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Thialf

In the oil and gas sector, fields are increasingly being tapped into in waters that are too deep for platforms with permanent foundations. In these cases, the HMC vessel is deployed for the direct installation of equipment on the seabed, ranging from subsea production facilities through to mooring systems for floating platforms. In the framework of these projects, lifting operations sometimes have to be carried out in water depths in excess of 2,000 metres. Deepwater installation

During subsurface operations, the hook elements – the most crucial components of any crane – come into contact with seawater. At a height of more than six metres, each hook element with its four points rotates around a solid roller bearing, coated in consistent grease. The seals from Trelleborg are required to protect the bearing against seawater, the corrosion it causes, and the wearing action of metal parts on metal. At the same time, the seals make sure that the shaft of the hook is able to rotate smoothly. Any interruption to normal operation can have financial consequences for HMC. Better solution

As explained by Jurgen de Jong, Senior Technical Superintendent for cranes at HMC, “The seals that were used in the past were unsuitable for the job and during underwater applications, the hook elements came into contact with seawater.” One of De Jong’s tasks is the planning of repairs, inspection and certification of the crane blocks. “In 1999, HMC and Trelleborg joined forces to identify a better solution,” said Ralph van de Grijp, Sales Manager at Trelleborg Sealing Solutions Netherlands. “Based on the specifications provided by HMC, we developed a proposal to use a double-action seal. This seal prevents the leakage of fluids in both directions: the seawater cannot penetrate into the bearing, while the lubricant is prevented from leaking into the outside environment.”

Unusual

The solution finally selected by the partners was the Turcon Roto Glyd Ring from Trelleborg, a system already widely used in other sectors. The diameter of 1.8 metres nonetheless made this an unusual application. Over the next ten years, the Thialf undertook a series of lifting operations during which the bearings in the hook elements operated satisfactorily, without any major problems. When the ship returned to its home base in Rotterdam for maintenance, in 2010, the functioning of the seals could be evaluated. Trelleborg Sealing Solutions were approached with the request to inspect and replace the seals, a job that took three days for each seal. The results were astounding. Extraordinary

“Never before had my colleagues seen seals in such good condition after ten years in an extreme working environment,” commented Van de Grijp. “There was only evidence of minimal wear,” added De Jong. “The bearing and the inside of the block were in excellent condition, tangible proof that the seals had done their job.” Nonetheless, HMC still decided to install new seals. “Normally speaking, during the maintenance of a block, all seals are automatically replaced, preventing the need to dismantle the entire system again, should one of the seals start to leak after all,” explained De Jong. The burning question left in the minds of Van der Grijp and his colleagues at Trelleborg Sealing Solutions, however, was: how much longer would the original seals have been able to continue functioning correctly? Turcon Roto Glyd Ring

The Turcon Roto Glyd Ring PTFE seal is activated by an elastomer O-ring. As the liquid pressure from seawater or oil increases, so does the force with which the O-ring pushes the PTFE seal against the opposing surface. This principle maintains the seal in its intended position. 2012

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Offshore Holland 3 | 2012  

Offshore Holland is een hoogwaardig, Engelstalig relatie- en promotiemagazine voor de internationale olie- en gasindustrie. Het doel van het...

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