As the offshore industry is operating in deeper waters, subsea cables and umbilicals are exposed to harsher environments with increasing physical impact and lower temperatures. In the subsea cable and umbilical industry, this calls for an increasing demand of optimal cable designs, requiring accurate analysis models that are verified through physical testing. To improve design tools and cross section analysis tools for optimal cable design, it is important to obtain real mechanical cross sectional measurement data on a wide range of subsea cables' and subsea umbilicals'. It is therefore important that the accuracy of the test methods, including instrumentation for cross section measurement data, is evaluated. A key parameter in cross section analysis is bending stiffness. This paper presents a new method to measure the curvature during a sinusoidal bending stiffness test, on subsea cables and umbilicals, with use of a new sensor based on Fibre Bragg Grating (FBG) technology. To evaluate the accuracy of the new measurement method, a super duplex steel tube with known bending stiffness is used as a reference test sample. Results of the bending stiffness, based on measured curvature performed on the reference test sample, will be presented and compared to the theoretical bending stiffness of the same test sample.


Subsea cables and umbilicals are installed in areas with harsher environments, with increasing physical impacts, and with lower temperatures. This calls for an increasing demand of optimal cable designs, requiring increased analysis accuracy followed by verification through physical testing.

The cable's bending stiffness and the cable elements' bending stresses are among the most important parameters established through cable analyses. The bending sti ness is essential for subsequent analyses as it determines how the cables behave during handling, installation, and operation. The bending stresses relate the cable's bending curvature to the corresponding element stresses which are decisive for analysing the cable's fatigue properties and capacity (allowed combinations of axial cable tension and cable bending curvature).

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