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									Stressed Skin Living Quarters (LQ) Design




              Petro-Offshore Engineering
                   October 18, 2006
                                                                Content

1   GENERAL................................................................................................................................................... 1
2   STRUCTURAL COMPONENTS.............................................................................................................. 2
3   DESIGN HIGHLIGHTS ............................................................................................................................ 3
4   FABRICATIONS SEQUENCE ................................................................................................................. 4
5   CONCLUSIONS ......................................................................................................................................... 7




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             Petro-Offshore Engineering                  Stress Skin LQ Design


1 General
Most of the offshore oil and gas fields require living quarters (LQ). There are several
types used in the industries: Conventional Trussed Structures, Light Weight Panel,
Crimped Plate Structure and Stressed Skin Structure. The conventional truss
structure is widely used due to easy to design. Light weigh structure has the least
weight, but the long term performance and the safety of the composite materials are
still a concern for large applications. The crimped plate structure is formed by
mechanical force and has large residue stresses and small cracks. Its lateral
strength is also small due to the deformation. Its fatigue life is very difficult to assess,
therefore, this they are mainly used as appurtenances, rather than primary structures,
such as ballast walls.

As more and more deepwater fields are developed, the requirements for lighter
weight structures and higher fatigue performance are increasing. The stressed skin
structure is best suited for the deepwater applications. It will not only increase the
global strength and fatigue life of the structure, but also reduce weight significantly.

The weight reduction for the stressed skin LQ is achieved by using the plates (deck
plates and wall plates) as primary structural members to participate the global
strength analysis. The weight reduction can be as much as 15 to 25% of the
structural weight.

If it is built by shipyards, the stressed skin structure is easy to build compared to the
trussed structures. It can be built by limited crane capacity. The majority of its
welding can be skip type fillet weld, which has less requirements for skilled welders
and NDT.

This type structures also has advantage of penetrations. LQ has significant amount
of penetrations such as architectural penetrations (doors and windows), HVAC
penetrations, piping penetrations and electrical penetrations. It increases the
utilization ratio of the area.

See illustrations of the LQ:




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            Petro-Offshore Engineering             Stress Skin LQ Design


2 Structural Components
The major components are: longitudinal bulkheads, transverse bulkheads, decks, etc.




Bulkhead is made of reinforced plates:




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            Petro-Offshore Engineering                Stress Skin LQ Design


3 Design Highlights
The design is in accordance to major industry specifications. The entire structure is
modeled using ANSYS finite element (FE) program. The yield strength is to meet
API RP 2A and AISC specifications. The buckling strength is to meet DnV 30.1.

The buckling design is completed by stiffened panel design:




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              Petro-Offshore Engineering                   Stress Skin LQ Design



4 Fabrications Sequence
Plates can be pre-fabricated in the shops, then assembled in the general assembling
area:

         Step 1 Place Perimeter L Girders                        Step 1a




               Step 2 Install Level 1               Step 3 Install T. Bulkhead S16500




                                                 T. BH




          Step 4 Install T. Bulkhead S9000           Step 5 Install T. Bulkhead N9000




                                                 T. BH
      T. BH                                      N9000




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            Petro-Offshore Engineering                           Stress Skin LQ Design


    Step 6 Install T. Bulkhead N16500                  Step 7 Install L. Bulkhead W0 (PC 1)


                                                                                        L. B W0




   T. BH
  N16500




     Step 8 Install L. Bulkhead W0 (PC 2)                Step 9 Install Level 2, South Piece


                                        L. BH
                                         W0




                                                    L2 South




    Step 10 Install Level 2, North Piece                 Step 11 Install Level 2, Mid. Piece




L2 North                                             L2 Middle




   Step 12 Install Level 3, South Piece                 Step 13 Install Level 3, North Piece




                                                    L3 South
 L3 North




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            Petro-Offshore Engineering                      Stress Skin LQ Design


     Step 14 Install Level 3, Mid. Piece            Step 15 Install Level 4, South Piece




L3 Middle                                       L4 South




    Step 16 Install Level 4, North Piece             Step 17 Install Level 4, Mid. Piece




L4 North                                        L4 Middle




Step 18 Install L. Bulkhead W11500 (PC 1)       Step 19 Install L. Bulkhead W11500 (PC 2)




 L. BH
W11500                                            L. BH
                                                 W11500




             Step 20 Install Roof                    Helideck Assembly Completed




 Roof




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            Petro-Offshore Engineering                Stress Skin LQ Design


                Helideck Lifted                 Corners at Helideck Connections




                                                                             Connections
                                                                               before




             Install Helideck                           Install Helideck




5 Conclusions
The stressed skin LQ is the best solution for deepwater development. Weight
reduction on the topside will further reduce the weight of supporting structures and
mooring systems. Specially for FPSO, the stressed skin structure is similar to the
hull structure, therefore minimal supporting structure is needed for the LQ module.




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