Alternative lifting solutions

Special from Sparrows Group

The lightweight aluminium frame assembled on the boom
The lightweight aluminium frame assembled on the boom (photo: Sparrows Group)

Cranes are an essential piece of equipment utilised on a variety of offshore assets around the globe. These safety critical systems provide a link between the sea and installation, lifting equipment to support onboard operations as well as uploading essential food and water supplies.

Disruption to crane operations can heavily impact activity on the platform, so a robust maintenance plan is crucial. Scheduled checks are regularly carried out by specialist teams to assess and ensure the equipment’s safety and performance. This process also highlights any specific component changeouts which may be required at different stages of the crane’s lifecycle.

As part of a long-term maintenance contract, Sparrows Group, a global provider of specialist equipment and integrated engineering services, was recently tasked with conducting a critical boom and main hoist winch changeout for a major global operator in the North Sea.

Large offshore assets often accommodate more than one crane onboard which can assist with any major component changeouts. However, this particular installation only featured a single pedestal lattice boom crane which added a number of challenges, so a unique lifting solution was required.

Devising a bespoke lifting plan
In line with the planned maintenance schedule for the North Sea operator, it was determined that the main and boom hoist winches on a platform crane required changeout. This was required to mitigate the risk of failure as the length in service had exceeded the component design life. Major component replacements are often necessary to ensure that the systems continue to perform to an optimal level and also adhere to strict safety regulations.

The frame assembled in the Sparrows’ workshop
The frame assembled in the Sparrows’ workshop (photo: Sparrows Group)

The crane winches were mounted in the boom structure which created further challenges. The components would have to be lifted and cross hauled before being lowered through another section of the boom structure to a suitable working area beneath the crane.

Due to platform production and water supply requirements, it was vital for the crane to be returned to service every 7 days, so a time efficient method was crucial.

The devised lifting plan had to assure the weight of both a 2-tonne main hoist winch and 1.5-tonne boom hoist winch could be accommodated. However, it also had to be light enough to make sure the technicians on site could lift the frame, as there were no lifting points above this. After considering various lifting frame designs and scaffolding, an aluminium frame was selected due to its lightweight properties and strength which were suited to the workscope.

Tackling complex structures
The company’s global design team, based in Aberdeen, started work to create the lifting frame with the priority being to keep the design as lightweight as possible. It also had to be easily erected and dismantled once offshore. Building the frame would only take one shift to complete, compared to a four-shift building time for traditional scaffolding. This ensured crane downtime was kept to an absolute minimum.

Frame on the boom – light enough to make sure the technicians on site could lift the frame into place
Frame on the boom – light enough to make sure the technicians on site could lift the frame into place (photo: Sparrows Group)

The parts were built to specification and the frame was assembled and tested at Sparrows’ onshore workshop in Aberdeen. A frame was first manufactured to replicate a crane boom so the lifting frame could be trialled multiple times to assure no issues would arise once transported to the offshore installation.

Once manufactured, the unique lifting frame was deployed to the North Sea asset and eight of Sparrows offshore crew, working in two shifts, executed the winch changeout in several stages. The heaviest part of the final frame was only 23 kg, providing a lightweight but effective solution.

The lifting frame was first secured onto the top chords of the boom structure with the main hoist winch initially replaced. This enabled the crane to return to service to carry out essential lifts only, assuring operations onboard were not impacted.

The frame was then re-assembled to complete the boom hoist winch changeout. Once all components were replaced, the crane was then load tested. This involved suspending various loads in stages up to a 41-tonne proof load using water weights. Following final testing, the crane was returned to service. The full workscope was successfully completed within the timescale and without incident.

Alternative solutions for unique challenges
Maintenance and inspection of safety critical equipment such as cranes is vital to ensure the systems continue to perform optimally over their lifetime. However, it is not a “one size fits all” approach, with offshore platforms often complex structures which require bespoke solutions to address their requirements. Inventive thinking and experienced engineering teams are crucial to creating new and innovative solutions for operators. This ensures the vital ongoing safety and efficiency of the assets and the equipment onboard.

The Sparrows Group is a global provider of specialist equipment and integrated engineering services to the energy and industrial markets. The firm supports customers by delivering a broad range of expert solutions that optimise efficiency and ensure the performance, reliability and safety of critical equipment and people.