Advanced hydraulics for testing of flexible risers

You can read the full article from Maskinmesteren in Danish about the new test bench for NOV (Flexibles) for testing flexible oil risers here or read the extract below. Serman & Tipsmark has supplied the hydraulic solutions for the test bench.

 

Facts about the test bench for NOV Flexibles

  • The test bench simulates 20 years' physical stress on flexible risers at sea

  • The test accelerates 20 years' stress to 9-12 months

  • The test bench can test risers measuring 17-22 metres in length and up to 16 inches in diameter

  • The test bench can simulate the pulling of flexible risers of up to 2.5 km in length

  • The test bench can pull at 600 tons / 6 mega Newtons (MN)

  • Internal pressure during the test up to 700 bar

  • Internal temperatures up to 135°C

  • The test bench itself weighs 115 tons

  • The test bench is designed to be able to deliver 76 million strokes – a stroke is a single movement to and fro with a cylinder

  • Serman & Tipsmark has developed and produced the hydraulics system, as well as the control system

  • R&D A/S has been consulting engineers

 

 

The risers are pulled out to deeper water

On the new test bench for Flexibles, a so-called full scale test is conducted in a 17-22 metre section of a completed flexible rise which consists of several risers placed layer-upon-layer over one another. Typically, the test involves five different types of riser to ensure strength and flexibility. The risers can be several kilometres long and they have to spend many years in a harsh environment at sea...

 

Requirement for energy-optimised test bench

One of the requirements stipulated by Flexibles has been for an extremely energy-optimised test bench. Serman & Tipsmark have fulfilled this wish with a flexible pump solution whereby five pumps of different sizes can be connected and disconnected as required. Each pump has an individual electronic control system which helps to ensure a high degree of efficiency.

"Besides the requirement for energy efficiency, the solution had to be extremely flexible in terms of performance and very precisely controlled right down to a tenth of a millimeter," explains Kristian Eis, Technical Manager of Serman & Tipsmark.

He highlights one of the technical challenges faced: To compensate for the friction that is normally generated in hydraulic cylinders.

"Cylinder friction can be a challenge in terms of the precision in stress loads and thus the data measurements. Moreover, friction is not energy-optimal. Therefore, we have produced a solution with special, powerful guides. However, we can't use position sensors because they are not able to withstand physical impacts of this size. Instead, we use special pressure transmitters. We have also used FPGA controls to ensure a rapid response time. PLC is too slow a technology for this purpose," he continues.

The test bench has four cylinders that can be used for different types of physical force on the flexible risers. At each end of the flexible riser there are so-called End Fittings, which close the risers and enable internal pressure to be applied to a riser – in addition to controlling the temperature, so that it is possible to simulate the changing conditions when oil and gas is transported through the risers from the bottom of the ocean up to the vessel on the surface of the ocean.

 

State of the Art components

According to Serman & Tipsmark there are very few suppliers who would be able to supply such a solution:

"We are very good at extreme and special requirements. I believe that the suppliers who would have been able to supply the solution we have produced for Flexibles are in the minority. We are talking about an advanced solution in which mechanics, electronics, computer programming and controls all have to interact so that you get not only a solution that is highly energy-optimised, but also a solution in which it must be possible to control the hydraulics, and thus the physical stress, in an extremely precise manner, " says Nørgaard Nielsen.

"We also had an American supplier bid for the project but they failed to understand that energy consumption is an important parameter for us. They wanted to supply something akin to a V8 engine so that there was enough power. But we simply do not need such large pump capacity. We need an intelligent, flexible, energy-optimal solution with extremely precise hydraulic controls," says Søren Gaarde, Test Engineer at NOV Flexibles.ristian Eis points out that the solution for Flexibles is an advanced mechatronic solution – i.e. a hybrid solution of mechanics and electronics. "We have supplied the physical components, controls, programming and the controls used are the same ones that are used to control robots. All components are State of the Art. A crucial part of the design has been to avoid delays in the hydraulic controls. Consequently, the components have been placed as close as possible to the processes in which they are involved," he says.