The installation of the 92m of Flare Tower onto FPSO, as shown in Figure 7.7 was studied during detailed design stage of Flare Tower. In general, two methods were discussed as below:
Method A: To install the Flare Tower in two pieces, ie, to cut flare tower at mid section.
Method B: To install the Flare Tower in one complete piece. Advantages:
Method A:
- The Flare Tower weight can be reduced
- No any technical issue during lifting/installation Method B:
- Time saving for both heavy lifting crane and fabrication Disadvantages:
Method A:
- Required two separate lifts
- As the lifting height limitation of Hercules II JibII, the fly Jib is required for installation the upper part. This would lead into time/money costing for the boom changing.
- Safety issue. To connect the upper part onto the lower part, the welding must be carried out up the height of 62m above the sea level. This must be avoided to reduce any potential risk.
Method B:
112 - Required lot of detailed engineering study to ensure safety, clashing
free and cost saving
Method A was not chosen due to high risk up in the air.
For method B, following critical issues were studied carefully:
a) The flare Tower was fabricated on ground. Both main hook and Jib hook were utilized to upbend as shown in Figure 7.6. Additional padeye was designed. Updending structural analysis was performed with the modification of upper leg.
b) After releasing the main hook, the flare tower was lifted by Jib hook only. Hercules then carried the flare for about 2.2 km from fabrication site to integration site. Dynamic analysis was done to ensure the completed system is safe.
c) Prior to installation, the dimension of stab-in guide and Flare leg was checked. Special guide system was designed to receive the tower.
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7.7 Summary
Design and operation for lifting FPSO modules are discussed in this chapter. Lift procedures and considerations for FPSO modules are indicated and rigging systems with multiple spreader bars are highlighted. Practical design and analysis considerations for lifting lower turret, gas recompression module and flare tower, which are unique for stingy requirement of installation accuracy, heavy load and geometry, are discussed based on real projects.
114 Table 7.1 Lifting Operation Summary for Laminaria FPSO
LIFT NO.
AREA
CODE AREA DESCRIPTION WEIGHING SPREADER BAR LENGTH (M)
(Eye to Eye) M O B LIFT WT (TON) 1ST Final BOTTOM 2 NOS TOP 1 NOS NOS OF SLINGS REQ’D
1 HU10 TURRET ( LOWER ) 1ST 680 - - - - 3
2 PF00 FLARE TOWER 1ST 228 Yes Yes - - 2
3 PX20 LAYDOWN AREA FWD TURRET 1ST 46 Yes Yes - - 4 4 PX19 FLARE EQUIPMENT SUPPORT 1ST 70 Yes Yes - 14.080 6 5 PR05 PROCESS PIPERACK 5 1ST 71 Yes Yes - 2.92 6 6 PR03 PROCESS PIPERACK 3 1ST 26 Yes Yes - 4.72 6 7 PR04 PROCESS PIPERACK 4 1ST 25 Yes Yes - 4.72 6 8 PR01 PROCESS PIPERACK 1 1ST 76 Yes Yes - 2.92 6 9 PX18 CHEMICAL INJECTION 1ST 154 Yes Yes 11.565 16.720 10 10 PX01 LAYDOWN AND STORAGE AREA 1ST
212 Yes Yes - 15.840 6 11 PX02 UTILITY AREA 1ST 345 Yes Yes - 18.480 6
12 PX04 POWER GENERATION 1ST 1,120 Yes Yes 13.545 18.480 10
13 PX03 POWER GENERATION 1ST 589 Yes Yes 13.545 18.480 10
14 PM05/ ACCESS / TRANSPORT ROUTE 1ST 45 Yes Yes - 4.72 6
15 HD20 PEDESTAL CRANE X-1402 1ST 92 - - - - 4
16 HD70 PEDESTAL CRANE X-1401 2ND 92 - - - - 4
17 TX00 TURRET – MANIFOLD STRUCTURE 2ND 697 Yes Yes - 4.100 6
18 TX00 TURRET – GANTRY STRUCTURE 2ND 372 Yes Yes - - 4
19 TX00 TURRET – SWIVEL STACK 2ND 50 - - - - 4 20 PX12 PRODUCED WATER 2ND 411 Yes Yes 13.545 18.480 10 21 PX14 CORALLINA SEPARATION 2ND 780 Yes Yes 19.775 18.480 10 22 PX16 LAMINARIA SEPARATION 2ND 700 Yes Yes 19.775 18.480 10 23 PX17 DEBUTANIZER 2ND 307 Yes Yes 11.565 16.720 10 24 PX09 GAS RECOMPRESSION 3RD 875 Yes Yes 19.775 18.480 10
25 PX11 GAS LIFT 3RD
906 Yes Yes 19.775 18.480 10 26 PX13 GAS LIFT 3RD 967 Yes Yes 19.775 18.480 10
27 PX15 GAS INJECTION 3RD 1,066 Yes Yes 19.775 18.480 10
28 HU90 DEBUTANIZER COLUMN 3RD 95 - - - - 4
Table 7.2 Contingency Actions Plan / Procedure
SCENARIO PRIMARY
CONTINGENCY
SECONDARY CONTINGENCY Breaking/parting of either
shear leg or FPSO mooring line
Standby mooring rope Tug's assist Failure of shear leg to
lower load Lower boom Maintain crew to repair Power failure on shear leg
crane
start emergency
generator automatically
None Bad weather The lifting operation
115 Table 7.3 Preparation Check List
DESCRIPTION WOS LOC SME
Asian Hercules vessel in position at Erection yard, ready for lifting operation.
Slings, shackles and spreader bar are ready Certificate for sling, shackle and cranes LOC to have checked the lifting gears Certificate for Spreader bars
Qualified rigging supervisor and safety officer are present Shiploosed items removed from module and list prepared Bearing Pads and connecting bolts are ready
Erection area cleared of temporary equipment and obstructions.
Temporary access way to the lifting trunnions Movable crane standby
Table 7.4 Loadout Check List
DESCRIPTION WOS LOC SME
Hercules II is proper anchored and moored in its lifting position
Check mooring line conditions
Shackle and slings are in good condition and attached on module
loadout area is clear of any obstruction This procedure reviewed by all the parties
Agreement to commence lifting operations. Certificate of Approval for Lift issued by LOC.
Table 7.5 Installation Check List
DESCRIPTION WOS LOC SME
Hercules II mooring its designed position with two mooring lines tie on FPSO, two aft anchors dropped Set-down area on FPSO is clear of obstacles, ready to receive it.
Footing level/location survey done, trimmed if necessary Bearing Pads and connecting bolts are ready on FPSO Hull deck
LOC certificate provided to commence lifting Agreement to lower down module
Module leveled and proper installed
Minimum bolt connection approved by LOC Agreement to release crane hook
116 θ2 θ1 CG θ4 θ3
Fig. 7.1 Rigging arrangement for lifting FPSO modules with spreader bars
One spreader bar
Two spreader bars
3 spreader Bars θ2 θ1 CG θ3 θ θ2 θ θ3 θ1 CG
117 Figure 7.2 Lifting of Lower Turret (680 ton)
Figure 7.3 Lifting of Upper Turret – Manifold Deck Structure with Three Spreader Bars
118
• As the Gantry Structure is transported to installation yard on Barge “Sea
Prosper”, proper seafastening removal procedure was established prior to lifting;
• The four slings are also very carefully selected due to COG eccentricity
Figure 7.4 Lifting of Upper Turret – Gantry Structure
Single sling is attached to Swivel Stack with the balanced system to crane hook. Figure 7.5 Lifting of Swivel Stack – Bottom Assembly
119 Figure 7.6 Lifting of Gas Recompression Module
120 Figure 7.7 Upending and Lifting of 92-metre Flare Tower
121
CHAPTER 8 SPECIAL LIFTING FRAME DESIGN
8.1 Introduction
A versatile lifting frame is designed for the loadout / installation of six pallets (topside structures) onto Shell EA FPSO at Sembawang Yard.
The weight and COG of six pallets used for the lifting frame design is listed in Table 8.1. As we can see from Table 10.1, the COG for each pallet is different from other. Also, the lifting point distances in Y-direction for Separation Pallet port and Power Generation port are not the same as others. It is a challenge to make an uni-frame used for 6 lifts.
The final design weight is based on the pallet self-weight with 15% contingency plus lifting frame weight and rigging weight. Dynamic factor of 1.5 is considered at the same time. The design is performed in accordance with API RP2A and AISC (American Institute Steel Construction) Allowable Stress Design 9th Edition. The lifting frame analysis is performed by the software SACS (Structural Analysis Computer System).
With the lifting frame weight and rigging weight, the total weight used in analysis is listed in table 8.2.
The hook point is 26 meters high from the lifting frame for all pallets except the pallet Power Generation Port, in which the hook point is 16 meters considered due to hook height limitation. Tube check and joint/overlapping check against API RP 2A are made and the dynamic factor of 1.50 is considered. It is found that all members and joints are sufficient. The maximum stress ratio for member check is 0.86 on the member 2-4 when pallet Power Generation Port is lifted in Table 8.3.
122
8.2. Effect of the Shift of the Centre of Gravity