VOGA Offshore Basket Design – DNV 2.7-1

The Challenge:

VOGA required a new basket design for the transport of 4 x chemical Bulki Bin tanks offshore.

The Solution:

Cube Offshore were engaged to develop a basket design in accordance with the requirements of DNV 2.7-1

The design encompassed the following attributes:

• Secure offshore transport
• Chemical containment in the event of tank rupture
• Ease of tank rigging access for personnel
• Avoidance of tank rigging snag points.

The Scope:

The scope of work included:

• Concept development
• Detailed design in accordance with DNV 2.7-1
• Detailed drawings for fabrication
• Fabrication specifications in accordance with DNV 2.7-1
• Certificate of Compliance for Lifted Equipment (CCLE)

Structural member code check / compliance                              Plated sides FEA – Von Mises Stress Plot

Lift configuration / rigging schematic

The Challenge:

The underdeck drain access platform on VOGA’s WNB platform was severely corroded and required replacing.

The Solution:

Cube Offshore were engaged to develop a modular replacement concept and carry out detailed structural design of the replacement access platform.

The design encompassed the following attributes:

• modular design to minimise handling and offshore construction
• component design to fit through existing under deck scaffold
• full structural design compliance with the revised VOGA WNB Basis of Design

The Scope:

The scope of work included:

• Basis of Design
• Functional Specification
• Concept development
• Detailed engineering design in accordance with ISO 19901-3 including:
  • Operating (5yr non-cyclonic) – ULS-A
  • Extreme (100yr cyclonic) – ULS-B
  • Accidental (2000yr) – ALS
  • Extreme Seismic – ELE
  • Abnormal Seismic – ALS
  • Component lift design to DNV 2.7-3 R30 rating
• 3D modelling, fabrication drawings & dxf files
• Modular construction for transport & offshore lifting
• Fabrication specifications.

Early modular concept                                                             Staad.Pro analysis model

Staad.Pro analysis output                                                          3D CAD model – exploded view

Component lift analysis (DNV 2.7-3 R30)                             Component lift design (DNV 2.7-3 R30)

The Challenge:

Cube designed, manufactured, tested, coated & delivered a DNV 2.7-3 R30 SXX MGW=8000kg rated subsea basket to client specifications in 6 weeks over the over the Christmas / NY break.

The Solution:

In order to manage the tight schedule, Cube locked down all client specifications early, committed to early steel procurement in parallel with the design process then issued fabrication drawings, cutting lists & .dxf files directly to our fabricator.  Close communication and scheduling over the Christmas / NY break allowed all workfronts to progress in accordance with the plan.

The Scope:

Deliver a subsea basket in accordance with the strength, fabrication & testing requirements of DNV 2.7-3 R30 SXX MGW=8000kg as follows:

• Concept development
• Comply with client specifications & functional requirements
• Engineering design in accordance with the strength requirements of DNV 2.7-3 R30 SXX
• Manufacture & test in accordance with the material & testing requirements of DNV 2.7-3 R30 SXX
• Integrate design & manufacture processes
• Expedite a quick turn around for load testing & coating

The Challenge:

CCI own a Hydraulic Workover Unit (HWU) which they deploy offshore onto production platforms for cost effective down-hole intervention.  Upcoming onshore contracts required an Onshore Support Base to be designed & fabricated to support the HWU on land over the well head.

The Solution:

Cube Offshore were engaged to develop the concept and carry out detailed structural design of the Substructure.

The arrangement comprised the following components:

• 4no. corner Support Pods to transfer loads into the ground
• 2no. Spreader beams to span between the Support Pods and provide support for the loads above
• 1no. Sub-Base Module sitting atop the Spreader Beams:
  • Supporting the 191t jacking loads
  • Supporting a 35t BOP
  • Support the HWU tower above c/w all dead, personnel & functional loading
• All components were configured to be road transportable throughout WA without the need for a pilot
• All components were liftable in accordance with DNV 2.7-3 R00 requirements
• Ease of assembly with minimal use of bolting, instead adopting clamped, bearing and turnbuckle connections
• Design compliance with API Spe. 4F – Drilling & Well Servicing Structures

The Scope:

The following was delivered as part of an integrated project approach & full collaboration between design engineering, fabrication and client:

• Basis of Design & Functional Specification
• Concept development
• Detailed engineering design & 3D modelling
• Fabrication drawings, dxf files and NC files
• Fabrication support
• Assembly procedures

1. Staad.Pro structural analysis                                                                  2. Staad.Pro 3D model

3. AutoCad 3D model exported to Navisworks                4. Completed structure assembled for operation

5. BOP suspended under Sub-Base Module

The Challenge:

Subsea conductor spacers on the Jadestone Stag platform had been dislodged by wave loads resulting in a long unsupported conductor span with cyclone season imminent.

The Solution:

he conductor guide in question was surrounded by adjacent conductors which prevented ROV access and prohibited diving.  Cube therefore developed a remotely installable conductor spacer system for installation from above using rope access.  The spacers were developed in 4no. quadrant shapes that could “self-install” when lowered from above.  A release line was then pulled to deploy to 2no. wedges per quadrant to lock the spacer into position.  The spacers were specifically designed such that they could not be dislodged by high vertical hydrodynamic forces, as the original design had.   Engineering checks confirmed the strength & stability of the spacers and the local conductor wall for structural integrity

The Scope:

• Concept development
• Detailed engineering design & modelling
• Manufacture
• Full scale SIT / Function test
• Engineering & manufacture documentation

3D modelling of the spacers confirmed fit & functionality prior to manufacture.

Installation sequence confirming fit & functionality.

In order to further verify the design, a mock-up of the conductor and guide was built and a successful System Integration Test carried out for installation, deployment & operation of the spacer system.

Challenge:

Seadraulics (formerly Specialist Offshore Services) required structural, piping & geotechnical engineering design support to deliver the structural “module” component of their SHFM design.  The SHFM subsea structure had demanding specifications such as deployment to seabed at (-)4000m, electrical/hydraulic ROV interfaces, 2 x chemical dosing bladders, flooding system & filters, loading arm and pressure testing facilities.

Cube Scope:

• Structural design in accordance with DNV 2.7-3 / AISC 360-10
• Piping design to ASME B31.3
• Geotechnical design to API RP 2A / DNV-RP-C205
• 3D interchange of CAD files between mechanical and structural models and Inventor / Solidworks for full clash check

Outcome:

Critical file management of the 3D Mechanical models in Inventor and Structural models in Solidworks for weekly integration and clash checking allowed for a seamless design process.  Structural design incorporated Chinese steel sections for COOEC fabrication.  No clash problems with fabrication as a result of integrated approach to combined 3D module models.

Offshore risers were discovered with missing subsea support clamp bolts as part of a routine subsea survey.

Cube were engaged to deliver an engineering solution leading to a permanent repair, including:

• Incident review & assessment dating back to original fabrication & installation
• Develop a diver installed remedial solution c/w installation methodology
• Procurement, manufacture & delivery of clamp repair components

Cube were selected to develop an innovating strengthening design to improve the structural integrity of an existing topsides module on the Woodside NGujima Yin FPSO.

The following design characteristics were achieved:

• Phase 1 strengthening work was all bolted and carried out during normal operations
• Phase 2 strengthening work (deck remedial scope) was welded and scheduled for future shipyard implementation
• Full integration with the offshore construction team to develop a sympathetic design for access, handling and installation operations
• All analysis carried out using Bentley SACS
• Limit state ULS / ALS (ISO19902) combined with ship motions, environmental loading and deck deflections.
• CAD models integrated with Point Cloud survey data for clash checking
• Significant reduction in module primary steel and deck utilisations achieved

Photo comparison with Point Cloud image.

SACS analysis showing original high structural utilisations prior to remedial bracing.  Deck not modelled.

SACS analysis showing topsides with remedial bracing & reduced utilisations.  Preliminary deck steel modelled showing high utilisations

SACS analysis showing extended deck model and longitudinal bracing to redirect and reduce deck utilisations.

Phase 1 – bolted bracing / strengthening to improve topsides integrity – implemented on station during normal operations

Phase 2 – welded longitudinal bracing to improve deck integrity – implemented in the shipyard during scheduled maintenance visit

Cube were engaged by Woodside to provide independent Review & 3rd Party Verification services for their NRA Caisson Removal Project.

Challenges included corroded caisson sections with limited survey detail inside guide locations with a risk of dropped object during removal.  Engineering adopted a risk-based approach with mitigations designed into the removal methodology.

Woodside’s gas compression trains up in Karratha are key to their continuous delivery of NWS gas to customers.  In order to keep it that way, critical spare rotor shafts must be available and is a preserved condition for whenever needed.  To ensure that this happens, Cube Offshore developed, manufactured & tested a range of 5no. dedicated Rotor Cocoon Skids designed for the following criteria:

• Rotors secured inside cocoons using adjustable restraints
• Pressurised containment of Nitrogen gas inside cocoons to preserve rotors
• Horizontal lifting, upending and vertical lifting (Woodside & DNV 2.7-3 specifications) c/w rotor under pressure
• Road transport & forklift handling

5no. Rotor Cocoon Skids in vertical storage position:     

Vertical lift of Rotor Cocoon Skid due to careful lift point placement:

Rotors secured inside cocoons for all loading scenarios:   

Progress photo during manufacture:   

Rotor Cocoon Skids – 3D CAD model representation:

Vertical lift analysis extract showing plate stress and member utilisations:

Challenge:

As part of the INPEX Ichthys phase 2 drilling campaign, the Casing Setback Area needed to be raised by 1.5m.  Design loading was 436t, no offshore hotwork allowed,  the platform was to be easily removable and overhead lift access on the rig was restricted.

Scope:

• Interface with INPEX and Maersk Drilling stakeholders to resolve BoD & concept
• Concept development & detailed design for operating & installation load cases
• Manufacture & testing of 3no. casing Setback “pods”
• Design, manufacture & testing in accordance with DNV 2.7-3
• Certificates of Conformity for Lifted Equipment

Outcome:

After early liaisons with INPEX & Maersk Drilling personnel, a comprehensive Basis of Design was agreed and a 3-part “pod” concept developed to aid both functionality & installation limitations.  The individual “pods” were safely lifted into position then connected together to form a single Casing Setback Platform.  No hotwork was required for the installation of the platform and lifting analysis for a vertical lift and side lift provided for lifting options.  Cube further proposed that all timbers be pre-installed & secured which greatly reduced offshore installation risk & effort.

Offshore Lift

Client feedback:

Great work all and thanks to Andrew, Emily and Steve especially for coordinating.  That was a great late in the day call to pre-install the wooden blocks.

Malcolm Reid

INPEX Drilling Superintendent

Challenge:

As part of the Woodside Ngujima-Yin FPSO modification & upgrade for the Greater Enfield project, three highly critical riser valve stacks (2.5m and up to 6t) needed to be transported offshore, lowered into the turret area and installed onto the buoy.  The turret area was highly congested with vertical and side access.

Scope:

• Detailed 3D modelling of the entire turret area with installation lift paths clash checked
• Design, manufacture & testing of a 6.5t WLL lifting davit to be mounted onto the buoy swivel pedestal.
• Design, manufacture & testing of 3 x dedicated valve stack lifting frames (DNV 2.7-3)
• Detailed Lift Plans for the installation of all valve stacks & equipment (x 7)

Outcome:

By importing a range of different software model files to create a single model, Cube Offshore produced a highly detailed & accurate digital 3D space of the FPSO turret area.  3D models of the valve stack installation paths were developed to establish the lift plan and generate a detailed 3D clash check.  This significantly reduced risk for the offshore installation operation.

Subsequently, Cube Offshore applied their design, manufacturing and lifting knowledge to deliver fully certified mechanical handling equipment and detailed Lift Plans.  At all stages, Cube actively communicated and integrated with the Woodside team to incorporate existing knowledge and lessons learned.

Client feedback:

Hi Gents,

I was going to send a note back to our contracting office letting them know how good a job Cube has done on the Greater Enfield scopes. ..

Thanks,

Scott Cranston
Completions Lead
Offshore Commissioning & Start-up Team (OCST) 

Greater Enfield Project
Woodside Energy Ltd.