Reynolds Number and other dimensionless parameters. This is applicable for both the simplified and force balance methodologies.
For all flowlines except the production and production/test the flowline contents shall be product at minimum density for the 100yr non-cyclonic (including soliton) conditions, and the 100yr cyclonic conditions (operation cases as per section 7.17.1).
For the production and production/test flowlines the flowline contents shall be as follows:
Product at minimum density for the riser column connected case.
When the riser column is disconnected the production and production / test flowlines will be depressurised and the contents will quickly settle out, leaving the density of the inner fluid the same as the gas lift minimum density as given in note a) of section 7.10.3.
The flowline contents shall be empty for the 1yr non-cyclonic conditions and 1yr internal wave conditions (installation case as per section 7.17.1).
Environmental data shall be as per section 5.14, with the directionality of the current accounted for by applying the component of the current perpendicular to the pipe axis.
No marine growth is to be included for on bottom stability analysis (reference /B2/).
For cyclonic conditions (item 1 as per section 7.17.1) to be carried out using the simplified method as per DnV RP E305 (reference /S4/), a lateral friction coefficient of 0.7 will be used (reference /B2/).
For non-cyclonic conditions (item 2 as per section 7.17.2) to be carried out using the force balance methodology, a lateral friction coefficient as per section 5.15 will be used (reference /B2/).
Seabed roughness is as per section 5.15.
No self embedment is to be considered.
See design data sheet for on bottom stability included in Appendix K.
7.17.4 Acceptance Criteria
The minimum submerged weight of the pipe must exceed the maximum required weight for stability calculated using DnV RP E305 (reference /S4/) simplified method or force balance method. Note that DnV RP E305 (reference /S4/) allows lateral pipeline displacements of up to 20m under certain circumstances.
Alternatively, if 3D dynamic stability is carried out then the following is to apply (reference /B2/):
Flowline lateral displacement due to environmental loading is prohibited in the locations where the flowlines cross the exposed escarpment feature.
Flowline lateral displacement in other locations (including drill centres and riser / flowline interface) will be considered acceptable pending acceptable loadings and curvatures.
Lateral displacement onto MODU anchor exclusion zones is not acceptable.
APPENDIX A Drawings FPSO East Subsea Facilities Layout
Drawing No: SK1580, Rev C
FPSO Flexible Flowline & EHU Approach General Arrangement Drawing No: K2000DX002.0001, Rev 3
Anchoring Anchorlegs General Arrangement Drawing No: K 4060 D S 001 0001, Rev C
Riser Column Riser Column General Arrangement Drawing No: K 4101 D G 001 0001, Rev C
Riser Column “J” Tubes Layout
Drawing No: K 4101 D S 007 0001, Rev D RTM Mooring System General Arrangement
Drawing No: K 4101 D S 010 0001, Rev A Top of Column General Arrangement
Drawing No: SB 81327 DCM97024, Rev C1 Riser Column Compartmental Arrangement Drawing No: SB 81327 DCM97022, Rev C1 Riser Column Central Shaft Structural Details
Drawing No: K 4101 D S 003 0001, Rev 1
E-DC1 Flexible Flowline & EHU Approach (Rigid Xmas Tree Tie-in Spools) General Arrangement
Drawing No: K2000DX003.0001, Rev 2
E-DC2 Flexible Flowline & EHU Approach (Rigid Xmas Tree Tie-in Spools) General Arrangement
Drawing No: K2000DX004.0001, Rev 2
E-DC3 Flexible Flowline & EHU Approach (Rigid Xmas Tree Tie-in Spools) General Arrangement
Drawing No: K2000DX006.0001, Rev 2
E-DC4 Flexible Flowline & EHU Approach (Rigid Xmas Tree Tie-in Spools) General Arrangement
Drawing No: K2000DX007.0001, Rev 2 Anchoring Anchorlegs Details Sheet 1
Drawing No: K 4060 D S 002 0001, Rev A Anchoring Anchorlegs Details Sheet 2
Drawing No: K 4060 D S 002 0002, Rev 0 Anchoring Anchorlegs Details Sheet 3
Drawing No: K 4060 D S 002 0003, Rev 0
APPENDIX B FPSO RAOs Data
APPENDIX C Fatigue Wave Data
APPENDIX D
Dynamic Analysis Load Case Matrix
APPENDIX E
Description of Dynamic Analysis Load Cases Titles Signification
The description of the dynamic analysis load cases titles signification is as follows:
XX_YYY_www_O Where:
1. XX is the load case number as per the load case matrix included in Appendix D.
2. YYY is the riser being considered:
Pd9 for the 9” production risers Pd8 for the 8” production / test riser Gi6 for the 6” gas injection riser Gl6 for the 6” gas lift riser
Wi10 for the 10” water injection riser 3. www is the analysis type:
nom for nominal load case sen1 for sensitivity study 1
sen2 for sensitivity study 2 etc with the sensitivity numbered as per section 7.10.5.
4. O is an unused parameter at this stage.
APPENDIX F
Pressure Conversion Calculations
APPENDIX G
Gas Injection Back Flow Fluid Composition
APPENDIX H Sand Erosion Data
APPENDIX I
Location of Forces on Manifold / PLEM Hubs
APPENDIX J
Additional Chemical Injection Details
APPENDIX K
Design Data Sheet for On Bottom Stability
APPENDIX L
Extreme Riser Connected Motion Details
APPENDIX M
Riser Fatigue Analysis Methodology
APPENDIX N
Production Flowrate Details
APPENDIX O
Riser Column Motions During Disconnection
APPENDIX P
Referenced Correspondence
APPENDIX Q Topside Piping Loads
APPENDIX R Slugging Data