Motor Removal Offshore Angola

Background

An 18-ton gas lift compressor motor, located on COB-P1 platform offshore, was scheduled to be removed and transported onshore for refurbishment / overhaul.  The motor was located on the 2nd level of the gas compression module – known as “Module A” – which was a steel framed structure located on the deck of the main platform.

Although the COB-P1 platform was equipped with cranes on both the West and East sides, each with a Safe Working Load capacity of 20 tons, these cranes were unable to perform the motor lift due to their insufficient lifting capacity at the required radius.

Given the high cost and limited availability of suitable barge cranes, our client NPE reached out to us to help design a more affordable and effective alternative.  Thunder Cranes  conducted site surveys and studies in the process of designing the proposed solution.

Challenges & Solutions

Key Challenges:

• Challenging Rig Up Location
• Space Constraints
• Gas Environment
• Heavy Lift – 18MT

Solutions:

• Multiple site surveys and studies were required before the methodology could be confirmed. Many aspects of the job – from rig up procedure, to equipment and materials – needed to be customised, or fabricated, specifically for this project.
• To carry out the critical lift, Thunder Cranes proposed the TC20 portable-modular stiffleg crane. We determined that the TC20 could be rigged up and positioned above the motor – on the top deck of Module B located adjacent to Module A – and so would then be in a position to lift the 18MT motor in a single lift from the platform to the supply vessel.

Modular Cranes

• TC05 & TC20 stiff leg cranes. Due to the insufficient reach radius of the platform crane, a TC05 crane would need to be employed as a rig-up assist crane for the TC20 and a new TC20 rig up sequence was designed specifically for this job.

Boom Length & Wire Rope

• The ideal TC20 boom length in this scenario was the 40ft boom since it would contain fewer parts, and be faster and easier to assemble in the limited space.
• As the 18MT lift required a 4-part reeve the TC20 winch was therefore re-spooled with 700ft of wire rope to cover the vertical distance of the lift (120ft).

Clamping System

• With no hot work permitted, we deployed our clamping & bolting systems to secure the crane base beams to the module structure.
• Custom built spacers were needed under the TC20 base beam due to obstructions (large pad eyes) which could not be removed and this in turn required the fabrication of longer stud bolts on the clamping system.

Zone 2 Powerpack

• To deal with the gas environment we provided Zone 2 certified diesel powerpacks as the prime movers for our hydraulically operated modular cranes.

Scaffolding

• In addition, with limited handrail and grated deck spaces on the top of Module B, scaffolding with work floors were needed to provide additional / temporary decking at the top of the module.

Rope Access & Specialised Rigging

• The motor was located underneath the top deck of Module A, and would need to be lifted out from the side of the structure, not through the top which was not possible without the removal / dismantling of beams, piping and/or process equipment.
• To bring the motor out though the side of the structure, our partners at NPE designed a customised extension beam and trolley system, which once installed, together with a customised rigging and load transfer system and a rope access technician, would enable a “hand off” of the suspended load from the beam and trolley to the TC20.

Steps/Sequence of Work