Liebherr Bearings in SMST Telescopic Access Bridges

Since the second quarter of 2014, large diameter bearings by Liebherr have been used in the telescopic access bridges from Dutch company SMST. In this critical application the large diameter bearings have to meet the highest technical requirements, and the company chose Liebherr bearings due to their ideal weight-performance ratio and the company’s engineering expertise. 

How are offshore platforms for oil and gas production or offshore wind power plants provided with supplies? How do employees, that are responsible for production and maintenance, get safely to the facilities? And, how can they leave the platforms quickly in case of emergencies? SMST offers new answers to these questions. 

Their newly developed range of telescopic access bridges allows the safe and comfortable transfer from the support or transportation vessel to the offshore platform – even under rough conditions. The access bridges can be put together individually, and are usually installed on the support vessels.  

As they can swivel around for 360° and are also telescopic, space requirements are minimal. An intelligent control system, together with a powerful hydraulic system, offers an active or passive heave compensation. This ensures the reliable use of the bridge even in heavy seas.  The maximum outreach of the bridges is 58 m, while the maximum load that can be transported over is 1,000 tons. 

Requirements for the main component large diameter bearing

Main components of the bridges, that are very similar to cranes, are the large diameter bearings that allow for the slewing movement. For an ideal design of the luffing gear that compensates for wave movements, the slewing system is positioned relatively low in the tower. The adjustment of the slewing system needs to be extremely precise and fast and compensates for movements of the support vessel directly via a control system. 

For the large diameter bearing, the same requirements as for the bridge itself apply – it needs to operate reliably and safely even under adverse environmental conditions, for example strong side winds. In addition, the effort required for maintenance and service needs to be kept to a minimum and the expected lifetime must be 20 years - the same as the one of the bridge itself. 

The product program of the SMST telescopic access bridges is modular with four main sizes –S, M, L and XL. Within these main sizes there are up to five different jib lengths possible. For a high degree of standardization, SMST was looking for a solution that included the same bearing for every main size – independent of the jib or bridge length.
 
Application and engineering expertise were crucial

SMST placed value not only on quality and performance when it selected the supplier for the large diameter bearings, but also considered the experiences in the offshore sector. “The access bridges will be used in the Gulf of Mexico in 40°C as well as in Arctic regions in -30°C. Therefore, we prefer to work with partners who know exactly what that means for the equipment and the components from their own experience”, Frederik Maats, sales manager at SMST explains. “In worst case scenarios, our bridges are the only way off of the platform.  This means that every single component has to meet highest standards.”  

Liebherr was not the only supplier that was requested to make an offer for the large diameter bearings, but finally won the contract, as the company proved that ball bearing slewing rings are suited for the application – providing a markedly more economic and space-saving solution than the roller bearing slewing rings that were considered at first.  The specified large diameter bearings with interior gear distinguish themselves by a very favorable weight-to-performance ratio. 

The bearing used for the XL bridge size has an outer diameter of 3,400 mm. For low-maintenance, the raceways are automatically lubricated with grease by means of special holes that connect to a central lubrication system. Besides the required calculations for the certifications of the classification bodies DNV GL and ABS, Liebherr carried out additional simulations with FEA to prove the safety of the bearings for the different load configurations with absolute certainty. 

“We liked the open and solution-oriented communication with Liebherr a lot. The close contact and the intensive technical discussions finally lead to the very best solution for our application. Therefore, I can easily picture further collaboration with Liebherr in the future”, Joop Tertstra, purchasing manager of SMST, says about the collaboration with Liebherr’s sales and engineering departments.