Topside Decommissioning - A Case Study
As offshore platforms near the end of their life, their fixed cranes may no longer be operational or may lack sufficient lifting capacity for topside module removal in the decom stage. Modular rental cranes from Thunder Cranes offer an economical and safe solution for topside preparation works such as "weight shedding" prior to topside removal by the heavy lift vessel.
Case Summary
Chevron Thailand engaged Thunder Cranes to assist with the decommission preparations works.? The requirement was to remove equipment and associated P, E & I? (approx. 300MT) from main deck.? This “weight shedding” was carried out to bring the topside weight to within the heavy lift vessel (HLV) lifting capacity for topside removal.
The “reverse-installation” process consisted of isolating & disconnecting all lines connecting to equipment, and disconnecting equipment skid base from deck plate.? The equipment modules could then be lifted from the main deck to a supply vessel for later disposal or recycling.
Located on the top deck there were 14 large components weighing between 10 to 40 tons, as well as a number smaller components of various weights below 10 tons.? Since the existing platform crane capacity and reach radius was not sufficient for the project, the TC90 modular rental crane was proposed, which has a maximum capacity of approximately 60MT for offboard lifts.
Our client had explored other options for module removal – such as hiring a barge crane. However, Thunder Cranes’ modular rental crane was the best solution from the viewpoint of ensuring safe, static lifting, as well as from the viewpoint of cost and time savings.
Comparison of Options
Option 1 – Preparation by Platform Crane and Heavy Equipment Removal by Heavy Lift Vessel (HLV).
Option 2 – Preparation by Platform Crane with TC-90 & Remaining Heavy Equipment by HLV.
Challenges & Solutions
Challenge #1?– The platform had very limited space for rigging up and no exposed beams on which we could apply our TC90 clamping system. Therefore welding with dog plates was required to tie down modular crane.? This was implemented safely and without any issues within 3 days with one shift of welders for a total rig up time of 6 days including load testing.? In addition, due to limited space on the platform deck, the supply vessel was on standby within reach of the platform crane, allowing the rig up and rig down of the TC90 crane on the fly.
Challenge #2 – Some of the larger modules at the limit of the TC90 reach radius did not have verified weight information.? A decision had to be made on whether to reposition the crane for those lifts or whether to disassemble and breakdown down those modules into smaller components.? Upon further study it was concluded that the best way forwards was to breakdown some of the modules. In addition, we deployed our most experienced lifting superintendent on site to supervise the most critical lifts.
Planning
Our process starts with a thorough assessment of the client’s lifting requirements, platform drawings, general specifications, and project timelines. A site visit is then conducted to verify that an appropriate and practical solution can be proposed.
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Our proposal and quotation come with a Site Visit Report to clearly communicate the proposed method with drawings and photos.
After the proposal is given the green light, we begin the detailed planning stage where we collaborate with the client to customize elements of the project in terms of materials, equipment, 3rd party services, utilities, scaffolding, etc.? Customization can include any platform modifications if needed, or any re-positioning, or removal of elements from the main deck of the platform.
Furthermore, our modular crane configuration is customized to meet specific needs with regards to the tied down method, boom reach radius, zone rating, or any other safety or environmental considerations.
In the next step an engineering work pack is submitted to the client addressing the specific scope of work and lifting requirements, featuring detailed considerations from the site visit, with comprehensive rig up and lifting plans, customized layout and positioning drawings, as well as reaction force calculations needed to conduct a structural analysis.
Pre-mobilization planning includes risk assessment/hazard identification, and alignment sessions are conducted for offshore personnel to ensure safe and efficient operation of the modular cranes.
Depending on the project location, the preparation and deployment of the modular cranes and auxiliary equipment might begin months ahead to ensure cranes are at the load out port and ready to be transported to the offshore site and assembled according to the pre-planned schedule and project configuration.
Timeline
Outcome
The project objectives were successfully met to our client’s satisfaction, within schedule and without incidents or hinderances.
Conclusion
By removing the production modules the overall platform weight was reduced to be within the capacity of the heavy lift vessel which was able to remove the topside and structure in one lift.
Approximate costs savings from the chosen option with TC90 was estimated at $USD 1.5-2.0 million from savings in preparation duration (1 months) & HLV duration (5d).