Theoretical and Practical Considerations of Helical Cable Elements Subject to End Effects at Cable Bending

Most cable elements of subsea cables and umbilicals are helical. If helical cable elements are restrained from sliding freely when the cable is bent, large axial strains and stresses will arise in the elements. This paper focuses on the case where the helical cable elements are fixed to end terminations, or to the beneath cable layer, at two points along the cable’s length. The elements can slide freely between these two points. Mathematical expressions are derived to calculate the strains that arise in the helical cable elements when bending the cable segment. The mathematical results have intuitive, practical interpretations that are thoroughly explained. It is shown that the maximum strains and stresses arise when the length of the cable segment is an integer number of pitch lengths plus one half pitch length.